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Nickel laterite Part 1 ndash microstructure andphase characterisations during reductionroasting and leaching

M A Rhamdhani1 P C Hayes2 and E Jak2

Detailed microstructure and phase characterisations of processed nickel laterite ore feed

reduced ore and leached ore have been carried out using scanning electron microscope

synchrotron X-ray powder diffraction and electron probe X-ray microanalysis as a part of study

aimed to increase Ni recovery from the laterite ores The majority of the nickel in the ore feed were

found to be associated with fine grained goethite (Fe rich matrix of limonite composite) and

serpentine particles These phases were transformed to magnetite and olivine respectively upon

reduction roasting Nanosize metallic particles were also observed on the free surface of limonite

composite particles following reduction roasting Upon leaching 90 of the nickel in the Fe rich

matrix was leached out while 50 was removed from the olivine and its composites The

characterisation results from this study were used to assist the analysis of thermodynamic and

phase changes during reduction roasting and leaching described in Part 2 of the paper

Keywords Nickel laterite Caron process Laterite reduction Laterite leaching Nickel processing

IntroductionNickel metal is extracted mainly from sulphide andoxidehydroxide laterite ores which constitute ofapproximately 36 and 64 of the nickel reserves in thewestern world respectively1 The continued depletion ofhigh grade nickel sulphide ores high cost of fuel strictenvironmental regulations and energy intensive natureof pyrometallurgical processing have led to greaterefforts to improve recovery of nickel from laterite ores2

In general nickel laterite is comprised of two chemicallyand physically distinct ore types ie saprolitic (silicatehydrosilicate) and limonitic (oxidehydroxide) ores Thefour basic processes3 currently used to extract nickel fromthese ores include smelting electric furnace reductionhigh temperature and pressure acid leaching and reduc-tive roastammonia leaching with the Caron4 process Thefirst two processes are usually used to process saproliticore as the nickel has to be liberated from the crystal latticeof the materials The last two processes are commonlyused for extracting nickel from limonitic ore as the nickelwhich is relatively loosely bonded to goethite [FeO(OH)]can be selectively reduced and leached

At the BHP Billiton Yabulu refinery5 nickel andnickel oxide are produced from a mixture of limoniticand saprolitic laterite ores through a modified Caron

process Nickel laterite ores are processed throughreduction roasting in a reducing gas atmosphere inmultiple hearth roasters followed by ammoniacal leach-ing The resulting liquor is refined by solvent extractionand subsequently basic nickel carbonate is precipitatedto form an intermediate product The basic nickelcarbonate is then partially reduced in a rotary kilnbefore final gaseous reduction to nickel metal compacts

A number of studies have been reported on themineralogy and geochemistry of selected laterite oredeposits6ndash11 Chen et al6 in their study conductedmineralogical and electron microprobe (EPMA) char-acterisation of nickel laterites from New Caledonia andIndonesia and Gleeson et al7 analysed nickel lateritesfrom Colombia While this information is useful it doesnot provide detailed information about the microstruc-ture phase changes or nickel distribution before andafter ore processing which are important for theoptimisation of the process metallurgy

In addition a number of studies have been carried outto determine the effect of the process parameters on thenickel recovery412ndash19 Caron4 investigated the effect ofthe physical nature of the ore and its original chemistryparticle size reduction temperature leaching tempera-ture leaching liquor composition and other reductionand leaching practices on the nickel recovery fromlaterites De Graaf1213 studied the effect of differentreduction roasting and leaching conditions on the nickelrecovery from limonitic and saprolitic laterite ores andreported that effective reduction occurs when it iscarried out at partial pressure of H2 or CO of at least15 199 Pa (015 atm) at a temperature range of 550ndash650uC The nickel recovery from the leached ore is

1Faculty of Engineering and Industrial Sciences Swinburne University ofTechnology Hawthorn VIC 3122 Australia previously with Pyrome-tallurgy Research Centre University of Queensland2Pyrometallurgy Research Centre School of Engineering the University ofQueensland Brisbane QLD 4072 Australia

Corresponding author email ARhamdhaniswineduau

2009 Institute of Materials Minerals and Mining and The AusIMMPublished by Maney on behalf of the Institute and The AusIMMReceived 9 December 2007 accepted 16 February 2009DOI 101179174328509X431391

Mineral Processing and ExtractiveMetallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 129

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reported to increase with decreasing particle size inboth types of ore and the addition of sulphur as pyritein the ore is reported to be beneficial to the nickelrecovery De Graaf also suggested that unextractablenickel in saprolitic ore is associated with the formationof recrystallised olivine (Mg2SiO4) or enstatite(MgSiO3) in the reduced ore as had been inferred byHayashi14

Valix and Cheung1516 using synchrotron radiationX-ray powder diffraction technique studied the phasetransformation of precalcined laterite ores during hightemperature reduction in COCO2 gas mixtures at fixedratios In the case of limonite ore they reported that theoptimum Ni recovery was obtained when the orereduction was carried out at 600uC The X-ray diffrac-tion spectra indicated that under reducing conditionsgoethite in the limonite ore was transformed tomagnetite at 400uC The X-ray spectra also indicatedthe formation of iron nickel alloy (taenite) however attemperatures 700uC they observed a significantdecrease in the alloy X-ray peaks In the case ofreduction of precalcined saprolitic ore they observedthe transformation of serpentine to forsterite olivine(2MgOSiO2) at 700uC This however was not observedwhen the reducing gas was introduced before thedehydroxylation of serpentine instead fayalite olivine(2FeOSiO2) was formed The addition of sulphur wasreported to suppress the formation of forsterite duringreduction roasting of the saprolite

None of the studies412ndash19 described above provideinformation on the changes on the microstructure andnickel distribution in the phases at microscopic level as aresult of the reduction and leaching only limitedinformation can be found in literature20ndash22

During the reduction roasting and leaching complexchanges in the materialsrsquo microstructure phase nickeldistribution and other characteristics are occurringUnderstanding these changes is important not onlyfrom the point of view of understanding the underlyingscience but also for improved control of technologicalapplications as they strongly affect the overall nickelrecovery from the ore

The principal aims of the current studies are toprovide detailed quantitative information on micro-structure phase and nickel distribution changes and toevaluate the thermodynamic of the reduction roastingin support of increasing Ni recovery in industrialoperations The approach taken in the current studiesis to

(i) systematically characterise (using various techni-ques) the processed laterites obtained fromindustrial operations

(ii) reconcile these results to provide quantitativedescriptions of the materials

(iii) relate this information with the thermodynamicand phase change analysis of the materials tocharacterise the important reactions taking placeduring the processes and to identify importantoperation parameters influencing Ni recovery

In Part 1 of this series of papers microstructure andphase characterisation results including the Ni distribu-tion on the phases present in the laterite processed in theplant are reported The analyses of the microstructureand thermodynamic of phase changes in the materialsare described in Part 2 of the series

Experimental

MaterialsNickel laterite samples used in the study were suppliedby BHP Billiton Yabulu refinery and were obtainedfrom various locations in the plant5 these include

(i) ore feed ie processed ore feed to multiplehearth roasters

(ii) reduced ore ie ore from the exit of a coolerafter multiple hearth roasters

(iii) leached ore ie residue from the leaching carriedout in laboratory

Process conditionsThe nickel laterite ore used was a mixture of limoniticand saprolitic ores (of approximately 70ndash30 mass-)imported from New Caledonia Indonesia andPhilippines In the process the mixture was fed torotary driers and then to ball mills where they wereground to fine powders The fine ores were then mixedwith fuel oil reductant and reduction roasted in multiplehearth roasters to a maximum temperature of 740uCunder a reducing condition The reducing conditionsachieved in the reactor were a result of partialcombustion of fuel oil and supplementary hydrogenadded to the hearths From thermodynamic calculationsand mass balancing of gas components of the input andoutput streams of the reactor the effective oxygenpartial pressure pO2

inside the reactor was estimated tobe 32610215 Pa (102195 atm) The ores exited themultiple hearth roasters at 680uC and were directlycooled in rotary ore coolers under reducing conditionsbefore quenched into an ammonium carbonate aqueoussolution

In the current study leaching of the reduced ore wascarried out in laboratory The leaching tests were carriedout in cylindrical vessels in 561024 m3 of ammoniacalsolution (consisting of 80 kg m23 NH3 70 kg m23

CO2 and 1 kg m23 Na2EDTA) Ethylene diamine tetraacetic acid (EDTA) was added into the leaching solutionwith the purpose of avoiding the formation of ferrichydroxide precipitate that may affect the concentrationof dissolved metals in the leaching solution To simulateindustrial conditions the leaching tests were carried outin two stages First the slurry was aerobically leached forone hour at ambient temperature and 116761025 m3 s21 air the air was first sparged through561024 m3 of aqua ammonia before introduction tothe leach After aerobic leaching the slurry was vacuumfiltered and subsequently leached anaerobically in261024 m3 of fresh leaching liquor for three days at40uC After anaerobic leaching the slurry was vacuumfiltered and dried at 110uC to obtain the leached oresamples

Analysis techniques and sample preparationElectron probe X-ray microanalyses were carried outusing Superprobe JEOL 8200L (JEOL Ltd TokyoJapan) equipped with five wavelength dispersive detec-tors The EPMA was operated at 15 kV acceleratingvoltage and probe current of 15 nA Standards (MgOquartz SiO2 hematite Fe2O3 chromite FeCr2O4 Al2O3

and NiO from Charles M Taylor Co Stanford CA)were used for the calibration of the EPMA measure-ments In addition to the EPMA analyses scanningelectron microscopy (SEM) observations were carried

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out using Phillips XL-30 (Phillips FEI CompanyHillsboro OR) and cold field emission JEOL 63006400 with accelerating voltages 15 and 20 kV respec-tively Elemental bulk analysis of the samples wascarried out using the inductively coupled plasma atomicemission spectroscopy technique Bulk sulphur andcarbon compositions of the samples were analysed usingLECO CS-444C-S (LECO Corp St Joseph MI)

To enable the examination of mineral sections the oresamples were mounted in epoxy resin and cured in avacuum chamber Cross-sections of the samples werethen prepared by polishing using SiC paper anddiamond paste (down to a 025 mm size) After cleaningthe mounted samples were then sputter coated withcarbon or platinum using Eiko IB-5 Sputter Coater(Eiko Co Ltd Hitachinaka Japan) For SEM surfacemorphology observations the powder samples after theexperiments were directly placed on a carbon tabattached to an aluminium pin stub before being sputtercoated with carbon or platinum

Synchrotron radiation based X-ray powder diffrac-tion (SXRD) analysis was carried out on the BigDiffpowder XRD beamline at the Australian NationalBeamline Facility at the Photon Factory TsukubaJapan Approximately 1024 kg subsample of the oreswere mixed with 10 mass- NIST 640C Si standard thenground using an agate mortar and pestle under ethanolfor 5 min before experiments X-ray wavelengths of08 A and current of 400 mA were used in the analysesThe exposure time was 20 min per sample

The particle size distributions were measured usingMastersizer 2000 (Malvern Instruments LtdWorchestershire UK)

The approach taken in reconciling the data in thecurrent study is as follows

(i) EPMA analysis was used to characterise thecompositions of the phasesparticles The aver-age compositions of the phasesparticles reportedin the current study were calculated from EPMAanalysis of at least 20 points from similar phasesparticles

(ii) the proportions of these phasesparticles inthe ore samples were determined by estimatingthe area percentage of each phaseparticle on theSEM images of the ore samplesrsquo sections using

image analysis software The results were cross-checked through mass balance considering theEPMA measurements and inductively coupledplasma atomic emission spectroscopy bulk com-position analyses

(iii) the distribution of elements in particular Nibetween phases was determined by multiplyingthe estimated phase proportion by the averageconcentration of elements in that particularphaseparticle measured by EPMA

Results and discussion

Bulk composition particle size distribution andsynchrotron XRD resultsThe elemental bulk compositions of the ore feedreduced ore and leached ore samples are given inTable 1 The corresponding compositions of the orefeed reduced ore and leached ore samples recalculatedto oxides and their normalised values given in bracketsare also shown The normalised values were calculatedby dividing the mass- of individual oxide by the totalmass- of metal oxides and multiplying by 100 It canbe seen from Table 1 that the major components in theores are iron silicon and magnesium

The particle size distributions of the ore feed reducedore and leached ore samples are shown in Fig 1 The orefeed consists of particles with size varying from 02 to700 mm with mean particle size of 21 mm About23 vol- of the materials have a size 5 mm and only6 vol- are 100 mm

Table 1 Bulk elemental and their corresponding oxide compositions of dried ore feed reduced ore and leached oresamples (values in bracket are normalised)

ElementsOre feedmass-

Reduced oremass-

Leached oremass- Oxides

Ore feedmass-

Reduced oremass-

Leached oremass-

Al 183 207 216 Al2O3 346 (402) 391 (403) 408 (416)Ca 021 026 026 CaO 029 (034) 036 (037) 036 (037)C 033 123 139 C 033 (038) 123 (127) 139 (142)Cr 155 169 158 Cr2O3 227 (263) 247 (254) 231 (235)Co 014 014 005 CoO 018 (020) 018 (019) 006 (006)Fe 332 350 372 Fe2O3 4746 (5515) 5004 (5152) 5318 (5414)Mg 565 709 680 MgO 937 (1089) 1176 (1211) 1128 (1148)Mn 074 076 068 MnO 096 (111) 098 (101) 088 (089)Ni 161 179 038 NiO 205 (238) 228 (235) 048 (049)K 002 005 005 K2O 002 (003) 006 (006) 006 (006)Si 909 1089 1109 SiO2 1944 (2259) 2329 (2398) 2372 (2415)Na 002 004 004 Na2O 003 (003) 005 (006) 005 (005)S 011 040 025 S 011 040 025Ti 004 004 005 TiO2 006 (007) 007 (008) 008 (008)Zn 002 002 002 ZnO 003 (003) 003 (003) 003 (003)Sum 5456 6148 6200 Sum 8606 (100) 9712 (100) 9823 (100)

1 Particle size distributions of ore feed reduced ore and

leached ore samples

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There was a change in the particle size distribution ofthe ore samples upon reduction roasting as shown inFig 1 The distribution was shifted to the right themean particle size of the sample was increased from 21to 43 mm The volume percentage of particles with asize larger than 100 mm in ore was increased from 6 to13 vol- The changes in the distribution were mainlyassociated with the agglomeration of the materials uponreduction roasting

The mean particle size of the leached ore sample was35 mm smaller than that of reduced ore ie 43 mm Itcan also be seen from Fig 1 that the distribution isslightly shifted to the left The volume percentage ofparticles with a size 100 mm in the leached ore samplesis 57 vol-

Synchrotron X-ray powder diffraction analyses werecarried out on the ore feed reduced ore and leached oresamples to identify the crystalline phases present in thematerials The resultant SXRD spectra are shown inFig 2 It can be seen that in the case of ore feed samplethe major peaks present are identified to be from

goethite [(FeNi)O(OH)] serpentine-lizardite[(MgFeNi)3Si2O5(OH)4 quartz SiO2] and spinel Fe-chromite [(FeMg)O(Cr Al Fe)2O3] The peaksobserved in the reduced ore sample are of olivine[(MgFeNi)2SiO4] magnetite [(FeNi)OFe2O3] quartzspinel Fe chromite and taenite (FeNi) alloy The peaksobserved in the leached ore are similar as in the reducedore however the peaks of taenite do not appearconfirming the nickel dissolution upon leaching

Ore feed sampleTable 2 shows the summary of the average compositionsof the particles and phases observed in the ore feedsamples measured using EPMA The results arepresented in terms of oxides composition (mass-) andare average values of multiple measurements conductedon a number of similar particlesphases The composi-tions presented are normalised values It should be notedthat in the case of goethite (and fine grained matrix) andserpentine the total counts of the EPMA measurementare 100 due to the present of water of crystal-lisation For simplicity only particles with a proportion1 are reported Trace elements observed in eachphases such as Ca Mn Cu Ti Na K Zn Pb and Coare also not reported

The approximate proportions of the various particles(mass-) in the sample as well as the relative propor-tions (on average) of phases present in each observedparticle are also presented in Table 2 (in columns 2 and5 respectively) These compositions were approximatedby reconciling mass balance using the results of EPMAmeasurements SEM observations and chemical bulkanalysis (Table 1)

Figure 3a shows an example of an SEM image(backscattered electron image) of the ore feed sampleat low magnification showing the general microstruc-ture of the particles The greyscale in the image showsthe relative mean atomic number of the material thusrepresenting differences in compositions The numberson the images were assigned to represent a particularparticle type or phase according to Table 2 In generalcomplex structures such as composite intergrowthvein-likeplate-like porous and dense structures wereobserved in the particles in the ore feed sample

2 Synchrotron X-ray powder diffraction spectra (synchro-

tron radiation wavelength 08 A) of nickel laterite ore

feed reduced ore and leached ore samples [L lizardite

(serpentine) G goethite Q quartz Si silicon stan-

dard O olivine M magnetite S spinel (Fendashchromite)

T taenite (FendashNi alloy)]

1 limonite composite particle 3 magnetite 5 chromite 7 serpentine 9 quartz 11 Fe rich matrix 12 goethite 13magnetite 17 serpentine

3 Scanning electron microscope backscattered electron micrographs of ore feed samples showing a overview of micro-

structures of particles and b detailed microstructure of limonite composite particle (no 1 in a)

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In the current discussion the ore particles wereclassified into two categories ie single phase andcomposite particles The single phase particle refers toa particle that consists of only a single phase (with orwithout small amount of inclusions) The compositeparticle in this case refers to agglomerated particles withvarious phases embedded in a matrix or a blend(intergrowth) between two or more phases or mineralgrains

It can be seen from Table 2 that the major phasesmixtures observed in the ore feed sample include Fe richmatrix (a fine grain mixture of goethite and silicateminerals) goethite and serpentine Other phasesobserved include quartz olivine magnetite and chro-mite Trace phases (not included in Table 2) observedinclude CandashMg silicate (diopside) forsterite nickeloan(NiO2MgO4SiO2) FendashMn silicate pyroxene[(MgCaFeNi)SiO3] and gibbsite [Al(OH)3] In thecurrent study general mineral species names werereported no attempts were made to distinguish theprecise mineral species

Limonite composite particles

The majority of the coarse particles 60 mass- of thetotal ore sample were limonite composite particles ieparticles consisting of fine grains of Fe rich mineralmatrix with inclusion phases embedded in it (labelledno 1 in Fig 3a) The limonite composite particles inaverage contain of 70 of Fe rich matrix and 30 ofother phasegrain inclusions Most of these limonitecomposite particles have sizes in the range of hundredsof micrometres The remainder of the coarse particleswere no 7 (serpentine 26 mass-) and other singlephase particles such as no 3 (magnetite) no 5 (chro-mite) and no 9 (quartz) as shown in Fig 3a Magnetiteand chromite phases appear bright in the backscatteredelectron images and others appear as darker grey phases

Figure 3b shows in more detail the limonite compositeparticle This particular composite consists of smallergrainsphases of no 12 (goethite) no 13 (magnetiteappear as bright phases) and no 17 (serpentine)embedded in no 11 (Fe rich matrix) The inclusionphasesgrains in the matrix have different types ofmorphology such as needle-like plate-like and roundshapes with a size ranging from 1 mm to tens ofmicrometres

The matrix of the limonite composite particlesconsists mainly of Fe and other elements such as SiMg and Al in lower concentrations Considering thelarge concentration of the matrix in the ore feedsamples and by reconciling with X-ray powder diffrac-tion analysis results it was concluded that this matrixmainly consists of a mixture of fine grained goethite withsilicate minerals ie serpentine

There were variations in composition in the fine grainmatrix between particles and within a particle Thenickel oxide concentration in the matrix was found tovary from about 005ndash to 620 mass- In the particle inFig 3b the average nickel oxide concentration in thematrix was 214 mass- For comparison the nickeloxide concentration of no 12 (goethite) inside thelimonite composite particles was 142 mass- onaverage It should be noted that no separate NiO orCoO particles were observed The clear indications fromthe analyses are that the Ni and Co are present in dilute

solid solution mostly in the goethite magnetite serpen-tine and olivine crystal lattice

Serpentine particles

Serpentine was present as a single phase (dense orporous) particles as well as composite particlesexamples of these microstructures are shown in Fig 4There were variations in composition between serpen-tine particles (in terms of MgFe ratio and mass-NiO)and within a particle in some of the serpentine iedemonstrated by two or more different grey regionsInclusions (such as magnetite) may also be present insidethese serpentine particles Figure 4a shows a singlephase large serpentine particle with dense morphology(a particle size of 500 mm) A single phase serpentineparticle with two different grey areas is shown in Fig 4bIn this particular particle the light grey area has a lowernickel oxide concentration compared to the darker area162 and 295 mass-NiO respectively The correspond-ing MgFe molar ratios in these areas are 79 and 70respectively Figure 4c and d shows other types ofserpentine microstructure ie a vein-like serpentine andan olivinendashserpentine composite In the case of vein-likestructure the particle consists of intertwined plate-likeand dense serpentine with porous serpentine in betweenThe different types of serpentine structure as well as thevariations in the compositions reflect the way thematerials formed during their weathering processes2324

Other single phase particles

Figure 5 shows examples of the microstructures ofvarious single phase particles found in the ore feedsamples Apart from the particles inside the limonitecomposite particles magnetite was also observed assingle phase particles as shown in Fig 5a Themicrostructure of the single phase particles was quitedifferent compared to magnetite inside the limonitecomposite particles They had a dense structure withsome pores and fissures this in contrast with the fineneedle-like structure observed inside the limonite com-posite particle Number 9 (quartz) was also present as aninclusion phase in the limonite composite particles andas large single phase particles as shown in Fig 5bSingle phase no 5 [chromite (spinel) particle] with densemicrostructure is shown in Fig 5c Number 5 [chromite(spinel)] has significant variations in Mg Fe and Alcompositions from one particle to another For examplethe MgO Fe2O3 and Al2O3 concentrations were foundto vary from 53 to 131 mass- 166 to 4418 mass-and 60 to 187 mass- respectively Trace proportionsof chromite particles with high concentration of Al2O3

(vary from 202 to 376 mass- with an average of274 mass-) were also observed in the sample notincluded in Table 2

Other nickel bearing minerals observed in the samplesinclude forsterite nickeloan and no 13a (FendashMn silicatecomposite) ie FendashMn silicate surrounded by MnO asshown in Fig 5d both of these phases were observed intrace concentrations and also not included in Table 2The nickel oxide concentration of the forsterite nick-eloan can be up to 280 mass- with an average of196 mass-NiO The FendashMn silicate contains a sig-nificant amount of nickel ie varying from 24 to97 mass- with an average of 71 mass-NiO Otherminerals observed in trace proportions include pyrox-ene CandashMg silicate (diopside) and gibbsite

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The major X-ray diffraction peaks in the ore feedsample are identified to be from goethite and serpentine(lizardite) as shown in Fig 2 This result supports theEPMA measurements and also shows that the majorphases present in the ore feed sample are goethite andserpentine This result combined with SEM observationand EPMA results also confirms that the fine grainno 11 (Fe rich matrix) contains mainly the goethitephase

Reduced ore sampleThe summary of the average compositions measuredusing EPMA of the major particles and phases observedin the reduced ore samples is shown in Table 3 Themajor phasesmixtures observed in the reduced oresample include Fe rich matrix (fine grain mixture ofmagnetite and silicate minerals) olivine and magnetiteOther phases observed in low quantities include quartzand chromite Minor (trace) phases observed (not shownin Table 3) include forsterite nickeloan pyroxeneserpentine CandashMg silicate FendashMgndashAl silicate gibbsiteAl rich olivine and Al rich chromite

Overview microstructures (backscattered electronimages) of the particles observed in the reduced oresample are shown in Fig 6a Similar to the ore feedsamples the majority of the coarse particles (60 ofthe total) observed in the reduced ore sample are no 1

(limonite composite particles) The bright particlesobserved in the reduced ore sample are no 3 (magne-tite) no 4 (magnetite with chromite inclusions) andno 5 (chromite) Number 8 (olivine) and no 9 (quartz)particles are also observed and appear as grey phases inthe image

Limonite composite particles

In general the composite particles in the reduced oresamples have similar characteristics to that observed inthe ore feed However more bright phases exhibiting aneedle like shape as well as porous structure withrounded shape of sizes ranging from 1 mm to tens ofmicrometres were observed in the Fe rich matrix as canbe seen in Fig 6 These bright phases correspond tomagnetite which appeared to be transformed fromgoethite upon reduction roasting

In an oxidising condition such as in air goethite istransformed to hematite (Fe2O3) upon roasting In areducing condition with very low oxygen partial pres-sure such as in the current study (pO2

~32|1015 Pa)the goethite appeared to transform to magnetite follow-ing reaction (1)

6(Fe Ni)OOH2(Fe Ni)3O4z3H2Oz1=2O2 (1)

The transformation of goethite to magnetite in thereduced ore is supported by the X-ray powder diffraction

a dense 75serpentine b 75serpentine with different Ni concentrations c 75vein-like structure d 8a5olivinendashserpentinecomposite

4 Scanning electron microscope backscattered electron micrographs showing details of different microstructures of ser-

pentine particles observed in ore feed samples

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

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Ta

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matr

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1 7

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serp

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0 5

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0 1

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20 8

0 5

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95 0

4 8

28 7

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14 1

0 3

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2 7

86 7

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netite

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eN

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35 0

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z4 5

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4

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Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 137

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

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8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

5S

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com

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com

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Fe

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30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

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(Mg

FeN

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i 2O

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H) 4

1 7

94 3

2 7

00 5

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ine

(Mg

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1 3

80 6

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95 9

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92 5

1 8

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inendashserp

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com

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1 8

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40 7

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ndashndash

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com

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8a1

serp

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(Mg

FeN

i)3S

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2 0

90 7

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Quart

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20 0

20 0

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20 1

Rhamdhani et al Nickel laterite Part 1

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

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reported to increase with decreasing particle size inboth types of ore and the addition of sulphur as pyritein the ore is reported to be beneficial to the nickelrecovery De Graaf also suggested that unextractablenickel in saprolitic ore is associated with the formationof recrystallised olivine (Mg2SiO4) or enstatite(MgSiO3) in the reduced ore as had been inferred byHayashi14

Valix and Cheung1516 using synchrotron radiationX-ray powder diffraction technique studied the phasetransformation of precalcined laterite ores during hightemperature reduction in COCO2 gas mixtures at fixedratios In the case of limonite ore they reported that theoptimum Ni recovery was obtained when the orereduction was carried out at 600uC The X-ray diffrac-tion spectra indicated that under reducing conditionsgoethite in the limonite ore was transformed tomagnetite at 400uC The X-ray spectra also indicatedthe formation of iron nickel alloy (taenite) however attemperatures 700uC they observed a significantdecrease in the alloy X-ray peaks In the case ofreduction of precalcined saprolitic ore they observedthe transformation of serpentine to forsterite olivine(2MgOSiO2) at 700uC This however was not observedwhen the reducing gas was introduced before thedehydroxylation of serpentine instead fayalite olivine(2FeOSiO2) was formed The addition of sulphur wasreported to suppress the formation of forsterite duringreduction roasting of the saprolite

None of the studies412ndash19 described above provideinformation on the changes on the microstructure andnickel distribution in the phases at microscopic level as aresult of the reduction and leaching only limitedinformation can be found in literature20ndash22

During the reduction roasting and leaching complexchanges in the materialsrsquo microstructure phase nickeldistribution and other characteristics are occurringUnderstanding these changes is important not onlyfrom the point of view of understanding the underlyingscience but also for improved control of technologicalapplications as they strongly affect the overall nickelrecovery from the ore

The principal aims of the current studies are toprovide detailed quantitative information on micro-structure phase and nickel distribution changes and toevaluate the thermodynamic of the reduction roastingin support of increasing Ni recovery in industrialoperations The approach taken in the current studiesis to

(i) systematically characterise (using various techni-ques) the processed laterites obtained fromindustrial operations

(ii) reconcile these results to provide quantitativedescriptions of the materials

(iii) relate this information with the thermodynamicand phase change analysis of the materials tocharacterise the important reactions taking placeduring the processes and to identify importantoperation parameters influencing Ni recovery

In Part 1 of this series of papers microstructure andphase characterisation results including the Ni distribu-tion on the phases present in the laterite processed in theplant are reported The analyses of the microstructureand thermodynamic of phase changes in the materialsare described in Part 2 of the series

Experimental

MaterialsNickel laterite samples used in the study were suppliedby BHP Billiton Yabulu refinery and were obtainedfrom various locations in the plant5 these include

(i) ore feed ie processed ore feed to multiplehearth roasters

(ii) reduced ore ie ore from the exit of a coolerafter multiple hearth roasters

(iii) leached ore ie residue from the leaching carriedout in laboratory

Process conditionsThe nickel laterite ore used was a mixture of limoniticand saprolitic ores (of approximately 70ndash30 mass-)imported from New Caledonia Indonesia andPhilippines In the process the mixture was fed torotary driers and then to ball mills where they wereground to fine powders The fine ores were then mixedwith fuel oil reductant and reduction roasted in multiplehearth roasters to a maximum temperature of 740uCunder a reducing condition The reducing conditionsachieved in the reactor were a result of partialcombustion of fuel oil and supplementary hydrogenadded to the hearths From thermodynamic calculationsand mass balancing of gas components of the input andoutput streams of the reactor the effective oxygenpartial pressure pO2

inside the reactor was estimated tobe 32610215 Pa (102195 atm) The ores exited themultiple hearth roasters at 680uC and were directlycooled in rotary ore coolers under reducing conditionsbefore quenched into an ammonium carbonate aqueoussolution

In the current study leaching of the reduced ore wascarried out in laboratory The leaching tests were carriedout in cylindrical vessels in 561024 m3 of ammoniacalsolution (consisting of 80 kg m23 NH3 70 kg m23

CO2 and 1 kg m23 Na2EDTA) Ethylene diamine tetraacetic acid (EDTA) was added into the leaching solutionwith the purpose of avoiding the formation of ferrichydroxide precipitate that may affect the concentrationof dissolved metals in the leaching solution To simulateindustrial conditions the leaching tests were carried outin two stages First the slurry was aerobically leached forone hour at ambient temperature and 116761025 m3 s21 air the air was first sparged through561024 m3 of aqua ammonia before introduction tothe leach After aerobic leaching the slurry was vacuumfiltered and subsequently leached anaerobically in261024 m3 of fresh leaching liquor for three days at40uC After anaerobic leaching the slurry was vacuumfiltered and dried at 110uC to obtain the leached oresamples

Analysis techniques and sample preparationElectron probe X-ray microanalyses were carried outusing Superprobe JEOL 8200L (JEOL Ltd TokyoJapan) equipped with five wavelength dispersive detec-tors The EPMA was operated at 15 kV acceleratingvoltage and probe current of 15 nA Standards (MgOquartz SiO2 hematite Fe2O3 chromite FeCr2O4 Al2O3

and NiO from Charles M Taylor Co Stanford CA)were used for the calibration of the EPMA measure-ments In addition to the EPMA analyses scanningelectron microscopy (SEM) observations were carried

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out using Phillips XL-30 (Phillips FEI CompanyHillsboro OR) and cold field emission JEOL 63006400 with accelerating voltages 15 and 20 kV respec-tively Elemental bulk analysis of the samples wascarried out using the inductively coupled plasma atomicemission spectroscopy technique Bulk sulphur andcarbon compositions of the samples were analysed usingLECO CS-444C-S (LECO Corp St Joseph MI)

To enable the examination of mineral sections the oresamples were mounted in epoxy resin and cured in avacuum chamber Cross-sections of the samples werethen prepared by polishing using SiC paper anddiamond paste (down to a 025 mm size) After cleaningthe mounted samples were then sputter coated withcarbon or platinum using Eiko IB-5 Sputter Coater(Eiko Co Ltd Hitachinaka Japan) For SEM surfacemorphology observations the powder samples after theexperiments were directly placed on a carbon tabattached to an aluminium pin stub before being sputtercoated with carbon or platinum

Synchrotron radiation based X-ray powder diffrac-tion (SXRD) analysis was carried out on the BigDiffpowder XRD beamline at the Australian NationalBeamline Facility at the Photon Factory TsukubaJapan Approximately 1024 kg subsample of the oreswere mixed with 10 mass- NIST 640C Si standard thenground using an agate mortar and pestle under ethanolfor 5 min before experiments X-ray wavelengths of08 A and current of 400 mA were used in the analysesThe exposure time was 20 min per sample

The particle size distributions were measured usingMastersizer 2000 (Malvern Instruments LtdWorchestershire UK)

The approach taken in reconciling the data in thecurrent study is as follows

(i) EPMA analysis was used to characterise thecompositions of the phasesparticles The aver-age compositions of the phasesparticles reportedin the current study were calculated from EPMAanalysis of at least 20 points from similar phasesparticles

(ii) the proportions of these phasesparticles inthe ore samples were determined by estimatingthe area percentage of each phaseparticle on theSEM images of the ore samplesrsquo sections using

image analysis software The results were cross-checked through mass balance considering theEPMA measurements and inductively coupledplasma atomic emission spectroscopy bulk com-position analyses

(iii) the distribution of elements in particular Nibetween phases was determined by multiplyingthe estimated phase proportion by the averageconcentration of elements in that particularphaseparticle measured by EPMA

Results and discussion

Bulk composition particle size distribution andsynchrotron XRD resultsThe elemental bulk compositions of the ore feedreduced ore and leached ore samples are given inTable 1 The corresponding compositions of the orefeed reduced ore and leached ore samples recalculatedto oxides and their normalised values given in bracketsare also shown The normalised values were calculatedby dividing the mass- of individual oxide by the totalmass- of metal oxides and multiplying by 100 It canbe seen from Table 1 that the major components in theores are iron silicon and magnesium

The particle size distributions of the ore feed reducedore and leached ore samples are shown in Fig 1 The orefeed consists of particles with size varying from 02 to700 mm with mean particle size of 21 mm About23 vol- of the materials have a size 5 mm and only6 vol- are 100 mm

Table 1 Bulk elemental and their corresponding oxide compositions of dried ore feed reduced ore and leached oresamples (values in bracket are normalised)

ElementsOre feedmass-

Reduced oremass-

Leached oremass- Oxides

Ore feedmass-

Reduced oremass-

Leached oremass-

Al 183 207 216 Al2O3 346 (402) 391 (403) 408 (416)Ca 021 026 026 CaO 029 (034) 036 (037) 036 (037)C 033 123 139 C 033 (038) 123 (127) 139 (142)Cr 155 169 158 Cr2O3 227 (263) 247 (254) 231 (235)Co 014 014 005 CoO 018 (020) 018 (019) 006 (006)Fe 332 350 372 Fe2O3 4746 (5515) 5004 (5152) 5318 (5414)Mg 565 709 680 MgO 937 (1089) 1176 (1211) 1128 (1148)Mn 074 076 068 MnO 096 (111) 098 (101) 088 (089)Ni 161 179 038 NiO 205 (238) 228 (235) 048 (049)K 002 005 005 K2O 002 (003) 006 (006) 006 (006)Si 909 1089 1109 SiO2 1944 (2259) 2329 (2398) 2372 (2415)Na 002 004 004 Na2O 003 (003) 005 (006) 005 (005)S 011 040 025 S 011 040 025Ti 004 004 005 TiO2 006 (007) 007 (008) 008 (008)Zn 002 002 002 ZnO 003 (003) 003 (003) 003 (003)Sum 5456 6148 6200 Sum 8606 (100) 9712 (100) 9823 (100)

1 Particle size distributions of ore feed reduced ore and

leached ore samples

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There was a change in the particle size distribution ofthe ore samples upon reduction roasting as shown inFig 1 The distribution was shifted to the right themean particle size of the sample was increased from 21to 43 mm The volume percentage of particles with asize larger than 100 mm in ore was increased from 6 to13 vol- The changes in the distribution were mainlyassociated with the agglomeration of the materials uponreduction roasting

The mean particle size of the leached ore sample was35 mm smaller than that of reduced ore ie 43 mm Itcan also be seen from Fig 1 that the distribution isslightly shifted to the left The volume percentage ofparticles with a size 100 mm in the leached ore samplesis 57 vol-

Synchrotron X-ray powder diffraction analyses werecarried out on the ore feed reduced ore and leached oresamples to identify the crystalline phases present in thematerials The resultant SXRD spectra are shown inFig 2 It can be seen that in the case of ore feed samplethe major peaks present are identified to be from

goethite [(FeNi)O(OH)] serpentine-lizardite[(MgFeNi)3Si2O5(OH)4 quartz SiO2] and spinel Fe-chromite [(FeMg)O(Cr Al Fe)2O3] The peaksobserved in the reduced ore sample are of olivine[(MgFeNi)2SiO4] magnetite [(FeNi)OFe2O3] quartzspinel Fe chromite and taenite (FeNi) alloy The peaksobserved in the leached ore are similar as in the reducedore however the peaks of taenite do not appearconfirming the nickel dissolution upon leaching

Ore feed sampleTable 2 shows the summary of the average compositionsof the particles and phases observed in the ore feedsamples measured using EPMA The results arepresented in terms of oxides composition (mass-) andare average values of multiple measurements conductedon a number of similar particlesphases The composi-tions presented are normalised values It should be notedthat in the case of goethite (and fine grained matrix) andserpentine the total counts of the EPMA measurementare 100 due to the present of water of crystal-lisation For simplicity only particles with a proportion1 are reported Trace elements observed in eachphases such as Ca Mn Cu Ti Na K Zn Pb and Coare also not reported

The approximate proportions of the various particles(mass-) in the sample as well as the relative propor-tions (on average) of phases present in each observedparticle are also presented in Table 2 (in columns 2 and5 respectively) These compositions were approximatedby reconciling mass balance using the results of EPMAmeasurements SEM observations and chemical bulkanalysis (Table 1)

Figure 3a shows an example of an SEM image(backscattered electron image) of the ore feed sampleat low magnification showing the general microstruc-ture of the particles The greyscale in the image showsthe relative mean atomic number of the material thusrepresenting differences in compositions The numberson the images were assigned to represent a particularparticle type or phase according to Table 2 In generalcomplex structures such as composite intergrowthvein-likeplate-like porous and dense structures wereobserved in the particles in the ore feed sample

2 Synchrotron X-ray powder diffraction spectra (synchro-

tron radiation wavelength 08 A) of nickel laterite ore

feed reduced ore and leached ore samples [L lizardite

(serpentine) G goethite Q quartz Si silicon stan-

dard O olivine M magnetite S spinel (Fendashchromite)

T taenite (FendashNi alloy)]

1 limonite composite particle 3 magnetite 5 chromite 7 serpentine 9 quartz 11 Fe rich matrix 12 goethite 13magnetite 17 serpentine

3 Scanning electron microscope backscattered electron micrographs of ore feed samples showing a overview of micro-

structures of particles and b detailed microstructure of limonite composite particle (no 1 in a)

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Ta

ble

2S

um

ma

ryo

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ite

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ine

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50 0

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oliv

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50 0

0 5

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Quart

z3 0

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2100 0

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l100

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9

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 133

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In the current discussion the ore particles wereclassified into two categories ie single phase andcomposite particles The single phase particle refers toa particle that consists of only a single phase (with orwithout small amount of inclusions) The compositeparticle in this case refers to agglomerated particles withvarious phases embedded in a matrix or a blend(intergrowth) between two or more phases or mineralgrains

It can be seen from Table 2 that the major phasesmixtures observed in the ore feed sample include Fe richmatrix (a fine grain mixture of goethite and silicateminerals) goethite and serpentine Other phasesobserved include quartz olivine magnetite and chro-mite Trace phases (not included in Table 2) observedinclude CandashMg silicate (diopside) forsterite nickeloan(NiO2MgO4SiO2) FendashMn silicate pyroxene[(MgCaFeNi)SiO3] and gibbsite [Al(OH)3] In thecurrent study general mineral species names werereported no attempts were made to distinguish theprecise mineral species

Limonite composite particles

The majority of the coarse particles 60 mass- of thetotal ore sample were limonite composite particles ieparticles consisting of fine grains of Fe rich mineralmatrix with inclusion phases embedded in it (labelledno 1 in Fig 3a) The limonite composite particles inaverage contain of 70 of Fe rich matrix and 30 ofother phasegrain inclusions Most of these limonitecomposite particles have sizes in the range of hundredsof micrometres The remainder of the coarse particleswere no 7 (serpentine 26 mass-) and other singlephase particles such as no 3 (magnetite) no 5 (chro-mite) and no 9 (quartz) as shown in Fig 3a Magnetiteand chromite phases appear bright in the backscatteredelectron images and others appear as darker grey phases

Figure 3b shows in more detail the limonite compositeparticle This particular composite consists of smallergrainsphases of no 12 (goethite) no 13 (magnetiteappear as bright phases) and no 17 (serpentine)embedded in no 11 (Fe rich matrix) The inclusionphasesgrains in the matrix have different types ofmorphology such as needle-like plate-like and roundshapes with a size ranging from 1 mm to tens ofmicrometres

The matrix of the limonite composite particlesconsists mainly of Fe and other elements such as SiMg and Al in lower concentrations Considering thelarge concentration of the matrix in the ore feedsamples and by reconciling with X-ray powder diffrac-tion analysis results it was concluded that this matrixmainly consists of a mixture of fine grained goethite withsilicate minerals ie serpentine

There were variations in composition in the fine grainmatrix between particles and within a particle Thenickel oxide concentration in the matrix was found tovary from about 005ndash to 620 mass- In the particle inFig 3b the average nickel oxide concentration in thematrix was 214 mass- For comparison the nickeloxide concentration of no 12 (goethite) inside thelimonite composite particles was 142 mass- onaverage It should be noted that no separate NiO orCoO particles were observed The clear indications fromthe analyses are that the Ni and Co are present in dilute

solid solution mostly in the goethite magnetite serpen-tine and olivine crystal lattice

Serpentine particles

Serpentine was present as a single phase (dense orporous) particles as well as composite particlesexamples of these microstructures are shown in Fig 4There were variations in composition between serpen-tine particles (in terms of MgFe ratio and mass-NiO)and within a particle in some of the serpentine iedemonstrated by two or more different grey regionsInclusions (such as magnetite) may also be present insidethese serpentine particles Figure 4a shows a singlephase large serpentine particle with dense morphology(a particle size of 500 mm) A single phase serpentineparticle with two different grey areas is shown in Fig 4bIn this particular particle the light grey area has a lowernickel oxide concentration compared to the darker area162 and 295 mass-NiO respectively The correspond-ing MgFe molar ratios in these areas are 79 and 70respectively Figure 4c and d shows other types ofserpentine microstructure ie a vein-like serpentine andan olivinendashserpentine composite In the case of vein-likestructure the particle consists of intertwined plate-likeand dense serpentine with porous serpentine in betweenThe different types of serpentine structure as well as thevariations in the compositions reflect the way thematerials formed during their weathering processes2324

Other single phase particles

Figure 5 shows examples of the microstructures ofvarious single phase particles found in the ore feedsamples Apart from the particles inside the limonitecomposite particles magnetite was also observed assingle phase particles as shown in Fig 5a Themicrostructure of the single phase particles was quitedifferent compared to magnetite inside the limonitecomposite particles They had a dense structure withsome pores and fissures this in contrast with the fineneedle-like structure observed inside the limonite com-posite particle Number 9 (quartz) was also present as aninclusion phase in the limonite composite particles andas large single phase particles as shown in Fig 5bSingle phase no 5 [chromite (spinel) particle] with densemicrostructure is shown in Fig 5c Number 5 [chromite(spinel)] has significant variations in Mg Fe and Alcompositions from one particle to another For examplethe MgO Fe2O3 and Al2O3 concentrations were foundto vary from 53 to 131 mass- 166 to 4418 mass-and 60 to 187 mass- respectively Trace proportionsof chromite particles with high concentration of Al2O3

(vary from 202 to 376 mass- with an average of274 mass-) were also observed in the sample notincluded in Table 2

Other nickel bearing minerals observed in the samplesinclude forsterite nickeloan and no 13a (FendashMn silicatecomposite) ie FendashMn silicate surrounded by MnO asshown in Fig 5d both of these phases were observed intrace concentrations and also not included in Table 2The nickel oxide concentration of the forsterite nick-eloan can be up to 280 mass- with an average of196 mass-NiO The FendashMn silicate contains a sig-nificant amount of nickel ie varying from 24 to97 mass- with an average of 71 mass-NiO Otherminerals observed in trace proportions include pyrox-ene CandashMg silicate (diopside) and gibbsite

Rhamdhani et al Nickel laterite Part 1

134 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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The major X-ray diffraction peaks in the ore feedsample are identified to be from goethite and serpentine(lizardite) as shown in Fig 2 This result supports theEPMA measurements and also shows that the majorphases present in the ore feed sample are goethite andserpentine This result combined with SEM observationand EPMA results also confirms that the fine grainno 11 (Fe rich matrix) contains mainly the goethitephase

Reduced ore sampleThe summary of the average compositions measuredusing EPMA of the major particles and phases observedin the reduced ore samples is shown in Table 3 Themajor phasesmixtures observed in the reduced oresample include Fe rich matrix (fine grain mixture ofmagnetite and silicate minerals) olivine and magnetiteOther phases observed in low quantities include quartzand chromite Minor (trace) phases observed (not shownin Table 3) include forsterite nickeloan pyroxeneserpentine CandashMg silicate FendashMgndashAl silicate gibbsiteAl rich olivine and Al rich chromite

Overview microstructures (backscattered electronimages) of the particles observed in the reduced oresample are shown in Fig 6a Similar to the ore feedsamples the majority of the coarse particles (60 ofthe total) observed in the reduced ore sample are no 1

(limonite composite particles) The bright particlesobserved in the reduced ore sample are no 3 (magne-tite) no 4 (magnetite with chromite inclusions) andno 5 (chromite) Number 8 (olivine) and no 9 (quartz)particles are also observed and appear as grey phases inthe image

Limonite composite particles

In general the composite particles in the reduced oresamples have similar characteristics to that observed inthe ore feed However more bright phases exhibiting aneedle like shape as well as porous structure withrounded shape of sizes ranging from 1 mm to tens ofmicrometres were observed in the Fe rich matrix as canbe seen in Fig 6 These bright phases correspond tomagnetite which appeared to be transformed fromgoethite upon reduction roasting

In an oxidising condition such as in air goethite istransformed to hematite (Fe2O3) upon roasting In areducing condition with very low oxygen partial pres-sure such as in the current study (pO2

~32|1015 Pa)the goethite appeared to transform to magnetite follow-ing reaction (1)

6(Fe Ni)OOH2(Fe Ni)3O4z3H2Oz1=2O2 (1)

The transformation of goethite to magnetite in thereduced ore is supported by the X-ray powder diffraction

a dense 75serpentine b 75serpentine with different Ni concentrations c 75vein-like structure d 8a5olivinendashserpentinecomposite

4 Scanning electron microscope backscattered electron micrographs showing details of different microstructures of ser-

pentine particles observed in ore feed samples

Rhamdhani et al Nickel laterite Part 1

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

3S

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mass-

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limonite

com

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matr

ix71 7

43 0

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152 8

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317 0

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g)O

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1 7

1 0

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0 6

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0 1

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serp

entine

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0 5

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2 0

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20 5

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ine

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a

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0 9

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0 4

2 0

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80 7

1 8

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0 1

0 1

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4 5

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20 8

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86 5

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2 8

0 5

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5 0

0 0

9 7

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54 8

11 8

0 0

40 0

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g)O

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100 0

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0 0

70 1

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ine

18 5

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ine

8

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100 0

18 5

38 8

46 9

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0 5

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44 8

8 9

0 5

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2 3

83 6

8a2

serp

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FeN

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H) 4

40 0

2 0

28 6

48 2

6 8

0 3

0 6

2 3

32 4

5 0

08b

oliv

ine

with

mag

netite

inclu

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ns

8b

1

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95 0

4 8

28 7

44 4

14 1

0 3

0 5

2 7

86 7

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

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quart

z

SiO

2100 0

4 5

0 3

98 2

1 1

0 0

0 1

0 0

70 2

0 0

0Tota

l100

100

1 5

4

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 137

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

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Ltd

reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

140 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

xim

ate

pro

po

rtio

no

fto

tal

mass-

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ap

pro

xim

ate

pro

po

rtio

nin

part

icle

s

Ap

pro

xim

ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

posite

33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

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ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

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ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

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fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

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144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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out using Phillips XL-30 (Phillips FEI CompanyHillsboro OR) and cold field emission JEOL 63006400 with accelerating voltages 15 and 20 kV respec-tively Elemental bulk analysis of the samples wascarried out using the inductively coupled plasma atomicemission spectroscopy technique Bulk sulphur andcarbon compositions of the samples were analysed usingLECO CS-444C-S (LECO Corp St Joseph MI)

To enable the examination of mineral sections the oresamples were mounted in epoxy resin and cured in avacuum chamber Cross-sections of the samples werethen prepared by polishing using SiC paper anddiamond paste (down to a 025 mm size) After cleaningthe mounted samples were then sputter coated withcarbon or platinum using Eiko IB-5 Sputter Coater(Eiko Co Ltd Hitachinaka Japan) For SEM surfacemorphology observations the powder samples after theexperiments were directly placed on a carbon tabattached to an aluminium pin stub before being sputtercoated with carbon or platinum

Synchrotron radiation based X-ray powder diffrac-tion (SXRD) analysis was carried out on the BigDiffpowder XRD beamline at the Australian NationalBeamline Facility at the Photon Factory TsukubaJapan Approximately 1024 kg subsample of the oreswere mixed with 10 mass- NIST 640C Si standard thenground using an agate mortar and pestle under ethanolfor 5 min before experiments X-ray wavelengths of08 A and current of 400 mA were used in the analysesThe exposure time was 20 min per sample

The particle size distributions were measured usingMastersizer 2000 (Malvern Instruments LtdWorchestershire UK)

The approach taken in reconciling the data in thecurrent study is as follows

(i) EPMA analysis was used to characterise thecompositions of the phasesparticles The aver-age compositions of the phasesparticles reportedin the current study were calculated from EPMAanalysis of at least 20 points from similar phasesparticles

(ii) the proportions of these phasesparticles inthe ore samples were determined by estimatingthe area percentage of each phaseparticle on theSEM images of the ore samplesrsquo sections using

image analysis software The results were cross-checked through mass balance considering theEPMA measurements and inductively coupledplasma atomic emission spectroscopy bulk com-position analyses

(iii) the distribution of elements in particular Nibetween phases was determined by multiplyingthe estimated phase proportion by the averageconcentration of elements in that particularphaseparticle measured by EPMA

Results and discussion

Bulk composition particle size distribution andsynchrotron XRD resultsThe elemental bulk compositions of the ore feedreduced ore and leached ore samples are given inTable 1 The corresponding compositions of the orefeed reduced ore and leached ore samples recalculatedto oxides and their normalised values given in bracketsare also shown The normalised values were calculatedby dividing the mass- of individual oxide by the totalmass- of metal oxides and multiplying by 100 It canbe seen from Table 1 that the major components in theores are iron silicon and magnesium

The particle size distributions of the ore feed reducedore and leached ore samples are shown in Fig 1 The orefeed consists of particles with size varying from 02 to700 mm with mean particle size of 21 mm About23 vol- of the materials have a size 5 mm and only6 vol- are 100 mm

Table 1 Bulk elemental and their corresponding oxide compositions of dried ore feed reduced ore and leached oresamples (values in bracket are normalised)

ElementsOre feedmass-

Reduced oremass-

Leached oremass- Oxides

Ore feedmass-

Reduced oremass-

Leached oremass-

Al 183 207 216 Al2O3 346 (402) 391 (403) 408 (416)Ca 021 026 026 CaO 029 (034) 036 (037) 036 (037)C 033 123 139 C 033 (038) 123 (127) 139 (142)Cr 155 169 158 Cr2O3 227 (263) 247 (254) 231 (235)Co 014 014 005 CoO 018 (020) 018 (019) 006 (006)Fe 332 350 372 Fe2O3 4746 (5515) 5004 (5152) 5318 (5414)Mg 565 709 680 MgO 937 (1089) 1176 (1211) 1128 (1148)Mn 074 076 068 MnO 096 (111) 098 (101) 088 (089)Ni 161 179 038 NiO 205 (238) 228 (235) 048 (049)K 002 005 005 K2O 002 (003) 006 (006) 006 (006)Si 909 1089 1109 SiO2 1944 (2259) 2329 (2398) 2372 (2415)Na 002 004 004 Na2O 003 (003) 005 (006) 005 (005)S 011 040 025 S 011 040 025Ti 004 004 005 TiO2 006 (007) 007 (008) 008 (008)Zn 002 002 002 ZnO 003 (003) 003 (003) 003 (003)Sum 5456 6148 6200 Sum 8606 (100) 9712 (100) 9823 (100)

1 Particle size distributions of ore feed reduced ore and

leached ore samples

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There was a change in the particle size distribution ofthe ore samples upon reduction roasting as shown inFig 1 The distribution was shifted to the right themean particle size of the sample was increased from 21to 43 mm The volume percentage of particles with asize larger than 100 mm in ore was increased from 6 to13 vol- The changes in the distribution were mainlyassociated with the agglomeration of the materials uponreduction roasting

The mean particle size of the leached ore sample was35 mm smaller than that of reduced ore ie 43 mm Itcan also be seen from Fig 1 that the distribution isslightly shifted to the left The volume percentage ofparticles with a size 100 mm in the leached ore samplesis 57 vol-

Synchrotron X-ray powder diffraction analyses werecarried out on the ore feed reduced ore and leached oresamples to identify the crystalline phases present in thematerials The resultant SXRD spectra are shown inFig 2 It can be seen that in the case of ore feed samplethe major peaks present are identified to be from

goethite [(FeNi)O(OH)] serpentine-lizardite[(MgFeNi)3Si2O5(OH)4 quartz SiO2] and spinel Fe-chromite [(FeMg)O(Cr Al Fe)2O3] The peaksobserved in the reduced ore sample are of olivine[(MgFeNi)2SiO4] magnetite [(FeNi)OFe2O3] quartzspinel Fe chromite and taenite (FeNi) alloy The peaksobserved in the leached ore are similar as in the reducedore however the peaks of taenite do not appearconfirming the nickel dissolution upon leaching

Ore feed sampleTable 2 shows the summary of the average compositionsof the particles and phases observed in the ore feedsamples measured using EPMA The results arepresented in terms of oxides composition (mass-) andare average values of multiple measurements conductedon a number of similar particlesphases The composi-tions presented are normalised values It should be notedthat in the case of goethite (and fine grained matrix) andserpentine the total counts of the EPMA measurementare 100 due to the present of water of crystal-lisation For simplicity only particles with a proportion1 are reported Trace elements observed in eachphases such as Ca Mn Cu Ti Na K Zn Pb and Coare also not reported

The approximate proportions of the various particles(mass-) in the sample as well as the relative propor-tions (on average) of phases present in each observedparticle are also presented in Table 2 (in columns 2 and5 respectively) These compositions were approximatedby reconciling mass balance using the results of EPMAmeasurements SEM observations and chemical bulkanalysis (Table 1)

Figure 3a shows an example of an SEM image(backscattered electron image) of the ore feed sampleat low magnification showing the general microstruc-ture of the particles The greyscale in the image showsthe relative mean atomic number of the material thusrepresenting differences in compositions The numberson the images were assigned to represent a particularparticle type or phase according to Table 2 In generalcomplex structures such as composite intergrowthvein-likeplate-like porous and dense structures wereobserved in the particles in the ore feed sample

2 Synchrotron X-ray powder diffraction spectra (synchro-

tron radiation wavelength 08 A) of nickel laterite ore

feed reduced ore and leached ore samples [L lizardite

(serpentine) G goethite Q quartz Si silicon stan-

dard O olivine M magnetite S spinel (Fendashchromite)

T taenite (FendashNi alloy)]

1 limonite composite particle 3 magnetite 5 chromite 7 serpentine 9 quartz 11 Fe rich matrix 12 goethite 13magnetite 17 serpentine

3 Scanning electron microscope backscattered electron micrographs of ore feed samples showing a overview of micro-

structures of particles and b detailed microstructure of limonite composite particle (no 1 in a)

Rhamdhani et al Nickel laterite Part 1

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Ta

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22 0

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9

Rhamdhani et al Nickel laterite Part 1

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In the current discussion the ore particles wereclassified into two categories ie single phase andcomposite particles The single phase particle refers toa particle that consists of only a single phase (with orwithout small amount of inclusions) The compositeparticle in this case refers to agglomerated particles withvarious phases embedded in a matrix or a blend(intergrowth) between two or more phases or mineralgrains

It can be seen from Table 2 that the major phasesmixtures observed in the ore feed sample include Fe richmatrix (a fine grain mixture of goethite and silicateminerals) goethite and serpentine Other phasesobserved include quartz olivine magnetite and chro-mite Trace phases (not included in Table 2) observedinclude CandashMg silicate (diopside) forsterite nickeloan(NiO2MgO4SiO2) FendashMn silicate pyroxene[(MgCaFeNi)SiO3] and gibbsite [Al(OH)3] In thecurrent study general mineral species names werereported no attempts were made to distinguish theprecise mineral species

Limonite composite particles

The majority of the coarse particles 60 mass- of thetotal ore sample were limonite composite particles ieparticles consisting of fine grains of Fe rich mineralmatrix with inclusion phases embedded in it (labelledno 1 in Fig 3a) The limonite composite particles inaverage contain of 70 of Fe rich matrix and 30 ofother phasegrain inclusions Most of these limonitecomposite particles have sizes in the range of hundredsof micrometres The remainder of the coarse particleswere no 7 (serpentine 26 mass-) and other singlephase particles such as no 3 (magnetite) no 5 (chro-mite) and no 9 (quartz) as shown in Fig 3a Magnetiteand chromite phases appear bright in the backscatteredelectron images and others appear as darker grey phases

Figure 3b shows in more detail the limonite compositeparticle This particular composite consists of smallergrainsphases of no 12 (goethite) no 13 (magnetiteappear as bright phases) and no 17 (serpentine)embedded in no 11 (Fe rich matrix) The inclusionphasesgrains in the matrix have different types ofmorphology such as needle-like plate-like and roundshapes with a size ranging from 1 mm to tens ofmicrometres

The matrix of the limonite composite particlesconsists mainly of Fe and other elements such as SiMg and Al in lower concentrations Considering thelarge concentration of the matrix in the ore feedsamples and by reconciling with X-ray powder diffrac-tion analysis results it was concluded that this matrixmainly consists of a mixture of fine grained goethite withsilicate minerals ie serpentine

There were variations in composition in the fine grainmatrix between particles and within a particle Thenickel oxide concentration in the matrix was found tovary from about 005ndash to 620 mass- In the particle inFig 3b the average nickel oxide concentration in thematrix was 214 mass- For comparison the nickeloxide concentration of no 12 (goethite) inside thelimonite composite particles was 142 mass- onaverage It should be noted that no separate NiO orCoO particles were observed The clear indications fromthe analyses are that the Ni and Co are present in dilute

solid solution mostly in the goethite magnetite serpen-tine and olivine crystal lattice

Serpentine particles

Serpentine was present as a single phase (dense orporous) particles as well as composite particlesexamples of these microstructures are shown in Fig 4There were variations in composition between serpen-tine particles (in terms of MgFe ratio and mass-NiO)and within a particle in some of the serpentine iedemonstrated by two or more different grey regionsInclusions (such as magnetite) may also be present insidethese serpentine particles Figure 4a shows a singlephase large serpentine particle with dense morphology(a particle size of 500 mm) A single phase serpentineparticle with two different grey areas is shown in Fig 4bIn this particular particle the light grey area has a lowernickel oxide concentration compared to the darker area162 and 295 mass-NiO respectively The correspond-ing MgFe molar ratios in these areas are 79 and 70respectively Figure 4c and d shows other types ofserpentine microstructure ie a vein-like serpentine andan olivinendashserpentine composite In the case of vein-likestructure the particle consists of intertwined plate-likeand dense serpentine with porous serpentine in betweenThe different types of serpentine structure as well as thevariations in the compositions reflect the way thematerials formed during their weathering processes2324

Other single phase particles

Figure 5 shows examples of the microstructures ofvarious single phase particles found in the ore feedsamples Apart from the particles inside the limonitecomposite particles magnetite was also observed assingle phase particles as shown in Fig 5a Themicrostructure of the single phase particles was quitedifferent compared to magnetite inside the limonitecomposite particles They had a dense structure withsome pores and fissures this in contrast with the fineneedle-like structure observed inside the limonite com-posite particle Number 9 (quartz) was also present as aninclusion phase in the limonite composite particles andas large single phase particles as shown in Fig 5bSingle phase no 5 [chromite (spinel) particle] with densemicrostructure is shown in Fig 5c Number 5 [chromite(spinel)] has significant variations in Mg Fe and Alcompositions from one particle to another For examplethe MgO Fe2O3 and Al2O3 concentrations were foundto vary from 53 to 131 mass- 166 to 4418 mass-and 60 to 187 mass- respectively Trace proportionsof chromite particles with high concentration of Al2O3

(vary from 202 to 376 mass- with an average of274 mass-) were also observed in the sample notincluded in Table 2

Other nickel bearing minerals observed in the samplesinclude forsterite nickeloan and no 13a (FendashMn silicatecomposite) ie FendashMn silicate surrounded by MnO asshown in Fig 5d both of these phases were observed intrace concentrations and also not included in Table 2The nickel oxide concentration of the forsterite nick-eloan can be up to 280 mass- with an average of196 mass-NiO The FendashMn silicate contains a sig-nificant amount of nickel ie varying from 24 to97 mass- with an average of 71 mass-NiO Otherminerals observed in trace proportions include pyrox-ene CandashMg silicate (diopside) and gibbsite

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The major X-ray diffraction peaks in the ore feedsample are identified to be from goethite and serpentine(lizardite) as shown in Fig 2 This result supports theEPMA measurements and also shows that the majorphases present in the ore feed sample are goethite andserpentine This result combined with SEM observationand EPMA results also confirms that the fine grainno 11 (Fe rich matrix) contains mainly the goethitephase

Reduced ore sampleThe summary of the average compositions measuredusing EPMA of the major particles and phases observedin the reduced ore samples is shown in Table 3 Themajor phasesmixtures observed in the reduced oresample include Fe rich matrix (fine grain mixture ofmagnetite and silicate minerals) olivine and magnetiteOther phases observed in low quantities include quartzand chromite Minor (trace) phases observed (not shownin Table 3) include forsterite nickeloan pyroxeneserpentine CandashMg silicate FendashMgndashAl silicate gibbsiteAl rich olivine and Al rich chromite

Overview microstructures (backscattered electronimages) of the particles observed in the reduced oresample are shown in Fig 6a Similar to the ore feedsamples the majority of the coarse particles (60 ofthe total) observed in the reduced ore sample are no 1

(limonite composite particles) The bright particlesobserved in the reduced ore sample are no 3 (magne-tite) no 4 (magnetite with chromite inclusions) andno 5 (chromite) Number 8 (olivine) and no 9 (quartz)particles are also observed and appear as grey phases inthe image

Limonite composite particles

In general the composite particles in the reduced oresamples have similar characteristics to that observed inthe ore feed However more bright phases exhibiting aneedle like shape as well as porous structure withrounded shape of sizes ranging from 1 mm to tens ofmicrometres were observed in the Fe rich matrix as canbe seen in Fig 6 These bright phases correspond tomagnetite which appeared to be transformed fromgoethite upon reduction roasting

In an oxidising condition such as in air goethite istransformed to hematite (Fe2O3) upon roasting In areducing condition with very low oxygen partial pres-sure such as in the current study (pO2

~32|1015 Pa)the goethite appeared to transform to magnetite follow-ing reaction (1)

6(Fe Ni)OOH2(Fe Ni)3O4z3H2Oz1=2O2 (1)

The transformation of goethite to magnetite in thereduced ore is supported by the X-ray powder diffraction

a dense 75serpentine b 75serpentine with different Ni concentrations c 75vein-like structure d 8a5olivinendashserpentinecomposite

4 Scanning electron microscope backscattered electron micrographs showing details of different microstructures of ser-

pentine particles observed in ore feed samples

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

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Ta

ble

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60 0

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1 1

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rich

matr

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43 0

2 3

6 8

73 1

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152 8

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317 0

10 2

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2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

z9

quart

z

SiO

2100 0

4 5

0 3

98 2

1 1

0 0

0 1

0 0

70 2

0 0

0Tota

l100

100

1 5

4

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 137

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

Rhamdhani et al Nickel laterite Part 1

138 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

Rhamdhani et al Nickel laterite Part 1

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

140 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

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ate

pro

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mass-

Part

icle

Ph

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lg

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e

Ap

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part

icle

s

Ap

pro

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mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

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part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

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33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

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com

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34 1

1

serp

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0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

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Ta

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by

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do

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lg

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pn

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Ore

feed

Red

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Leach

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ore

Perc

en

tag

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iin

ph

ase

N

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ph

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tag

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iin

ph

ase

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tal

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Lim

onite

com

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part

icle

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limonite

com

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part

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s1 1

Fe

rich

matr

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947 4

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152 8

0 2

68 2

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oeth

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(FeN

i)O

(OH

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ndashndash

ndashndash

1 3

m

ag

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eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

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1 7

94 3

2 7

00 5

0 7

70 7

1 8

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ine

(Mg

FeN

i)2S

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1 3

80 6

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95 9

0 8

92 5

1 8

a

oliv

inendashserp

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com

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1 8

a1

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1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

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s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

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eN

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2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

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ndashndash

ndashndash

0 4

11 2

1a8

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inendashserp

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com

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a1

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entine

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ndashndash

1 0

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ndashndash

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Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

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0 0

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0 0

50 1

0 0

50 2

Serp

entine

7

serp

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7

serp

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(Mg

FeN

i)3S

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5(O

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2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

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with

mag

netite

inclu

sio

ns

7a1

serp

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(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

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m

ag

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eN

i)O

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2O

30 3

30 0

ndashndash

ndashndash

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ine

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oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

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(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

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Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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ions

Ltd

reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

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There was a change in the particle size distribution ofthe ore samples upon reduction roasting as shown inFig 1 The distribution was shifted to the right themean particle size of the sample was increased from 21to 43 mm The volume percentage of particles with asize larger than 100 mm in ore was increased from 6 to13 vol- The changes in the distribution were mainlyassociated with the agglomeration of the materials uponreduction roasting

The mean particle size of the leached ore sample was35 mm smaller than that of reduced ore ie 43 mm Itcan also be seen from Fig 1 that the distribution isslightly shifted to the left The volume percentage ofparticles with a size 100 mm in the leached ore samplesis 57 vol-

Synchrotron X-ray powder diffraction analyses werecarried out on the ore feed reduced ore and leached oresamples to identify the crystalline phases present in thematerials The resultant SXRD spectra are shown inFig 2 It can be seen that in the case of ore feed samplethe major peaks present are identified to be from

goethite [(FeNi)O(OH)] serpentine-lizardite[(MgFeNi)3Si2O5(OH)4 quartz SiO2] and spinel Fe-chromite [(FeMg)O(Cr Al Fe)2O3] The peaksobserved in the reduced ore sample are of olivine[(MgFeNi)2SiO4] magnetite [(FeNi)OFe2O3] quartzspinel Fe chromite and taenite (FeNi) alloy The peaksobserved in the leached ore are similar as in the reducedore however the peaks of taenite do not appearconfirming the nickel dissolution upon leaching

Ore feed sampleTable 2 shows the summary of the average compositionsof the particles and phases observed in the ore feedsamples measured using EPMA The results arepresented in terms of oxides composition (mass-) andare average values of multiple measurements conductedon a number of similar particlesphases The composi-tions presented are normalised values It should be notedthat in the case of goethite (and fine grained matrix) andserpentine the total counts of the EPMA measurementare 100 due to the present of water of crystal-lisation For simplicity only particles with a proportion1 are reported Trace elements observed in eachphases such as Ca Mn Cu Ti Na K Zn Pb and Coare also not reported

The approximate proportions of the various particles(mass-) in the sample as well as the relative propor-tions (on average) of phases present in each observedparticle are also presented in Table 2 (in columns 2 and5 respectively) These compositions were approximatedby reconciling mass balance using the results of EPMAmeasurements SEM observations and chemical bulkanalysis (Table 1)

Figure 3a shows an example of an SEM image(backscattered electron image) of the ore feed sampleat low magnification showing the general microstruc-ture of the particles The greyscale in the image showsthe relative mean atomic number of the material thusrepresenting differences in compositions The numberson the images were assigned to represent a particularparticle type or phase according to Table 2 In generalcomplex structures such as composite intergrowthvein-likeplate-like porous and dense structures wereobserved in the particles in the ore feed sample

2 Synchrotron X-ray powder diffraction spectra (synchro-

tron radiation wavelength 08 A) of nickel laterite ore

feed reduced ore and leached ore samples [L lizardite

(serpentine) G goethite Q quartz Si silicon stan-

dard O olivine M magnetite S spinel (Fendashchromite)

T taenite (FendashNi alloy)]

1 limonite composite particle 3 magnetite 5 chromite 7 serpentine 9 quartz 11 Fe rich matrix 12 goethite 13magnetite 17 serpentine

3 Scanning electron microscope backscattered electron micrographs of ore feed samples showing a overview of micro-

structures of particles and b detailed microstructure of limonite composite particle (no 1 in a)

Rhamdhani et al Nickel laterite Part 1

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35 0

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(FeM

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17 7

0 0

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6 0

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22 6

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1 1

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ine

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1 0

0 6

40 7

46 5

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0 7

1 7

40 6

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a

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1 0

0 6

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39 5

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1 8

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1 0

0 6

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47 4

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22 0

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97 8

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Goeth

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ite

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ite

(FeN

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3100 0

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Serp

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24 0

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100 0

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7a

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ine

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100 0

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16 5

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1 6

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0 0

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50 0

0 5

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6 8

0 1

0 1

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50 0

0 5

40 6

49 8

6 8

0 4

0 7

1 6

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Quart

z3 0

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2100 0

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0 1

99 3

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0 0

20 0

0 0

0Tota

l100

100

1 4

9

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 133

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In the current discussion the ore particles wereclassified into two categories ie single phase andcomposite particles The single phase particle refers toa particle that consists of only a single phase (with orwithout small amount of inclusions) The compositeparticle in this case refers to agglomerated particles withvarious phases embedded in a matrix or a blend(intergrowth) between two or more phases or mineralgrains

It can be seen from Table 2 that the major phasesmixtures observed in the ore feed sample include Fe richmatrix (a fine grain mixture of goethite and silicateminerals) goethite and serpentine Other phasesobserved include quartz olivine magnetite and chro-mite Trace phases (not included in Table 2) observedinclude CandashMg silicate (diopside) forsterite nickeloan(NiO2MgO4SiO2) FendashMn silicate pyroxene[(MgCaFeNi)SiO3] and gibbsite [Al(OH)3] In thecurrent study general mineral species names werereported no attempts were made to distinguish theprecise mineral species

Limonite composite particles

The majority of the coarse particles 60 mass- of thetotal ore sample were limonite composite particles ieparticles consisting of fine grains of Fe rich mineralmatrix with inclusion phases embedded in it (labelledno 1 in Fig 3a) The limonite composite particles inaverage contain of 70 of Fe rich matrix and 30 ofother phasegrain inclusions Most of these limonitecomposite particles have sizes in the range of hundredsof micrometres The remainder of the coarse particleswere no 7 (serpentine 26 mass-) and other singlephase particles such as no 3 (magnetite) no 5 (chro-mite) and no 9 (quartz) as shown in Fig 3a Magnetiteand chromite phases appear bright in the backscatteredelectron images and others appear as darker grey phases

Figure 3b shows in more detail the limonite compositeparticle This particular composite consists of smallergrainsphases of no 12 (goethite) no 13 (magnetiteappear as bright phases) and no 17 (serpentine)embedded in no 11 (Fe rich matrix) The inclusionphasesgrains in the matrix have different types ofmorphology such as needle-like plate-like and roundshapes with a size ranging from 1 mm to tens ofmicrometres

The matrix of the limonite composite particlesconsists mainly of Fe and other elements such as SiMg and Al in lower concentrations Considering thelarge concentration of the matrix in the ore feedsamples and by reconciling with X-ray powder diffrac-tion analysis results it was concluded that this matrixmainly consists of a mixture of fine grained goethite withsilicate minerals ie serpentine

There were variations in composition in the fine grainmatrix between particles and within a particle Thenickel oxide concentration in the matrix was found tovary from about 005ndash to 620 mass- In the particle inFig 3b the average nickel oxide concentration in thematrix was 214 mass- For comparison the nickeloxide concentration of no 12 (goethite) inside thelimonite composite particles was 142 mass- onaverage It should be noted that no separate NiO orCoO particles were observed The clear indications fromthe analyses are that the Ni and Co are present in dilute

solid solution mostly in the goethite magnetite serpen-tine and olivine crystal lattice

Serpentine particles

Serpentine was present as a single phase (dense orporous) particles as well as composite particlesexamples of these microstructures are shown in Fig 4There were variations in composition between serpen-tine particles (in terms of MgFe ratio and mass-NiO)and within a particle in some of the serpentine iedemonstrated by two or more different grey regionsInclusions (such as magnetite) may also be present insidethese serpentine particles Figure 4a shows a singlephase large serpentine particle with dense morphology(a particle size of 500 mm) A single phase serpentineparticle with two different grey areas is shown in Fig 4bIn this particular particle the light grey area has a lowernickel oxide concentration compared to the darker area162 and 295 mass-NiO respectively The correspond-ing MgFe molar ratios in these areas are 79 and 70respectively Figure 4c and d shows other types ofserpentine microstructure ie a vein-like serpentine andan olivinendashserpentine composite In the case of vein-likestructure the particle consists of intertwined plate-likeand dense serpentine with porous serpentine in betweenThe different types of serpentine structure as well as thevariations in the compositions reflect the way thematerials formed during their weathering processes2324

Other single phase particles

Figure 5 shows examples of the microstructures ofvarious single phase particles found in the ore feedsamples Apart from the particles inside the limonitecomposite particles magnetite was also observed assingle phase particles as shown in Fig 5a Themicrostructure of the single phase particles was quitedifferent compared to magnetite inside the limonitecomposite particles They had a dense structure withsome pores and fissures this in contrast with the fineneedle-like structure observed inside the limonite com-posite particle Number 9 (quartz) was also present as aninclusion phase in the limonite composite particles andas large single phase particles as shown in Fig 5bSingle phase no 5 [chromite (spinel) particle] with densemicrostructure is shown in Fig 5c Number 5 [chromite(spinel)] has significant variations in Mg Fe and Alcompositions from one particle to another For examplethe MgO Fe2O3 and Al2O3 concentrations were foundto vary from 53 to 131 mass- 166 to 4418 mass-and 60 to 187 mass- respectively Trace proportionsof chromite particles with high concentration of Al2O3

(vary from 202 to 376 mass- with an average of274 mass-) were also observed in the sample notincluded in Table 2

Other nickel bearing minerals observed in the samplesinclude forsterite nickeloan and no 13a (FendashMn silicatecomposite) ie FendashMn silicate surrounded by MnO asshown in Fig 5d both of these phases were observed intrace concentrations and also not included in Table 2The nickel oxide concentration of the forsterite nick-eloan can be up to 280 mass- with an average of196 mass-NiO The FendashMn silicate contains a sig-nificant amount of nickel ie varying from 24 to97 mass- with an average of 71 mass-NiO Otherminerals observed in trace proportions include pyrox-ene CandashMg silicate (diopside) and gibbsite

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The major X-ray diffraction peaks in the ore feedsample are identified to be from goethite and serpentine(lizardite) as shown in Fig 2 This result supports theEPMA measurements and also shows that the majorphases present in the ore feed sample are goethite andserpentine This result combined with SEM observationand EPMA results also confirms that the fine grainno 11 (Fe rich matrix) contains mainly the goethitephase

Reduced ore sampleThe summary of the average compositions measuredusing EPMA of the major particles and phases observedin the reduced ore samples is shown in Table 3 Themajor phasesmixtures observed in the reduced oresample include Fe rich matrix (fine grain mixture ofmagnetite and silicate minerals) olivine and magnetiteOther phases observed in low quantities include quartzand chromite Minor (trace) phases observed (not shownin Table 3) include forsterite nickeloan pyroxeneserpentine CandashMg silicate FendashMgndashAl silicate gibbsiteAl rich olivine and Al rich chromite

Overview microstructures (backscattered electronimages) of the particles observed in the reduced oresample are shown in Fig 6a Similar to the ore feedsamples the majority of the coarse particles (60 ofthe total) observed in the reduced ore sample are no 1

(limonite composite particles) The bright particlesobserved in the reduced ore sample are no 3 (magne-tite) no 4 (magnetite with chromite inclusions) andno 5 (chromite) Number 8 (olivine) and no 9 (quartz)particles are also observed and appear as grey phases inthe image

Limonite composite particles

In general the composite particles in the reduced oresamples have similar characteristics to that observed inthe ore feed However more bright phases exhibiting aneedle like shape as well as porous structure withrounded shape of sizes ranging from 1 mm to tens ofmicrometres were observed in the Fe rich matrix as canbe seen in Fig 6 These bright phases correspond tomagnetite which appeared to be transformed fromgoethite upon reduction roasting

In an oxidising condition such as in air goethite istransformed to hematite (Fe2O3) upon roasting In areducing condition with very low oxygen partial pres-sure such as in the current study (pO2

~32|1015 Pa)the goethite appeared to transform to magnetite follow-ing reaction (1)

6(Fe Ni)OOH2(Fe Ni)3O4z3H2Oz1=2O2 (1)

The transformation of goethite to magnetite in thereduced ore is supported by the X-ray powder diffraction

a dense 75serpentine b 75serpentine with different Ni concentrations c 75vein-like structure d 8a5olivinendashserpentinecomposite

4 Scanning electron microscope backscattered electron micrographs showing details of different microstructures of ser-

pentine particles observed in ore feed samples

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

3S

um

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icle

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A

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part

icle

s

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pro

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mp

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ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

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icle

s

60 0

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix71 7

43 0

2 3

6 8

73 1

1 2

4 0

2 4

152 8

1 0

01 3

m

ag

netite

(F

eN

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Fe

2O

317 0

10 2

0 4

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91 0

2 4

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14 7

1 5

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(C

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1 0

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21 9

0 1

30 1

1 7

serp

entine

(Mg

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i 2O

5(O

H) 4

0 5

0 3

23 6

43 0

14 6

0 3

2 0

3 4

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1 8

oliv

ine

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0 1

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719 5

0 5

05 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

3 0

30 8

44 8

8 9

0 5

3 4

2 3

83 6

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

2 0

28 6

48 2

6 8

0 3

0 6

2 3

32 4

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

28 7

44 4

14 1

0 3

0 5

2 7

86 7

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

z9

quart

z

SiO

2100 0

4 5

0 3

98 2

1 1

0 0

0 1

0 0

70 2

0 0

0Tota

l100

100

1 5

4

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 137

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

Rhamdhani et al Nickel laterite Part 1

138 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 139

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

140 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

xim

ate

pro

po

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fto

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mass-

Part

icle

Ph

asem

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lg

rou

pn

am

e

Ap

pro

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ate

pro

po

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nin

part

icle

s

Ap

pro

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ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

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part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

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33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

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0 5

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1a8

a

oliv

inendashserp

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com

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34 1

1

serp

entine

0 5

0 2

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44 9

7 3

0 2

0 5

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0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

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5S

um

ma

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dis

trib

uti

on

inm

ajo

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nd

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ph

as

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on

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tue

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ea

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by

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ino

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re

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ce

do

rea

nd

lea

ch

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sa

mp

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Part

icle

Ph

asem

inera

lg

rou

pn

am

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Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

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iin

ph

ase

N

ito

talN

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tag

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ph

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P

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tag

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ph

ase

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tal

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Lim

onite

com

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part

icle

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limonite

com

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part

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s1 1

Fe

rich

matr

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947 4

1 9

152 8

0 2

68 2

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g

oeth

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(FeN

i)O

(OH

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25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

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1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

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com

posite

1a8

a1

serp

entine

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ndashndash

1 0

40 4

1a8

a2

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ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

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7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

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with

mag

netite

inclu

sio

ns

7a1

serp

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(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

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2O

30 3

30 0

ndashndash

ndashndash

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ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

2S

um

ma

ryo

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ajo

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icle

an

dp

ha

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av

era

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co

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os

itio

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ea

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by

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MA

o

bs

erv

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ino

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ed

sa

mp

le

Ap

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pro

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mass-

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icle

Ph

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icle

s

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of

tota

l

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OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

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nt

mass-

mass-

Lim

onite

com

posite

part

icle

60 0

1

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix70 0

42 0

3 8

7 6

70 2

1 4

4 4

2 1

447 4

0 8

91 2

g

oeth

ite

(FeN

i)O

(OH

)12 0

7 2

0 6

2 2

79 6

1 8

3 9

1 4

25 4

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

35 0

3 0

0 4

0 8

91 4

3 0

3 4

0 4

70 7

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

1 2

9 8

0 1

21 3

50 5

17 7

0 0

80 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

6 0

3 6

27 5

32 9

22 6

0 4

1 1

2 2

64 3

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 0

0 6

40 7

46 5

9 4

0 2

0 7

1 7

40 6

1 8

a

oliv

inendash

serp

entine

com

posite

1 8

a1

serp

entine

1 0

0 6

33 4

39 5

9 0

1 8

0 4

2 3

30 7

1 8

a2

oliv

ine

1 0

0 6

43 2

47 4

5 5

0 8

1 3

1 6

40 5

1 9

q

uart

z

SiO

22 0

1 2

0 2

97 8

1 6

0 0

0 1

0 0

70 0

Goeth

ite

5 0

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)100 0

5 0

1 2

1 9

78 8

1 7

4 7

1 0

32 7

0 0

4S

pin

el

2 0

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

1 5

0 3

0 8

90 9

3 5

3 6

0 3

40 3

0 0

12 0

5

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

9 1

0 1

26 1

50 8

13 3

0 0

90 1

Serp

entine

24 0

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

100 0

24 0

32 1

39 6

10 0

0 2

2 2

2 6

533 5

0 5

22 0

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

95 0

1 9

35 8

39 4

9 2

0 2

0 5

1 6

81 7

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

35 0

0 1

1 1

1 4

92 8

2 3

1 7

0 4

10 0

Oliv

ine

1 0

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

1 0

36 3

43 5

16 5

0 2

1 6

1 6

10 8

0 0

31 0

8a

oliv

inendash

serp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

50 0

0 5

34 3

42 9

6 8

0 1

0 1

2 6

50 7

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

50 0

0 5

40 6

49 8

6 8

0 4

0 7

1 6

40 4

Quart

z3 0

9

quart

z9

quart

z

SiO

2100 0

3 0

0 1

99 3

0 4

0 1

0 0

0 0

20 0

0 0

0Tota

l100

100

1 4

9

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 133

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In the current discussion the ore particles wereclassified into two categories ie single phase andcomposite particles The single phase particle refers toa particle that consists of only a single phase (with orwithout small amount of inclusions) The compositeparticle in this case refers to agglomerated particles withvarious phases embedded in a matrix or a blend(intergrowth) between two or more phases or mineralgrains

It can be seen from Table 2 that the major phasesmixtures observed in the ore feed sample include Fe richmatrix (a fine grain mixture of goethite and silicateminerals) goethite and serpentine Other phasesobserved include quartz olivine magnetite and chro-mite Trace phases (not included in Table 2) observedinclude CandashMg silicate (diopside) forsterite nickeloan(NiO2MgO4SiO2) FendashMn silicate pyroxene[(MgCaFeNi)SiO3] and gibbsite [Al(OH)3] In thecurrent study general mineral species names werereported no attempts were made to distinguish theprecise mineral species

Limonite composite particles

The majority of the coarse particles 60 mass- of thetotal ore sample were limonite composite particles ieparticles consisting of fine grains of Fe rich mineralmatrix with inclusion phases embedded in it (labelledno 1 in Fig 3a) The limonite composite particles inaverage contain of 70 of Fe rich matrix and 30 ofother phasegrain inclusions Most of these limonitecomposite particles have sizes in the range of hundredsof micrometres The remainder of the coarse particleswere no 7 (serpentine 26 mass-) and other singlephase particles such as no 3 (magnetite) no 5 (chro-mite) and no 9 (quartz) as shown in Fig 3a Magnetiteand chromite phases appear bright in the backscatteredelectron images and others appear as darker grey phases

Figure 3b shows in more detail the limonite compositeparticle This particular composite consists of smallergrainsphases of no 12 (goethite) no 13 (magnetiteappear as bright phases) and no 17 (serpentine)embedded in no 11 (Fe rich matrix) The inclusionphasesgrains in the matrix have different types ofmorphology such as needle-like plate-like and roundshapes with a size ranging from 1 mm to tens ofmicrometres

The matrix of the limonite composite particlesconsists mainly of Fe and other elements such as SiMg and Al in lower concentrations Considering thelarge concentration of the matrix in the ore feedsamples and by reconciling with X-ray powder diffrac-tion analysis results it was concluded that this matrixmainly consists of a mixture of fine grained goethite withsilicate minerals ie serpentine

There were variations in composition in the fine grainmatrix between particles and within a particle Thenickel oxide concentration in the matrix was found tovary from about 005ndash to 620 mass- In the particle inFig 3b the average nickel oxide concentration in thematrix was 214 mass- For comparison the nickeloxide concentration of no 12 (goethite) inside thelimonite composite particles was 142 mass- onaverage It should be noted that no separate NiO orCoO particles were observed The clear indications fromthe analyses are that the Ni and Co are present in dilute

solid solution mostly in the goethite magnetite serpen-tine and olivine crystal lattice

Serpentine particles

Serpentine was present as a single phase (dense orporous) particles as well as composite particlesexamples of these microstructures are shown in Fig 4There were variations in composition between serpen-tine particles (in terms of MgFe ratio and mass-NiO)and within a particle in some of the serpentine iedemonstrated by two or more different grey regionsInclusions (such as magnetite) may also be present insidethese serpentine particles Figure 4a shows a singlephase large serpentine particle with dense morphology(a particle size of 500 mm) A single phase serpentineparticle with two different grey areas is shown in Fig 4bIn this particular particle the light grey area has a lowernickel oxide concentration compared to the darker area162 and 295 mass-NiO respectively The correspond-ing MgFe molar ratios in these areas are 79 and 70respectively Figure 4c and d shows other types ofserpentine microstructure ie a vein-like serpentine andan olivinendashserpentine composite In the case of vein-likestructure the particle consists of intertwined plate-likeand dense serpentine with porous serpentine in betweenThe different types of serpentine structure as well as thevariations in the compositions reflect the way thematerials formed during their weathering processes2324

Other single phase particles

Figure 5 shows examples of the microstructures ofvarious single phase particles found in the ore feedsamples Apart from the particles inside the limonitecomposite particles magnetite was also observed assingle phase particles as shown in Fig 5a Themicrostructure of the single phase particles was quitedifferent compared to magnetite inside the limonitecomposite particles They had a dense structure withsome pores and fissures this in contrast with the fineneedle-like structure observed inside the limonite com-posite particle Number 9 (quartz) was also present as aninclusion phase in the limonite composite particles andas large single phase particles as shown in Fig 5bSingle phase no 5 [chromite (spinel) particle] with densemicrostructure is shown in Fig 5c Number 5 [chromite(spinel)] has significant variations in Mg Fe and Alcompositions from one particle to another For examplethe MgO Fe2O3 and Al2O3 concentrations were foundto vary from 53 to 131 mass- 166 to 4418 mass-and 60 to 187 mass- respectively Trace proportionsof chromite particles with high concentration of Al2O3

(vary from 202 to 376 mass- with an average of274 mass-) were also observed in the sample notincluded in Table 2

Other nickel bearing minerals observed in the samplesinclude forsterite nickeloan and no 13a (FendashMn silicatecomposite) ie FendashMn silicate surrounded by MnO asshown in Fig 5d both of these phases were observed intrace concentrations and also not included in Table 2The nickel oxide concentration of the forsterite nick-eloan can be up to 280 mass- with an average of196 mass-NiO The FendashMn silicate contains a sig-nificant amount of nickel ie varying from 24 to97 mass- with an average of 71 mass-NiO Otherminerals observed in trace proportions include pyrox-ene CandashMg silicate (diopside) and gibbsite

Rhamdhani et al Nickel laterite Part 1

134 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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The major X-ray diffraction peaks in the ore feedsample are identified to be from goethite and serpentine(lizardite) as shown in Fig 2 This result supports theEPMA measurements and also shows that the majorphases present in the ore feed sample are goethite andserpentine This result combined with SEM observationand EPMA results also confirms that the fine grainno 11 (Fe rich matrix) contains mainly the goethitephase

Reduced ore sampleThe summary of the average compositions measuredusing EPMA of the major particles and phases observedin the reduced ore samples is shown in Table 3 Themajor phasesmixtures observed in the reduced oresample include Fe rich matrix (fine grain mixture ofmagnetite and silicate minerals) olivine and magnetiteOther phases observed in low quantities include quartzand chromite Minor (trace) phases observed (not shownin Table 3) include forsterite nickeloan pyroxeneserpentine CandashMg silicate FendashMgndashAl silicate gibbsiteAl rich olivine and Al rich chromite

Overview microstructures (backscattered electronimages) of the particles observed in the reduced oresample are shown in Fig 6a Similar to the ore feedsamples the majority of the coarse particles (60 ofthe total) observed in the reduced ore sample are no 1

(limonite composite particles) The bright particlesobserved in the reduced ore sample are no 3 (magne-tite) no 4 (magnetite with chromite inclusions) andno 5 (chromite) Number 8 (olivine) and no 9 (quartz)particles are also observed and appear as grey phases inthe image

Limonite composite particles

In general the composite particles in the reduced oresamples have similar characteristics to that observed inthe ore feed However more bright phases exhibiting aneedle like shape as well as porous structure withrounded shape of sizes ranging from 1 mm to tens ofmicrometres were observed in the Fe rich matrix as canbe seen in Fig 6 These bright phases correspond tomagnetite which appeared to be transformed fromgoethite upon reduction roasting

In an oxidising condition such as in air goethite istransformed to hematite (Fe2O3) upon roasting In areducing condition with very low oxygen partial pres-sure such as in the current study (pO2

~32|1015 Pa)the goethite appeared to transform to magnetite follow-ing reaction (1)

6(Fe Ni)OOH2(Fe Ni)3O4z3H2Oz1=2O2 (1)

The transformation of goethite to magnetite in thereduced ore is supported by the X-ray powder diffraction

a dense 75serpentine b 75serpentine with different Ni concentrations c 75vein-like structure d 8a5olivinendashserpentinecomposite

4 Scanning electron microscope backscattered electron micrographs showing details of different microstructures of ser-

pentine particles observed in ore feed samples

Rhamdhani et al Nickel laterite Part 1

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

3S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inre

du

ce

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

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pro

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Part

icle

Ph

asem

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lg

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pn

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Ap

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ate

pro

po

rtio

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part

icle

s

Ap

pro

xim

ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

60 0

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix71 7

43 0

2 3

6 8

73 1

1 2

4 0

2 4

152 8

1 0

01 3

m

ag

netite

(F

eN

i)O

Fe

2O

317 0

10 2

0 4

1 5

91 0

2 4

3 5

0 9

14 7

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 7

1 0

10 7

0 6

22 4

44 0

21 9

0 1

30 1

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

0 5

0 3

23 6

43 0

14 6

0 3

2 0

3 4

20 5

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 3

3 8

39 3

46 7

9 8

0 1

1 0

3 0

35 9

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

0 3

0 2

31 1

45 1

5 6

0 4

3 5

1 1

30 1

1 8

a2

oliv

ine

0 7

0 4

41 6

44 3

9 6

0 2

2 2

1 9

70 4

1 8

b

oliv

ine

with

Mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

0 9

0 5

18 0

44 5

32 2

0 4

2 0

2 6

80 7

1 8

b2

m

ag

netite

0 1

0 1

0 1

0 5

89 7

4 5

4 6

0 1

00 0

1 9

q

uart

z

SiO

20 8

0 5

0 1

99 0

0 8

0 0

0 0

0 0

50 0

Sp

inel

4 5

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

4 5

0 5

1 2

92 6

2 0

2 9

0 6

21 4

0 0

20 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 6

1 2

86 5

2 3

2 8

0 5

80 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

9 7

0 2

23 0

54 8

11 8

0 0

40 0

1 5

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

1 5

9 1

0 7

23 9

53 1

12 7

0 0

70 1

Oliv

ine

18 5

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

18 5

38 8

46 9

11 7

0 1

0 4

2 0

719 5

0 5

05 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

3 0

30 8

44 8

8 9

0 5

3 4

2 3

83 6

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

2 0

28 6

48 2

6 8

0 3

0 6

2 3

32 4

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

28 7

44 4

14 1

0 3

0 5

2 7

86 7

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

z9

quart

z

SiO

2100 0

4 5

0 3

98 2

1 1

0 0

0 1

0 0

70 2

0 0

0Tota

l100

100

1 5

4

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Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 137

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

Rhamdhani et al Nickel laterite Part 1

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

Rhamdhani et al Nickel laterite Part 1

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

xim

ate

pro

po

rtio

no

fto

tal

mass-

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ap

pro

xim

ate

pro

po

rtio

nin

part

icle

s

Ap

pro

xim

ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

posite

33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

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Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

eir

ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

ed

ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

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In the current discussion the ore particles wereclassified into two categories ie single phase andcomposite particles The single phase particle refers toa particle that consists of only a single phase (with orwithout small amount of inclusions) The compositeparticle in this case refers to agglomerated particles withvarious phases embedded in a matrix or a blend(intergrowth) between two or more phases or mineralgrains

It can be seen from Table 2 that the major phasesmixtures observed in the ore feed sample include Fe richmatrix (a fine grain mixture of goethite and silicateminerals) goethite and serpentine Other phasesobserved include quartz olivine magnetite and chro-mite Trace phases (not included in Table 2) observedinclude CandashMg silicate (diopside) forsterite nickeloan(NiO2MgO4SiO2) FendashMn silicate pyroxene[(MgCaFeNi)SiO3] and gibbsite [Al(OH)3] In thecurrent study general mineral species names werereported no attempts were made to distinguish theprecise mineral species

Limonite composite particles

The majority of the coarse particles 60 mass- of thetotal ore sample were limonite composite particles ieparticles consisting of fine grains of Fe rich mineralmatrix with inclusion phases embedded in it (labelledno 1 in Fig 3a) The limonite composite particles inaverage contain of 70 of Fe rich matrix and 30 ofother phasegrain inclusions Most of these limonitecomposite particles have sizes in the range of hundredsof micrometres The remainder of the coarse particleswere no 7 (serpentine 26 mass-) and other singlephase particles such as no 3 (magnetite) no 5 (chro-mite) and no 9 (quartz) as shown in Fig 3a Magnetiteand chromite phases appear bright in the backscatteredelectron images and others appear as darker grey phases

Figure 3b shows in more detail the limonite compositeparticle This particular composite consists of smallergrainsphases of no 12 (goethite) no 13 (magnetiteappear as bright phases) and no 17 (serpentine)embedded in no 11 (Fe rich matrix) The inclusionphasesgrains in the matrix have different types ofmorphology such as needle-like plate-like and roundshapes with a size ranging from 1 mm to tens ofmicrometres

The matrix of the limonite composite particlesconsists mainly of Fe and other elements such as SiMg and Al in lower concentrations Considering thelarge concentration of the matrix in the ore feedsamples and by reconciling with X-ray powder diffrac-tion analysis results it was concluded that this matrixmainly consists of a mixture of fine grained goethite withsilicate minerals ie serpentine

There were variations in composition in the fine grainmatrix between particles and within a particle Thenickel oxide concentration in the matrix was found tovary from about 005ndash to 620 mass- In the particle inFig 3b the average nickel oxide concentration in thematrix was 214 mass- For comparison the nickeloxide concentration of no 12 (goethite) inside thelimonite composite particles was 142 mass- onaverage It should be noted that no separate NiO orCoO particles were observed The clear indications fromthe analyses are that the Ni and Co are present in dilute

solid solution mostly in the goethite magnetite serpen-tine and olivine crystal lattice

Serpentine particles

Serpentine was present as a single phase (dense orporous) particles as well as composite particlesexamples of these microstructures are shown in Fig 4There were variations in composition between serpen-tine particles (in terms of MgFe ratio and mass-NiO)and within a particle in some of the serpentine iedemonstrated by two or more different grey regionsInclusions (such as magnetite) may also be present insidethese serpentine particles Figure 4a shows a singlephase large serpentine particle with dense morphology(a particle size of 500 mm) A single phase serpentineparticle with two different grey areas is shown in Fig 4bIn this particular particle the light grey area has a lowernickel oxide concentration compared to the darker area162 and 295 mass-NiO respectively The correspond-ing MgFe molar ratios in these areas are 79 and 70respectively Figure 4c and d shows other types ofserpentine microstructure ie a vein-like serpentine andan olivinendashserpentine composite In the case of vein-likestructure the particle consists of intertwined plate-likeand dense serpentine with porous serpentine in betweenThe different types of serpentine structure as well as thevariations in the compositions reflect the way thematerials formed during their weathering processes2324

Other single phase particles

Figure 5 shows examples of the microstructures ofvarious single phase particles found in the ore feedsamples Apart from the particles inside the limonitecomposite particles magnetite was also observed assingle phase particles as shown in Fig 5a Themicrostructure of the single phase particles was quitedifferent compared to magnetite inside the limonitecomposite particles They had a dense structure withsome pores and fissures this in contrast with the fineneedle-like structure observed inside the limonite com-posite particle Number 9 (quartz) was also present as aninclusion phase in the limonite composite particles andas large single phase particles as shown in Fig 5bSingle phase no 5 [chromite (spinel) particle] with densemicrostructure is shown in Fig 5c Number 5 [chromite(spinel)] has significant variations in Mg Fe and Alcompositions from one particle to another For examplethe MgO Fe2O3 and Al2O3 concentrations were foundto vary from 53 to 131 mass- 166 to 4418 mass-and 60 to 187 mass- respectively Trace proportionsof chromite particles with high concentration of Al2O3

(vary from 202 to 376 mass- with an average of274 mass-) were also observed in the sample notincluded in Table 2

Other nickel bearing minerals observed in the samplesinclude forsterite nickeloan and no 13a (FendashMn silicatecomposite) ie FendashMn silicate surrounded by MnO asshown in Fig 5d both of these phases were observed intrace concentrations and also not included in Table 2The nickel oxide concentration of the forsterite nick-eloan can be up to 280 mass- with an average of196 mass-NiO The FendashMn silicate contains a sig-nificant amount of nickel ie varying from 24 to97 mass- with an average of 71 mass-NiO Otherminerals observed in trace proportions include pyrox-ene CandashMg silicate (diopside) and gibbsite

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The major X-ray diffraction peaks in the ore feedsample are identified to be from goethite and serpentine(lizardite) as shown in Fig 2 This result supports theEPMA measurements and also shows that the majorphases present in the ore feed sample are goethite andserpentine This result combined with SEM observationand EPMA results also confirms that the fine grainno 11 (Fe rich matrix) contains mainly the goethitephase

Reduced ore sampleThe summary of the average compositions measuredusing EPMA of the major particles and phases observedin the reduced ore samples is shown in Table 3 Themajor phasesmixtures observed in the reduced oresample include Fe rich matrix (fine grain mixture ofmagnetite and silicate minerals) olivine and magnetiteOther phases observed in low quantities include quartzand chromite Minor (trace) phases observed (not shownin Table 3) include forsterite nickeloan pyroxeneserpentine CandashMg silicate FendashMgndashAl silicate gibbsiteAl rich olivine and Al rich chromite

Overview microstructures (backscattered electronimages) of the particles observed in the reduced oresample are shown in Fig 6a Similar to the ore feedsamples the majority of the coarse particles (60 ofthe total) observed in the reduced ore sample are no 1

(limonite composite particles) The bright particlesobserved in the reduced ore sample are no 3 (magne-tite) no 4 (magnetite with chromite inclusions) andno 5 (chromite) Number 8 (olivine) and no 9 (quartz)particles are also observed and appear as grey phases inthe image

Limonite composite particles

In general the composite particles in the reduced oresamples have similar characteristics to that observed inthe ore feed However more bright phases exhibiting aneedle like shape as well as porous structure withrounded shape of sizes ranging from 1 mm to tens ofmicrometres were observed in the Fe rich matrix as canbe seen in Fig 6 These bright phases correspond tomagnetite which appeared to be transformed fromgoethite upon reduction roasting

In an oxidising condition such as in air goethite istransformed to hematite (Fe2O3) upon roasting In areducing condition with very low oxygen partial pres-sure such as in the current study (pO2

~32|1015 Pa)the goethite appeared to transform to magnetite follow-ing reaction (1)

6(Fe Ni)OOH2(Fe Ni)3O4z3H2Oz1=2O2 (1)

The transformation of goethite to magnetite in thereduced ore is supported by the X-ray powder diffraction

a dense 75serpentine b 75serpentine with different Ni concentrations c 75vein-like structure d 8a5olivinendashserpentinecomposite

4 Scanning electron microscope backscattered electron micrographs showing details of different microstructures of ser-

pentine particles observed in ore feed samples

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

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icle

s

1 1

Fe

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matr

ix71 7

43 0

2 3

6 8

73 1

1 2

4 0

2 4

152 8

1 0

01 3

m

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317 0

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1 7

1 0

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0 1

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0 5

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23 6

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ine

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a

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1 8

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0 3

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5 6

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30 1

1 8

a2

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ine

0 7

0 4

41 6

44 3

9 6

0 2

2 2

1 9

70 4

1 8

b

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ine

with

Mag

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inclu

sio

ns

1 8

b1

oliv

ine

0 9

0 5

18 0

44 5

32 2

0 4

2 0

2 6

80 7

1 8

b2

m

ag

netite

0 1

0 1

0 1

0 5

89 7

4 5

4 6

0 1

00 0

1 9

q

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20 8

0 5

0 1

99 0

0 8

0 0

0 0

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Sp

inel

4 5

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mag

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mag

netite

(F

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3100 0

4 5

0 5

1 2

92 6

2 0

2 9

0 6

21 4

0 0

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04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

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Fe

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395 0

0 5

0 6

1 2

86 5

2 3

2 8

0 5

80 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

9 7

0 2

23 0

54 8

11 8

0 0

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1 5

05

chro

mite

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chro

mite

(FeM

g)O

(C

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9 1

0 7

23 9

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0 0

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ine

18 5

08

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ine

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ine

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FeN

i)2S

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100 0

18 5

38 8

46 9

11 7

0 1

0 4

2 0

719 5

0 5

05 0

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oliv

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entine

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oliv

ine

(Mg

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iO4

60 0

3 0

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44 8

8 9

0 5

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2 3

83 6

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

2 0

28 6

48 2

6 8

0 3

0 6

2 3

32 4

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

28 7

44 4

14 1

0 3

0 5

2 7

86 7

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

z9

quart

z

SiO

2100 0

4 5

0 3

98 2

1 1

0 0

0 1

0 0

70 2

0 0

0Tota

l100

100

1 5

4

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

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pro

xim

ate

pro

po

rtio

no

fto

tal

mass-

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ap

pro

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ate

pro

po

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nin

part

icle

s

Ap

pro

xim

ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

posite

33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

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ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

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0 0

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1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

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11 1

0 3

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1a8

a

oliv

inendashserp

entine

com

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34 1

1

serp

entine

0 5

0 2

34 2

44 9

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2

oliv

ine

0 5

0 2

42 0

47 9

7 0

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0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

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0 0

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30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

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48 9

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0 0

40 0

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chro

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5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

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11 1

0 0

22 4

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15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

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art

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nd

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on

sti

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ea

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red

by

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MA

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ino

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ed

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du

ce

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nd

lea

ch

ed

ore

sa

mp

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Part

icle

Ph

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lg

rou

pn

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e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

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iin

ph

ase

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ito

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P

erc

en

tag

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fN

iin

ph

ase

N

ito

tal

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Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

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rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

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eN

i)O

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2O

3ndash

ndashndash

ndash0 0

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1a7

serp

entine

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i)3S

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5(O

H) 4

ndashndash

ndashndash

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11 8

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ine

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FeN

i)2S

iO4

ndashndash

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inendashserp

entine

com

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entine

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ndashndash

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ine

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Goeth

ite

2

goeth

ite

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goeth

ite

(FeN

i)O

(OH

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12 7

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Sp

inel

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mag

netite

3

mag

netite

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i)O

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2O

30 2

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0 4

91 4

0 0

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4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

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2O

30 1

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5

CH

RO

MIT

E5

chro

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g)O

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0 0

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Serp

entine

7

serp

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7

serp

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i)3S

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933 5

2 1

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0 9

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7a

serp

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with

mag

netite

inclu

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7a1

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i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

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2O

30 3

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ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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The major X-ray diffraction peaks in the ore feedsample are identified to be from goethite and serpentine(lizardite) as shown in Fig 2 This result supports theEPMA measurements and also shows that the majorphases present in the ore feed sample are goethite andserpentine This result combined with SEM observationand EPMA results also confirms that the fine grainno 11 (Fe rich matrix) contains mainly the goethitephase

Reduced ore sampleThe summary of the average compositions measuredusing EPMA of the major particles and phases observedin the reduced ore samples is shown in Table 3 Themajor phasesmixtures observed in the reduced oresample include Fe rich matrix (fine grain mixture ofmagnetite and silicate minerals) olivine and magnetiteOther phases observed in low quantities include quartzand chromite Minor (trace) phases observed (not shownin Table 3) include forsterite nickeloan pyroxeneserpentine CandashMg silicate FendashMgndashAl silicate gibbsiteAl rich olivine and Al rich chromite

Overview microstructures (backscattered electronimages) of the particles observed in the reduced oresample are shown in Fig 6a Similar to the ore feedsamples the majority of the coarse particles (60 ofthe total) observed in the reduced ore sample are no 1

(limonite composite particles) The bright particlesobserved in the reduced ore sample are no 3 (magne-tite) no 4 (magnetite with chromite inclusions) andno 5 (chromite) Number 8 (olivine) and no 9 (quartz)particles are also observed and appear as grey phases inthe image

Limonite composite particles

In general the composite particles in the reduced oresamples have similar characteristics to that observed inthe ore feed However more bright phases exhibiting aneedle like shape as well as porous structure withrounded shape of sizes ranging from 1 mm to tens ofmicrometres were observed in the Fe rich matrix as canbe seen in Fig 6 These bright phases correspond tomagnetite which appeared to be transformed fromgoethite upon reduction roasting

In an oxidising condition such as in air goethite istransformed to hematite (Fe2O3) upon roasting In areducing condition with very low oxygen partial pres-sure such as in the current study (pO2

~32|1015 Pa)the goethite appeared to transform to magnetite follow-ing reaction (1)

6(Fe Ni)OOH2(Fe Ni)3O4z3H2Oz1=2O2 (1)

The transformation of goethite to magnetite in thereduced ore is supported by the X-ray powder diffraction

a dense 75serpentine b 75serpentine with different Ni concentrations c 75vein-like structure d 8a5olivinendashserpentinecomposite

4 Scanning electron microscope backscattered electron micrographs showing details of different microstructures of ser-

pentine particles observed in ore feed samples

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 135

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

Rhamdhani et al Nickel laterite Part 1

136 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

3S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inre

du

ce

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

xim

ate

pro

po

rtio

no

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tal

mass-

Part

icle

Ph

asem

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lg

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pn

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e

Ap

pro

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po

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icle

s

Ap

pro

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ate

co

mp

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ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

60 0

01

limonite

com

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part

icle

s

1 1

Fe

rich

matr

ix71 7

43 0

2 3

6 8

73 1

1 2

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2 4

152 8

1 0

01 3

m

ag

netite

(F

eN

i)O

Fe

2O

317 0

10 2

0 4

1 5

91 0

2 4

3 5

0 9

14 7

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 7

1 0

10 7

0 6

22 4

44 0

21 9

0 1

30 1

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

0 5

0 3

23 6

43 0

14 6

0 3

2 0

3 4

20 5

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 3

3 8

39 3

46 7

9 8

0 1

1 0

3 0

35 9

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

0 3

0 2

31 1

45 1

5 6

0 4

3 5

1 1

30 1

1 8

a2

oliv

ine

0 7

0 4

41 6

44 3

9 6

0 2

2 2

1 9

70 4

1 8

b

oliv

ine

with

Mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

0 9

0 5

18 0

44 5

32 2

0 4

2 0

2 6

80 7

1 8

b2

m

ag

netite

0 1

0 1

0 1

0 5

89 7

4 5

4 6

0 1

00 0

1 9

q

uart

z

SiO

20 8

0 5

0 1

99 0

0 8

0 0

0 0

0 0

50 0

Sp

inel

4 5

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

4 5

0 5

1 2

92 6

2 0

2 9

0 6

21 4

0 0

20 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 6

1 2

86 5

2 3

2 8

0 5

80 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

9 7

0 2

23 0

54 8

11 8

0 0

40 0

1 5

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

1 5

9 1

0 7

23 9

53 1

12 7

0 0

70 1

Oliv

ine

18 5

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

18 5

38 8

46 9

11 7

0 1

0 4

2 0

719 5

0 5

05 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

3 0

30 8

44 8

8 9

0 5

3 4

2 3

83 6

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

2 0

28 6

48 2

6 8

0 3

0 6

2 3

32 4

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

28 7

44 4

14 1

0 3

0 5

2 7

86 7

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

z9

quart

z

SiO

2100 0

4 5

0 3

98 2

1 1

0 0

0 1

0 0

70 2

0 0

0Tota

l100

100

1 5

4

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 137

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

Rhamdhani et al Nickel laterite Part 1

138 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 139

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

140 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

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os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

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PM

A

Ap

pro

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ate

pro

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mass-

Part

icle

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e

Ap

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part

icle

s

Ap

pro

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ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

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part

icle

s

22 5

01

limonite

com

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part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

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33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

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ph

as

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by

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do

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nd

lea

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sa

mp

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Part

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Ph

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lg

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pn

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Ore

feed

Red

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ore

Leach

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ore

Perc

en

tag

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iin

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ase

N

ito

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ph

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tal

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onite

com

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part

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com

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part

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s1 1

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matr

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947 4

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152 8

0 2

68 2

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(FeN

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(OH

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ndashndash

ndashndash

1 3

m

ag

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(F

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i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

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1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

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with

mag

netite

inclu

sio

ns

1 8

b1

oliv

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ndashndash

2 1

20 7

0 2

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Ag

glo

mera

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1a

ag

glo

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tes

of

sm

all

part

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rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

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entine

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ndashndash

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a2

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ine

ndashndash

ndashndash

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20 5

Goeth

ite

2

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ite

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goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

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Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

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(FeM

g)O

(C

rA

lFe) 2

O3

0 0

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0 0

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0 0

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Serp

entine

7

serp

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(Mg

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2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

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7a1

serp

entine

(Mg

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31 7

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ndashndash

Oliv

ine

8

oliv

ine

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oliv

ine

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1 2

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1 6

419 5

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8a

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inendashserp

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i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

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8a2

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ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

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ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

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results shown in Fig 2 Considering the large quantityof the matrix in the reduced ore sample and byreconciling with the XRD results and SEM images itwas concluded that the matrix is a mixture of fine grainmagnetite (transformed from goethite upon reductionroasting as per reaction (1)) with some silicate minerals

Upon reduction roasting the goethite in some smallerlimonite composite particles was transformed to a

porous magnetite particle interspersed with remainingFe silicate as can be seen in Fig 7a and b The evolvedmagnetite is quite different in terms of structure andcomposition compared to the original magnetite thatalready present in the ore feed samples for examplemagnetite shown in Fig 4a It has a porous structureas opposed to dense structure and in terms ofcomposition it has slightly higher silica and nickel

a 35magnetite particle b 95quartz particle composite c 55chromite particle d 13a5FendashMn silicate5 Scanning electron microscope backscattered electron micrographs showing detail microstructures of particles found

in ore feed samples (other phases inclusing 7 serpentine 13a1 FendashMn silicate 13a2 MnO)

1 limonite composite particle 11 Fe rich matrix 13 magnetite 18 olivine 3 magnetite 8 olivine6 Scanning electron microscope backscattered electron micrographs showing a general overview of microstructures of

reduced ore samples and b detailed microstructure of limonite composite particle (no 1 in a) from reduced ore sam-

ples showing formation of magnetite

Rhamdhani et al Nickel laterite Part 1

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Ta

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matr

ix71 7

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317 0

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chro

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g)O

(C

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O3

1 7

1 0

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0 6

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0 1

30 1

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

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0 5

0 3

23 6

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0 3

2 0

3 4

20 5

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 3

3 8

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0 1

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inendashserp

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with

Mag

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inclu

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0 1

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uart

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0 5

0 1

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inel

4 5

03

mag

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netite

(F

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3100 0

4 5

0 5

1 2

92 6

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0 6

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g)O

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g)O

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i)2S

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83 6

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

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H) 4

40 0

2 0

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6 8

0 3

0 6

2 3

32 4

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

28 7

44 4

14 1

0 3

0 5

2 7

86 7

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

z9

quart

z

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2100 0

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0 3

98 2

1 1

0 0

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0 0

0Tota

l100

100

1 5

4

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

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rich

matr

ix67 0

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1 9

5 1

75 9

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4 2

0 3

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318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

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2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

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(Mg

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i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

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com

posite

33 4

1

serp

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0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

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33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

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ine

with

mag

netite

inclu

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ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

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Ltd

matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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(c)

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Ltd

Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

eir

ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

ed

ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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ublis

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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ey P

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Com

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Ltd

Ta

ble

3S

um

ma

ryo

fm

ajo

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icle

an

dp

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ns

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ure

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Ap

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ion

of

tota

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Mg

OS

iO2

Fe

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Ni

tota

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i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

60 0

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix71 7

43 0

2 3

6 8

73 1

1 2

4 0

2 4

152 8

1 0

01 3

m

ag

netite

(F

eN

i)O

Fe

2O

317 0

10 2

0 4

1 5

91 0

2 4

3 5

0 9

14 7

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 7

1 0

10 7

0 6

22 4

44 0

21 9

0 1

30 1

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

0 5

0 3

23 6

43 0

14 6

0 3

2 0

3 4

20 5

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 3

3 8

39 3

46 7

9 8

0 1

1 0

3 0

35 9

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

0 3

0 2

31 1

45 1

5 6

0 4

3 5

1 1

30 1

1 8

a2

oliv

ine

0 7

0 4

41 6

44 3

9 6

0 2

2 2

1 9

70 4

1 8

b

oliv

ine

with

Mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

0 9

0 5

18 0

44 5

32 2

0 4

2 0

2 6

80 7

1 8

b2

m

ag

netite

0 1

0 1

0 1

0 5

89 7

4 5

4 6

0 1

00 0

1 9

q

uart

z

SiO

20 8

0 5

0 1

99 0

0 8

0 0

0 0

0 0

50 0

Sp

inel

4 5

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

4 5

0 5

1 2

92 6

2 0

2 9

0 6

21 4

0 0

20 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 6

1 2

86 5

2 3

2 8

0 5

80 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

9 7

0 2

23 0

54 8

11 8

0 0

40 0

1 5

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

1 5

9 1

0 7

23 9

53 1

12 7

0 0

70 1

Oliv

ine

18 5

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

18 5

38 8

46 9

11 7

0 1

0 4

2 0

719 5

0 5

05 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

3 0

30 8

44 8

8 9

0 5

3 4

2 3

83 6

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

2 0

28 6

48 2

6 8

0 3

0 6

2 3

32 4

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

28 7

44 4

14 1

0 3

0 5

2 7

86 7

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 1

0 9

89 3

4 2

4 7

0 3

40 0

Quart

z4 5

09

quart

z9

quart

z

SiO

2100 0

4 5

0 3

98 2

1 1

0 0

0 1

0 0

70 2

0 0

0Tota

l100

100

1 5

4

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 137

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

Rhamdhani et al Nickel laterite Part 1

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

Rhamdhani et al Nickel laterite Part 1

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

xim

ate

pro

po

rtio

no

fto

tal

mass-

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ap

pro

xim

ate

pro

po

rtio

nin

part

icle

s

Ap

pro

xim

ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

posite

33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

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Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

eir

ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

ed

ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

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Ltd oxide concentrations The original single phase dense

magnetite in the ore feed sample did not undergo anytransformation or other microstructure changes uponreduction roasting An example of this type of magnetiteis also shown in Fig 7a (particle at the bottom)

FendashNi alloy

It is expected that upon reduction roasting some FendashNialloy will form as has been reported by previousworkers1213 X-ray powder diffraction results of thereduced ore shown in Fig 2 suggest the presence of FendashNi alloy taenite in the reduced ore sample Howeverfrom the SEM observation of the cross-section of thegrains it was difficult to distinguish the metal alloy fromthe oxides (especially in the magnetite phase) from thebackscattered electron images as magnetite (and chro-mite) phase also give quite bright images relative to theother oxides and silicates in the vicinity

Numerous bright particles observed both inside andon the surrounding of the limonite composite andolivine particles in the reduced are vary in size fromsubmicrometre to hundreds of micrometres Uponanalysis using EPMA all of the bright particles withsizes 1 mm appear to be either magnetite or chromite

The EPMA quantitative analysis of the particles withsubmicrometre sizes (for example particles on thesurface of magnetite particle such as in Fig 7b) wasinconclusive as it requires a flat surface of particle withboth lateral and depth size of at least 1ndash2 mm Analysisof this particle will give erroneous and misleadingcomposition value since the surrounding matrix isincluded in the takeoff volume

Since it is expected that at least some of theferronickel alloy would be formed at the surface of theNi bearing particles the surface of the magnetite particlein the reduced ore sample was also examined usingSEM Figure 8a shows a high resolution secondaryelectron image at 6200 000 magnification of the surfaceof magnetite while Fig 8b shows a backscatteredelectron image at lower magnification Observationsusing SEM revealed many bright nanosize particles onthe surfaces of the selected magnetite particles Based onthe electron imaging conditions used it was anticipatedthat these are the ferronickel alloy nuclei produced as aresult of the reduction roasting It can be seen fromFig 8a that the size of the metal nuclei is about 15ndash20 nm in diameter These are the first direct observa-tions of FendashNi alloy particles formed interspersed with

a 15limonite composite particle 55chromite and porous 35magnetite particle developed from fine Fe rich matrix bdetails of developed porous magnetite particle with remnant of Fe silicate matrix

7 Scanning electron microscope backscattered electron micrographs showing detailed microstructures of particles in

reduced ore samples

8 a high resolution secondary electron image of surface of magnetite particle (transformed from goethite) in reduced ore

sample at 6200 000 magnification and b backscattered electron image at lower magnification showing what appear to

be nanosize alloy nuclei (bright particles)

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

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ate

pro

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no

fto

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mass-

Part

icle

Ph

asem

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lg

rou

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e

Ap

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ate

pro

po

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nin

part

icle

s

Ap

pro

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ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

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part

icle

s

22 5

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

posite

33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

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Ta

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5S

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dis

trib

uti

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inm

ajo

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nd

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ph

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tue

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by

EP

MA

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bs

erv

ed

ino

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ce

do

rea

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ed

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sa

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Part

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lg

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pn

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Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

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iin

ph

ase

N

ito

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en

tag

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ph

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ito

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P

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ph

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Lim

onite

com

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part

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limonite

com

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part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

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i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

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com

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0 9

00 1

0 2

80 1

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ine

1 2

90 5

1 5

60 4

0 6

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1 8

b

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ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

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tes

of

sm

all

part

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rich

matr

ixndash

ndashndash

ndash0 1

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3ndash

ndashndash

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1a7

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entine

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i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

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ine

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FeN

i)2S

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ndashndash

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ndashndash

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i)O

(OH

)0 8

12 7

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ndashndash

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3

mag

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3

mag

netite

(F

eN

i)O

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2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

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(F

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i)O

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2O

30 1

40 0

0 4

60 1

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5

CH

RO

MIT

E5

chro

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g)O

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0 0

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Serp

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7

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serp

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933 5

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mag

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inclu

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7a1

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H) 4

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31 7

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ine

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419 5

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8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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the magnetite particles in these systems The small sizesof the particles explain why it has not been possible topreviously resolve these alloy particles

Olivine particles

Olivine and olivine composites were observed as singlephase particles and as inclusions in the limonite com-posite particles Measurements using EPMA in Table 3and XRD results in Fig 2 suggest that the serpentinewas transformed to olivine upon reduction roasting Itappears that the serpentine was transformed to olivinefollowing reaction (2)

2(Mg Fe Ni)3Si2O5(OH)4(s)

3(Mg Fe Ni)2SiO4(s)zSiO2(s)z4H2O(g) (2)

Figure 9 shows different types of olivine and olivinecomposite particlesrsquo microstructure observed in thereduced ore sample Wide variations in the ratio ofmagnesium to iron concentration (from the Mg richforsterite to Fe rich fayalite) were observed from oneolivine particle to another Figure 9a shows a singlephase olivine particle with a relatively dense structurethis type of olivine originated from the relatively denseserpentine in the ore feed sample as shown in Fig 4a Itappeared that there is no obvious change of the structureand morphology of this type of material upon reduction

roasting other than the composition ie serpentine toolivine

Upon reduction roasting a development of magnetitewithin olivine was observed in a small proportion of theolivine particles as shown in Fig 9bndashd Figure 9c and dshows other examples of olivine with magnetite inclu-sions In contrast with Fig 9b it can be seen in Fig 9cthat in this particular particle the magnetite was evolvedalong the fissures within the porous olivine veinsFigure 9d shows in more detail the interface betweenthe formed magnetite and the parent olivine phase Itcan be seen from the image that there are regions (lightgrey phase) surrounding the magnetite phases whichmay indicate an intermediate phase This phase is afayalite olivine rich in iron 2(FeMg)OSiO2 for examplein Fig 9d the light grey phase contains 374ndash669 mass-Fe2O3 For comparison the average iron oxideconcentration in no 8b1 (olivine) phase in this parti-cular particle is 60 mass- An interesting observationfrom these results is that the formation of the magnetiteis not only on the surface or along the fissures but alsoapparently from within the inside of the particle

Other particles

Chromite and quartz were observed in the reduced oresample as single phase particles or as inclusions withinother particles The chromite and quartz particles in the

a 85olivine particle bc 8b5olivine with magnetite inclusions d details of area in vicinity of magnetite inclusions9 Scanning electron microscope backscattered electron micrographs showing microstructures of olivine and olivine

composite particles in reduced ore samples (1 limonite composite particle 8a1 olivine 8a2 serpentine 5 chromite

8b1 olivine 8b2 magnetite)

Rhamdhani et al Nickel laterite Part 1

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

140 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

4S

um

ma

ryo

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ajo

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an

dp

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ns

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ac

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am

ple

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PM

A

Ap

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Part

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Ap

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part

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s

Ap

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of

tota

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OS

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Fe

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Ni

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mass-

mass-

Lim

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rich

matr

ix67 0

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75 9

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ag

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318 0

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chro

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0 0

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serp

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2 0

0 5

18 9

39 9

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90 7

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mag

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0 0

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q

uart

z

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22 0

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glo

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tes

36 5

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ag

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of

sm

all

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rich

matr

ix68 0

24 8

0 8

2 8

79 0

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87 1

0 1

11a3

m

ag

netite

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i)O

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86 8

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1a5

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g)O

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54 7

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0 0

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1a7

serp

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FeN

i)3S

i 2O

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H) 4

2 7

1 0

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45 0

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FeN

i)2S

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0 5

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1a9

q

uart

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SiO

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0 5

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0 0

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30 0

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inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

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chro

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chro

mite

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g)O

(C

rA

lFe) 2

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50 2

15 7

0 0

60 2

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ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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by

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Part

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Ph

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lg

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Ore

feed

Red

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ore

Leach

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Perc

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tag

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onite

com

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part

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com

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s1 1

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matr

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25 4

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30 3

70 7

0 7

24 7

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1 7

serp

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1 7

94 3

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00 5

0 7

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(Mg

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i)2S

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1 3

80 6

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1 8

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com

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0 9

00 1

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1 2

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b

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with

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inclu

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ns

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0 2

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Ag

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sm

all

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rich

matr

ixndash

ndashndash

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ndashndash

ndash0 0

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i)3S

i 2O

5(O

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i)2S

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91 4

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chro

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inclu

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chro

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ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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reduced ore sample have similar structure to thechromite and quartz particles in the ore feed indicatingthat these particlesphases did not undergo any trans-formation upon reduction roasting

Other nickel bearing minerals observed in the samplewere forsterite nickeloan with nickel concentration up to202 mass-NiO which was observed in trace quanti-ties Pyroxene olivinendashpyroxene composite CandashMgndashFesilicate (diopside) gibbsite Fe silicate MgndashAl silicateand Al rich olivine were also observed in the sample intrace quantities

Leached ore sampleThe X-ray powder diffraction spectrum of the leachedores sample is also shown in Fig 2 The main com-ponents of the leached ore sample were identified to beolivine and magnetite Comparing with the XRDspectrum of the reduced ore it can be seen that thereis a decrease in the peaks associated with taenite (FendashNialloy) in the leached ore which indicates that theselective dissolution of the FendashNi alloy occurs during theleaching process

The detailed compositions of the major particles andphases observed in the leached ore sample measuredusing EPMA are presented in Table 4 The majorminor and trace phases observed in the leached ore aresimilar to that observed in the reduced ore The principaldifference is that the nickel concentrations in the phases

in the leached ore are lower than that of the same phasesin the reduced ore

Limonite composite particles

In the leached ore sample 60 of the limonitecomposite particles were found to have disintegratedThis appeared to be due to both mechanical abrasionand chemical attack upon leaching which explains theshifting of the particle size distribution shown in Fig 1Figure 10a and b shows the microstructures of thedisintegrating limonite composite particles The singlephase particles in the composite are still held together byFe rich fine grains (labelled no 1a1) but some separa-tions between some individual particles and the matrixcan be seen clearly The Fe rich fine grains are less densecompared to the original Fe rich matrix indicating thepartial dissolution of this mixture upon leaching processThe intact limonite composite retain a similar structureto the limonite composite particles in reduced ore asshown in Fig 10c and d

The Fe rich matrix (no 11) in the intact limonitecomposite particles has a slightly different compositioncompared to the Fe rich fine grains (no 1a1) that holdthe agglomerates together Overall the average nickelconcentration of the Fe rich matrix and Fe rich finegrains in the leached ore are much lower compared tothe Fe rich matrix in the reduced ore It can be seen fromTable 4 that the concentration of nickel of the Fe rich

1a1 Fe rich fine grains (disintegrated Fe rich matrix) 1a3 magnetite 1a8 olivine 11 Fe rich matrix 13 magnetite15 chromite 18 olivine 18a olivinendashserpentine composite 3 magnetite 5 chromite 8 olivine

10 Scanning electron microscope backscattered electron micrographs showing a general b more detailed microstructure

of disintegrating limonite composite particle c general limonite composite particle in leached ore samples and d

more detailed intact limonite composite particle in leached ore samples

Rhamdhani et al Nickel laterite Part 1

140 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

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Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

xim

ate

pro

po

rtio

no

fto

tal

mass-

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ap

pro

xim

ate

pro

po

rtio

nin

part

icle

s

Ap

pro

xim

ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

posite

33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

0 4

0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

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matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

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Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

eir

ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

ed

ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

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Ltd

reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

Ta

ble

4S

um

ma

ryo

fm

ajo

rp

art

icle

an

dp

ha

se

co

mp

os

itio

ns

inle

ac

he

do

res

am

ple

me

as

ure

db

yE

PM

A

Ap

pro

xim

ate

pro

po

rtio

no

fto

tal

mass-

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ap

pro

xim

ate

pro

po

rtio

nin

part

icle

s

Ap

pro

xim

ate

co

mp

osit

ion

of

tota

l

Mg

OS

iO2

Fe

2O

3C

r 2O

3A

l 2O

3N

iO

Ni

tota

lN

i

Ni

co

nte

nt

mass-

mass-

Lim

onite

com

posite

part

icle

s

22 5

01

limonite

com

posite

part

icle

s

1 1

Fe

rich

matr

ix67 0

15 1

1 9

5 1

75 9

1 8

4 2

0 3

48 2

0 0

61 3

m

ag

netite

(F

eN

i)O

Fe

2O

318 0

4 1

0 5

1 1

92 2

1 7

3 8

0 0

60 4

1 5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

2 0

0 5

8 5

0 0

25 4

53 8

11 8

0 0

70 0

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

0 5

18 9

39 9

26 2

0 4

2 1

0 9

90 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

6 0

1 4

30 5

51 4

14 7

0 3

1 7

1 1

42 5

1 8

a

oliv

inendashserp

entine

com

posite

33 4

1

serp

entine

0 5

0 1

27 9

43 7

14 0

0 2

2 5

0 1

0 1

33 4

2

oliv

ine

0 5

0 1

38 8

43 7

4 8

0 1

0 3

0 2

0 1

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

33 6

1

oliv

ine

1 8

0 4

13 9

41 3

34 0

0 4

2 4

0 2

0 2

33 6

2

mag

netite

0 2

0 0

0 7

1 6

95 2

0 8

1 5

0 0

0 0

1 9

q

uart

z

SiO

22 0

0 5

0 3

97 7

1 6

0 1

0 1

0 0

40 0

Ag

glo

mera

tes

36 5

01a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ix68 0

24 8

0 8

2 8

79 0

2 4

4 3

0 1

87 1

0 1

11a3

m

ag

netite

(F

eN

i)O

Fe

2O

322 0

8 0

1 4

4 7

86 8

1 1

4 6

0 1

21 5

1a5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

1 0

0 4

10 1

0 0

24 5

54 7

10 2

0 0

60 0

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 7

1 0

28 2

45 0

15 3

0 2

3 2

1 1

61 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

4 0

1 5

38 0

49 2

11 1

0 3

0 8

0 5

21 2

1a8

a

oliv

inendashserp

entine

com

posite

34 1

1

serp

entine

0 5

0 2

34 2

44 9

7 3

0 2

0 5

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0 4

34 1

2

oliv

ine

0 5

0 2

42 0

47 9

7 0

0 2

0 8

0 5

0 5

1a9

q

uart

z

SiO

21 3

0 5

0 2

99 0

0 7

0 0

0 0

0 0

30 0

Sp

inel

6 0

03

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

3100 0

6 0

0 1

0 8

89 3

4 6

4 7

0 0

80 8

0 0

10 5

04

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

395 0

0 5

0 2

1 4

87 0

4 6

6 6

0 0

90 1

4 2

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

5 0

0 0

11 7

0 1

20 9

48 9

18 0

0 0

40 0

2 0

05

chro

mite

5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

100 0

2 0

11 1

0 0

22 4

50 2

15 7

0 0

60 2

Oliv

ine

21 0

08

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

100 0

21 0

39 3

49 3

8 3

0 3

0 9

1 7

258 2

0 3

42 0

08a

oliv

inendash

serp

entine

com

posite

8a1

oliv

ine

(Mg

FeN

i)2S

iO4

60 0

1 2

39 1

44 7

9 7

0 1

0 3

1 2

42 4

8a2

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

40 0

0 8

32 9

42 8

8 4

0 4

2 4

1 4

11 8

5 0

08b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

95 0

4 8

31 9

44 9

15 2

0 5

1 4

1 3

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

35 0

0 3

0 8

2 7

85 3

4 6

5 7

0 1

00 0

Quart

z4 0

09

quart

z9

quart

z

SiO

2100 0

4 0

0 2

98 7

0 7

0 0

0 3

0 0

20 1

0 0

0Tota

l100

100

0 5

2

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 141

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

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ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

ed

ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

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fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

matrix and Fe rich fine grains in the leached ore are 018and 034 mass-NiO respectively while the concentra-tion in Fe rich matrix in the reduced ore is 241 mass-NiO (see Table 3)

Olivine particles

Figure 11 shows examples of microstructures of olivineobserved in the leached ore sample Single phase olivineparticles with dense (Fig 11a) and vein-like (Fig 11b)structures and olivine with magnetite inclusions(Fig 11c) were observed In general similar complexolivine microstructures as in the reduced ore samplewere observed in the leached ore sample they appearedto not undergo any transformation upon leaching

The average nickel oxide concentration of the singlephase olivine particles is 172 mass- while the averagenickel oxide concentration of similar olivine particles inthe reduced ore sample is 207 mass- In the case ofolivine with magnetite inclusions the average nickeloxide concentration is 136 mass- in contrast to278 mass- in the reduced ore It appeared that uponleaching only a small amount of nickel was leached fromthe olivine

Trace amounts of no 8a (olivinendashserpentine compo-site) particles were also observed microstructure ofwhich is shown in Fig 11d

Other particles

Quartz and chromites as single phase particles wereobserved in the leached ore and they appeared not to

undergo any transformation or reactions upon leachingDense magnetite and porousspongy magnetite (resultedfrom reduction roasting) were also appear to notundergo any transformation even though in generalthe average nickel concentration in these particles islower compared to the same materials in the reducedore Other phases observed in the leached ore sample intrace quantities include MgndashCa silicate forsterite nick-eloan some Fe silicate pyroxene and Al rich chromite

Nickel distributionTable 5 shows the summary of the nickel distribution inthe major particlesphases in the ore feed reduced oreand leached ore as measured by EPMA It can be seenfrom Table 5 that in general the nickel is associatedwith limonite composite and serpentineolivine particlesTable 6 shows the summary of the mean nickel contentsin the major particles observed in the ore feed reducedore and leached ore samples These values are thesummation of the mean nickel contents of each phase ineach particle type calculated from data in Tables 2ndash4From Table 6 the graphical representations of thenickel distribution in the particles in the ore feedreduced ore and leached ore samples were constructedas shown in Figs 12 and 13

The relative proportions of nickel between the nickelbearing particles in the ore feed reduced ore and leachedore are shown in Fig 12 In the ore feed the majority ofthe nickel are with the limonite composite (596) andthe serpentine particles (352) while in the case of

a 85olivine b 8b5olivine with magnetite inclusions c 85olivine (vein-like structure) d 8a5olivinendashserpentine particle11 Scanning electron microscope backscattered electron micrographs showing more detailed microstructure of olivine

particles in leached ore samples (other phases including 8b2 magnetite 8a1 olivine 8a2 serpentine)

Rhamdhani et al Nickel laterite Part 1

142 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

eir

ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

ed

ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

Ta

ble

5S

um

ma

ryo

fn

ick

el

dis

trib

uti

on

inm

ajo

rp

art

icle

sa

nd

inth

eir

ph

as

ec

on

sti

tue

nts

m

ea

su

red

by

EP

MA

o

bs

erv

ed

ino

refe

ed

re

du

ce

do

rea

nd

lea

ch

ed

ore

sa

mp

les

Part

icle

Ph

asem

inera

lg

rou

pn

am

e

Ore

feed

Red

uced

ore

Leach

ed

ore

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

talN

i

Perc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

P

erc

en

tag

eo

fN

iin

ph

ase

N

ito

tal

Ni

Lim

onite

com

posite

part

icle

1

limonite

com

posite

part

icle

s1 1

Fe

rich

matr

ix1 6

947 4

1 9

152 8

0 2

68 2

1 2

g

oeth

ite

(FeN

i)O

(OH

)1 1

25 4

ndashndash

ndashndash

1 3

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

70 7

0 7

24 7

0 0

50 4

1 7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 7

94 3

2 7

00 5

0 7

70 7

1 8

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

80 6

2 3

95 9

0 8

92 5

1 8

a

oliv

inendashserp

entine

com

posite

1 8

a1

serp

entine

1 8

40 7

0 9

00 1

0 2

80 1

1 8

a2

oliv

ine

1 2

90 5

1 5

60 4

0 6

80 2

1 8

b

oliv

ine

with

mag

netite

inclu

sio

ns

1 8

b1

oliv

ine

ndashndash

2 1

20 7

0 2

70 2

Ag

glo

mera

tes

1a

ag

glo

mera

tes

of

sm

all

part

icle

s1a1

Fe

rich

matr

ixndash

ndashndash

ndash0 1

47 1

1a3

m

ag

netite

(F

eN

i)O

Fe

2O

3ndash

ndashndash

ndash0 0

91 5

1a7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

ndashndash

ndashndash

0 9

11 8

1a8

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

ndashndash

0 4

11 2

1a8

a

oliv

inendashserp

entine

com

posite

1a8

a1

serp

entine

ndashndash

ndashndash

1 0

40 4

1a8

a2

oliv

ine

ndashndash

ndashndash

1 4

20 5

Goeth

ite

2

goeth

ite

2

goeth

ite

(FeN

i)O

(OH

)0 8

12 7

ndashndash

ndashndash

Sp

inel

3

mag

netite

3

mag

netite

(F

eN

i)O

Fe

2O

30 2

70 3

0 4

91 4

0 0

60 8

4

mag

netite

with

chro

mite

inclu

sio

ns

4 1

m

ag

netite

(F

eN

i)O

Fe

2O

30 1

40 0

0 4

60 1

0 0

70 1

5

CH

RO

MIT

E5

chro

mite

(FeM

g)O

(C

rA

lFe) 2

O3

0 0

70 1

0 0

50 1

0 0

50 2

Serp

entine

7

serp

entine

7

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

933 5

2 1

70 7

0 9

80 9

7a

serp

entine

with

mag

netite

inclu

sio

ns

7a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

1 3

31 7

ndashndash

ndashndash

7a2

m

ag

netite

(F

eN

i)O

Fe

2O

30 3

30 0

ndashndash

ndashndash

Oliv

ine

8

oliv

ine

8

oliv

ine

(Mg

FeN

i)2S

iO4

1 2

70 8

1 6

419 5

1 3

458 2

8a

oliv

inendashserp

entine

com

posite

8a1

serp

entine

(Mg

FeN

i)3S

i 2O

5(O

H) 4

2 0

90 7

1 8

83 6

0 9

62 4

8a2

oliv

ine

(Mg

FeN

i)2S

iO4

1 3

00 4

1 8

42 4

1 1

01 8

8b

oliv

ine

with

mag

netite

inclu

sio

ns

8b

1

oliv

ine

(Mg

FeN

i)2S

iO4

ndashndash

2 2

06 7

1 0

610 4

8b

2

mag

netite

(F

eN

i)O

Fe

2O

3ndash

ndash0 2

70 0

0 0

80 0

Quart

z9

quart

z9

quart

z

SiO

20 0

20 0

0 0

60 2

0 0

20 1

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 143

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

reduced ore most of the Ni are with limonite composite(651) and olivine particles (322) After leaching thenickel is extracted mainly from the limonite compositeparticles only a relatively small proportion of nickel isextracted from the olivine particles In the leachedsamples the proportion of nickel remaining (out of thetotal nickel in the ore) in the limonite composite andolivine particles are 248 and 728 respectively

The change in the nickel concentration in the nickelbearing particles is shown in Fig 13 It can be seenclearly that the majority of the nickel is with the limonitecomposite particles Upon leaching most of the nickel inthese particles is leached out indicated by the low nickelconcentration in the leached ore (y006 mass-Ni)The average nickel concentration of the olivine particlesin the reduced ore is y05 mass- In contrast to thelimonite composite particle upon leaching the nickelextraction from the olivine particles is low the nickelconcentration in the leached ore is 038 mass-Ni

SummaryDetailed characterisations of ore feed reduced ore andleached laterite ore samples obtained from industrialplant have been carried out using various analysistechniques Quantitative descriptions of the associationsand compositions of the materials have been developedby reconciling the measurement data with mass balanceapproach These have provided a better insight on thechanges occurring in the materials during the processingoperations in terms of structure composition and nickeldistribution at both macro- and microscopic level

The nickel laterite ore feed sample in the process wasfound to consist of composite and single phase particleswith sizes varying from 1 mm to 1 mm havingcomplex structures including composite fine grainmixture intergrowth vein-likeplate-like porous anddense microstructures

The major nickel bearing phasesparticles were foundto consist of Fe rich limonite composite particles and

serpentineolivine particles The goethite in the Fe richmatrix was transformed to plate-like and porousmagnetite upon reduction roasting Submicrometremetallic particles were formed at the free surfaces andinterspersed in the porous magnetite Upon reductionroasting the serpentine was transformed to olivine andin some of the olivine particles magnetite formation wasobserved

Upon leaching disintegration of the majority of thelimonite composite particles and degradation of some ofthe olivine particles were evident It has been shown thatthe majority of the nickel was in the Fe rich matrix andupon leaching almost all (90) of the nickel wasextracted Only a fraction of the nickel (50) wasextracted from olivine and olivine composites

Having characterised the ore feed reduced ore andleached ore samples the analysis of thermodynamic andphase transformation on these materials are carried outin Part 2 of the article

Acknowledgements

The authors would like to thank BHP Billiton Yabulurefinery for supplying the laterites used in the studiesThe authors would also like to acknowledge thefinancial support from Australian Research Counciland BHP Billiton Yabulu refinery as part of anAustralian Research Council Linkage project Theauthors would also like to thank Mr John Fittock andDr Joy Morgan (BHP Billiton Yabulu) for valuablediscussions Association Professor Paolo Vasconcelosand Dr Aaron Seeber for arranging the synchrotronX-ray powder diffraction analyses

References1 R A Bergman CIM Bull 2003 96 127ndash138

2 M Valix J Y Tang and W H Cheung Miner Eng 2001 14

1629ndash1635

3 D A Pazour World Min July 1979 50ndash54

4 M H Caron Trans AIME 1950 188 67ndash90

12 Summary of nickel distribution showing relative pro-

portion of nickel between nickel bearing particles in

ore feed reduced ore and leached ore

13 Summary of nickel distribution showing changes of

mean nickel content in each nickel bearing particle in

ore feed reduced ore and leached ore

Table 6 Summary of mean nickel content in major particles measured by EPMA observed in ore feed reduced ore andleached ore samples (in mass-)

Limonite composite particle Agglomerates Goethite Spinel Serpentine Olivine Quartz Sum

Ore feed 089 000 004 001 052 003 000 149Reduced ore 100 000 000 002 001 050 000 154Leached ore 006 006 000 001 001 038 000 052

Rhamdhani et al Nickel laterite Part 1

144 Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3

Pub

lishe

d by

Man

ey P

ublis

hing

(c)

IOM

Com

mun

icat

ions

Ltd

5 J G Reid and J E Fittock Proc Int Symp on lsquoLaterite nickelrsquo

Charlotte NC USA March 2004 TMS Paper 44 599ndash

618

6 T T Chen J E Dutrizac E Krause and R Osborne Proc Int

Symp on lsquoLaterite nickelrsquo Charlotte NC USA March 2004

TMS Paper 8 79ndash99

7 S A Gleeson R J Herrington J Durango and C A Velasquez

Econ Geol 2004 99 1197ndash1213

8 R Sen K Takahashi R Fortin D J Spottiswood and B Yarar

Int J Min Proc 1987 19 43ndash67

9 A Manceau and G Calas Am Miner 1985 70 549ndash558

10 A Manceau G Calas and A Decarreau Clay Miner 1985 20

367ndash387

11 M Maquet B D Cervelle and G Gouet Miner Deposita 1981

16 357ndash373

12 J E de Graaf Hydrometallurgy 1979 5 47ndash65

13 J E de Graaf Hydrometallurgy 1979 5 255ndash271

14 M Hayashi lsquoEffect of phase transition on reductive roasting of

nickel-bearing serpentinersquo MA thesis University of Utah Salt

Lake City UT USA 1971

15 M Valix and W H Cheung Miner Eng 2002 15 523ndash530

16 M Valix and W H Cheung Miner Eng 2002 15 607ndash612

17 M Kawahara J M Toguri and R A Bergman Metall Trans B

1988 19B 181ndash186

18 K Mitsutomi D Atmowidjojo and Yusuf Int J Miner Process

1987 19 297ndash309

19 S P Mehrotra and V Srinivasan Trans Inst Min Metall C

1994 103C 97ndash104

20 J Jandova and M Pedlik Kovove Mater 1991 6 439ndash449

21 D Chandra R E Siemens and C O Ruud J Met May 1980 26ndash33

22 O Antola L Holappa and P Paschen Min Proc Extr Metall

Rev 1995 15 169ndash179

23 M A Dungan Am Miner 1977 62 1018ndash1029

24 M J Wilson Clay Miner 2004 39 233ndash266

Rhamdhani et al Nickel laterite Part 1

Mineral Processing and Extractive Metallurgy (Trans Inst Min Metall C) 2009 VOL 118 NO 3 145