Research Article Investigations into Recycling Zinc...

Research ArticleInvestigations into Recycling Zinc from Used Metal OxideVaristors via pH Selective Leaching Characterization Leachingand Residue Analysis

Toni Gutknecht1 Anna Gustafsson1 Christer Forsgren2

Christian Ekberg1 and Britt-Marie Steenari1

1 Industrial Materials Recycling Department of Chemical Engineering Chalmers University of TechnologyKemivagen 4 412 96 Gothenburg Sweden2Stena Metall AB Fiskhamnsgatan 8D Box 4088 400 40 Gothenburg Sweden

Correspondence should be addressed to Toni Gutknecht tonigchalmersse

Received 12 May 2015 Accepted 5 August 2015

Academic Editor Fernando Pelisser

Copyright copy 2015 Toni Gutknecht et alThis is an open access article distributed under the Creative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Metal oxide varistors (MOVs) are a type of resistor with significantly nonlinear current-voltage characteristics commonly used inpower lines to protect against overvoltages If a proper recycling plan is developed MOVs can be an excellent source of secondaryzinc because they contain over 90 weight percent zinc oxide The oxides of antimony bismuth and to a lesser degree cobaltmanganese and nickel are also present in varistors Characterization of the MOV showed that cobalt nickel and manganese werenot present in the varistor material at concentrations greater than one weight percent This investigation determined whether a pHselective dissolution (leaching) process can be utilized as a starting point for hydrometallurgical recycling of the zinc in MOVsThis investigation showed it was possible to selectively leach zinc from the MOV without coleaching of bismuth and antimonyby selecting a suitable pH mainly higher than 3 for acids investigated It was not possible to leach zinc without coleaching ofmanganese cobalt and nickel It can be concluded from results obtained with the acids used acetic hydrochloric nitric andsulfuric that sulfate leaching produced the most desirable results with respect to zinc leaching and it is also used extensively inindustrial zinc production

1 Introduction

It is the vision for Europe to havemarket and policy incentivesin place by 2020 that will stimulate new innovations inresource efficient production methods with all companiesbeing able to measure their lifecycle resource efficiency [1]It is with this vision that the importance of this work comesto light Electrical transmission and distribution equipmentsuch as insulators and protective equipment will become apotentially large source of solid waste suitable for recycling asopposed to landfilling Recycling of the used varistor mate-rial and production waste promotes sustainable productionand consumption Moreover improving waste managementmakes better use of resources while encouraging less depen-dence on imports of raw material [1]

In Sweden there is an initiative to recycle MOV asopposed to landfilling due to environmental concerns risingcosts of landfilling awareness of the potential value of thematerial in the MOV and the quantity of material availablefor recycling In Sweden from 2009 to 2013 over 500 tons ofMOV was available for recycling [2] However a commercialmethod for recycling of the MOV is not yet available and thematerial is at the moment stored or landfilled If the ZnOwaspurified and converted to zinc metal the value of the metalliczinc would be over $800000 USD [3] The used varistors areprimarily not mixed with other types of waste materials butkept in a separate flow which is a good starting point for arecycling process The authors have not found any literatureon recycling of MOVs

Hindawi Publishing Corporatione Scientific World JournalVolume 2015 Article ID 653219 11 pageshttpdxdoiorg1011552015653219

2 The Scientific World Journal

MOVs are made by combining powdered metal oxidesof zinc antimony bismuth manganese nickel and cobaltThemetal oxide powder is sintered in a process during whichthree main microstructural phases form ZnO grains anantimony-rich phase and a bismuth-rich intergranular phase[4ndash6] The ZnO grain phase is by far the most dominantregion due to the MOV being composed mostly of zincoxide [7] The antimony-rich phase resulting from sinteringand reactions between the metal oxides has been known toinclude a pyrochlore phase as well as a spinel phase eachwith different stoichiometry [8 9] Pyrochlore is a zinc-bismuth-antimony-oxide (Zn

2Bi3Sb3O12) [10] and the other

a spinel phase containing both a cubic (Zn233

Sb067

O4) and

an orthorhombic (Zn7Sb2O12) configuration [11] Initially

Sb2O3is added to the startingmaterial to decrease the average

size of the ZnO grains [5 9 12]The current-voltage behaviorof the MOV is attributed mainly to the presence of Bi

2O3[9]

which also strongly alters the sintering behavior by producinga liquid phase with ZnO enabling liquid phase sintering [13ndash15]

It has been reported in literature that metal oxides such asMnO2 NiO andCo

2O3and otherminormetal oxidesmay be

present in the MOV added to enhance the characteristics ofthe MOV [4 5 12ndash15] Typically MOV contains greater than90mol ZnO and around 3mol of both Bi

2O3and Sb

2O3

with the other metal oxides accounting for the remaining4mol [15 16]

This work investigates the feasibility of selectively leach-ing zinc from the MOV at a certain pH as an initialstep for recovery of secondary zinc Optimal zinc leachingwould avoid coleaching of antimony bismuth and otherminor metals present in the MOV making the leachate easyto integrate into industrial zinc electrowinning solutionsIndustrially sulfuric acid is used in zinc production and itwas therefore investigated in this work as well as other acidsincluding acetic acid which is a weak monoprotic organicacid nitric acid and hydrochloric acid

In general there are two routes available for industrialzinc purification and production First a high temperaturepyrometallurgical process where activated charcoal is addedto the zinc oxide containing material and heated to tem-peratures above 1000∘C at which point zinc is vaporizedThe zinc vapor is condensed and collected either as ZnOor impure zinc which is further refined electrolytically [1718] It is known that even low concentrations of antimonyin the electrolyte can reduce the current efficiency of zincelectrowinning by nearly 80 [19] and that other impuritiessuch as cobalt nickel and manganese can also reduce thecurrent efficiency Ideally an acid and pH which only leachedzinc would be preferred but it is known from other literaturedata that leaching of antimony and cobalt will probablyinterfere in leaching of the MOVmaterial [19ndash21]

The second route is hydrometallurgical purification ofZnO feedmaterial which produces around 80 of the worldrsquoszinc [18 22] and is typically preferred over pyroprocessingdue to the effectiveness process flexibility and low tempera-tures Pyrometallurgical processes are typically energy inten-sive and often need a dust collection or gas cleaning system

[23] When choosing either a pyroprocess or hydroprocessfor recycling MOV the preferred method will have to beeconomically feasible with respect to the costs of purchasingraw startingmaterialsThere is a plethora of literature reviewsand articles on zinc recovery from industrial waste [23] butthis is the first of its kind on recovery of zinc from recycledMOV

2 Materials and Methods

21 Characterization Identification and composition of theadditives in the specific type of MOV investigated needed tobe determined as only the major metal oxides zinc bismuthand antimony were known Additives or impurities (anymetal other than zinc or ZnO) in the MOV sample mayhave an impact on zinc leaching and the eventual electrolyticprocess New MOVs approximately 70mm in diameter andweighing 1000 g were broken up into pieces approximately2 cm in diameter An impact mill was used for furtherparticle size reduction The crushed MOV was mechanicallysieved In leaching experiments material having a particlesize smaller than 63 120583m was used (100 minus250 Mesh) Forleaching smaller particle sizes equate to higher surface areaand quicker leaching kinetics are typically observed

The appearance of the ground and sieved MOV wasanalyzed with a scanning electron microscope (SEM) withenergy dispersive X-ray (EDX) spectroscopic element detec-tion (Hitachi TM 3000 with EDX Quantax 70) to obtainqualitative data about the elements present and to determinethe occurrence and distribution of the components X-raypowder diffractometry (XRD) (Bruker 2D Phaser) equippedwith a characteristic Cu radiation source and a scintillationdetector was used to identify crystalline compounds presentin the MOV powder Compound identification was madeby comparisons with standards in the Joint Committee ofPowder Diffraction Standards database [24]

To determine the metal content in the MOV completedissolution of the MOV powder was performed in triplicateusing concentrated hydrochloric acid at an elevated temper-ature The MOV material (approximately 25 g) was heatedwith 50mL concentrated hydrochloric acid (37) at 70 plusmn3∘C for 12 h while being continuously stirred using a mag-netic stir bar Before determination of metal concentrationsaliquots of the solutions were diluted with a 1M nitric acidsolution prepared from concentrated stock solution (65Suprapur Merck) and ultrapure water (Milli-Q Milliporegt18MΩcm) Analysis was done using Inductive CoupledPlasma with Optical Emission Spectrometric detection (ICP-OES) (iCAP 6500 Thermo Fischer) External calibrationcurves made by dilution of 1mgmL standard solutions wereused to quantify metal contents

22 Leaching Leaching experiments were started by mixing05 g of powdered MOV and 50mL of milli-Q water in astraight wall 150mL capacity titration vessel The vessel wasequipped with a pH electrode a stir bar and a dosing deviceconnected to a Metrohm 905 Titrando titrator connected toa computer for monitoring and controlling the acid addition

The Scientific World Journal 3

Acid was titrated into the MOV-water mixture resulting in aleachate with a specified pH

Small aliquots of the leachate were taken at times 0 2 1030 60 120 and 240minutes in each leaching experimentThepH was controlled using a silversilver chloride (AgAgCl)glass electrode Calibration of the pH electrode was doneweekly using Metrohmn Ion analysis buffer solutions of pH4 7 and 9 while the measured pH value was not correctedto compensate for changes in the ionic strength as the ionicstrength of this solution is lower than 1 The temperature ofthe system was maintained at 25∘C plusmn 1

In total four acid solutions were used for the leachingstudies acetic acid (ge997 Sigma Aldrich) hydrochloricacid (37 Sigma Aldrich) nitric acid (65 SuprapurMerck) and sulfuric acid (950ndash980) Leaching experi-ments were carried out at constant pH of 1 3 and 5 foreach acid solution with the exception of acetic acid in whichleaching experiments were carried out having final pH 2 3and 5 The acid leaching solutions were not initially preparedto the desired pH Rather the desired pH was entered intothe titration program and a more concentrated acid solutionwas added to the water-MOV system until the desired pHof the system was reached The system was stirred so thestagnant layer around the solid particles could be perturbedensuring mass transport from the liquid in the pores to theouter leachate where the pH and metal concentrations weremeasured

In order to determine the concentration of the leachedmetals as a function of time an aliquot taken at each point oftime was centrifuged and diluted with 1M HNO

3for further

analysis using ICP-OESThe following metals were analyzedBi Co Cu Fe Mg Mn Ni Sb and Zn However Cu Feand Mg were not detected and are therefore not reportedLeaching experimentswere done in triplicate to ensure exper-imental reproducibility of leaching and leaching equipmentand to account for deviation and error propagation in themeasurements The concentrations of metals in the leachateswere compared to the concentration of the metals from thecomplete dissolution experiments allowing for data to bepresented as the fraction of each metal leached

Because each acid has the ability to form complexeswith metal ions the speciation of zinc was also consideredin each acid solution The software used for speciation ofmetal ions in the leachates PHREEQC [25] using theminteqdatabase provided data on the metal-anion complexes forzinc but did not have information available on complexationof bismuth or antimony PHREEQC is a computer programused to model equilibrium and dissolution reactions [26]Concentration of zinc and acid ions in solution at the end ofthe leaching experiment (pH 1 3 and 5) were used as inputdata

3 Results and Discussion

31 Characterization of MOV The MOV used in this studywas purchased from a commercial varistor production com-pany The assumption is made that the composition of thevaristor does not change over its useful life at least on

Table 1 Chemical composition of MOV

Metal oxide mol wt Bi2O3

234 plusmn 006 51 plusmn 01Co2O3

116 plusmn 003 094 plusmn 002MnO

2076 plusmn 002 052 plusmn 001

NiO 089 plusmn 002 079 plusmn 002Sb2O3

321 plusmn 008 44 plusmn 01ZnO 916 plusmn 33 882 plusmn 31

the macroscopic scale On a microscopic (monolayer) scaleit has been shown by Stucki et al 1987 [27] that the oxygenconcentration at the interface region between ZnO graindecreases

Literature suggests that varistors may containmetal addi-tives (in the oxide form) such as cobalt chromium coppermagnesium manganese nickel sulfur antimony titaniumtungsten and yttrium [4 9 12ndash14] However the dissolvedMOV investigated only contained in detectible amounts themetals listed in Table 1 given in weight percent (wt) andmol of each metal along with the standard deviation of themeasurements

A SEM micrograph of the pulverized (particle size lessthan 63 120583m) MOV is shown in Figure 1(a) From this micro-graph three phases can be seen within the MOV Phase Ithe most dominant region was that of the zinc oxide grainsPhase II was the small particles around the zinc oxide mostlikely the antimony-rich phase which according to literatureincludes two phases pyrochlore and spinel Phase III was thewhite bismuth-rich phase An elemental map was acquiredusing the EDXdetector and is shown in Figure 1(b)The greenarea depicts the ZnO grains the purple area is the antimony-rich phase and the pink area is the bismuth-rich phase

The microstructure of the MOV is polycrystalline mak-ing it somewhat complicated to analyze the compositioneach phase having different dopants dopant concentrationsshape and size Separation by recycling of the individualmetals from the Sb-rich phases may be more complex thanleaching of metal ions from the metal oxides Eventuallythis may lead to reduced yield and slower kinetics duringleaching compared to whether only pure metal oxides hadbeen present However from Figure 1(a) it can be seen thatthe zinc oxide phase is the dominating phase and leaching ofzinc is of main importance in this study

The result from qualitative mineralogical analysis of theMOV using XRD was a spectrum as shown in Figure 2Peaks correlating to ZnO (e) Bi

2O3(X) Zn

233Sb067

O4(◻)

Zn2Bi3Sb3O14

(permil) and Zn7Sb2O12

(◼) are labeled Peaksfor compounds containing cobalt manganese and nickeloxides are not visible due to their low concentrations inthe MOV The majority of peaks shown in Figure 2 are dueto the ZnO XRD pattern There was no peak correlationfor antimony oxide confirming that antimony is present inthe spinel (Zn

233Sb067

O4and Zn

7Sb2O12) or pyrochlore

(Zn2Bi3Sb3O14) phases Some peaks correspond to multiple

compounds and are labeled accordingly


Phase IPhase II

Phase III

2014-06-25 N 20120583mtimes50k

(a) (b)

Figure 1 (a) SEM micrograph of pulverized MOV prior to leaching depicting three phases present (I) ZnO grains (II) Sb-rich phase and(III) Bi-rich phase (b) EDX map of varistor material seen in Figure 1(a) with zinc bismuth and antimony-rich phases

10 20 30 40 50 60 702120579

ZnOMetal oxide varistor

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

Figure 2 XRD spectra of the MOV showing peaks for ZnO (e)Bi2O3(X) Zn

233Sb067

O4(◻) Zn

2Bi3Sb3O14


(◼)

32 Leaching By leaching the MOV in oxidizing acids(nitric and sulfuric acids) a nonoxidizing acid (hydrochloricacid) and a weak acid (acetic acid) it was expected that aclearer picture of the leaching behavior of zinc bismuth andantimony would be determined

321 Acetic Acid Acetic acid (HAc) was very effective for theleaching of zinc fromMOV as shown in Figure 3The leachedfraction of zinc (◻) bismuth (I) and antimony (998779) is shownon the left ordinate while the right ordinate along with thesolid line shows the amount of the HAc solution added tothe MOV-water slurry to obtain the desired pH When usingHAc solutions at pH higher than 2 up to 90 of the zinc wasleached within 4 hours as shown in Figure 3(b) for pH 3 andFigure 3(c) for pH5Acetic acidwas also effective for leachingbismuth (Figure 3(a)) but to a much lesser extent antimony

where le20 of Sb was leached in pH 2 solution The resultsshow that Zn can be selectively leached with no coleaching ofSb or Bi by using an acetic acid leaching solution with pH 5

Speciation of zinc regardless of the pH in the rangeused here was approximately 44 Zn(O

2CCH3)2 24Zn2+

21 Zn(O2CCH3)+ and 11 Zn(O

2CCH3)3

minusThe dominantbismuth ions are most likely BiOH2+ BiO+ or a bismuthoxide acetate complex and not Bi3+ based on the pH of thesolution [28]

As for the other metals present in the MOV over 90 ofthe cobalt was leached in the pH 2 solution with the amountof cobalt leached decreasing with increasing pH Nickel andmanganese were both leached around 40 in pH 2 solutionsand showed the same trend as cobalt of decreased leachingwith increasing pH

322 Hydrochloric Acid Leaching with pH 1 hydrochloricacid (HCl) solution yielded 955 plusmn 31 leaching of zincfrom the MOV while it was much more difficult to leachbismuth (20 plusmn 10) and antimony (37 plusmn 6) at the same pHHowever the results show that zinc can be selectively leachedleaving both bismuth and antimony in the MOV residue byusing hydrochloric acid leaching solution with a pH higherthan 1 Results for hydrochloric acid leaching are shown inFigure 4(a) for pH 1 Figure 4(b) for pH 3 and Figure 4(c) forpH 5

In HCl solutions with pH greater than 1 Sb2O3is not

soluble and therefore remains as a solid which is consistentwith literature [25] For Bi

2O3the dominant species are

predicted using119864ℎ-pH diagrams to be Bi3+ at pH lt 2 whereas

at pH values gt 2 dominant species can be either BiOH2+BiO+ or a bismuth oxychloride complex depending on pH[28] However from the present results it appears that theoxides of Bi and Sb present in the MOV are only soluble inhydrochloric acid solutions when the pH is higher than 1This may be due to formation of nonporous and amorphoussintered phases for which the leaching of constituent metalions is physically hindered As was shown in Figure 1 bismuthis mainly present as a sintered phase between the ZnO grains


0 50 100 150 200 250Time (min)

00

02

04

06

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10

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tion

leac

hed

00

50

100

150

200

250

300

ZnBi

SbVo

lum

e add

ed (m

L)174M HAc

(a) pH 2

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02

04

06

08

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Frac

tion

leac

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00

50

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(mL)

ZnBi

Sb10M HAc

(b) pH 3

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hed

00

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ZnBi

Sb1M HAc

(c) pH 5

Figure 3 The leached fraction as given by the left ordinate for zinc (◻) bismuth (I) and antimony (998779) from MOV in (a) pH 2 (b) pH 3and (c) pH 5 solutions The volume of acetic acid (HAc) added is shown as a solid black line corresponding to the right ordinate

The speciation of zinc in hydrochloric acid solutions ascalculated by PHREEQC indicates that Zn2+ is the mostdominant species in the hydrochloric acid based leachatesobtained here In the pH 5 hydrochloric solution Zn2+accounted for approximately 92 of all zinc species but as thepH of the acidic leachate decreased to pH 1 the free Zn2+ con-centration in solution decreased due to the formation of zinc-chloride complexes Other zinc-chloride species predicted tobe present in pH 1 chloride solutions include ZnCl+ (11)ZnCl2(2) ZnCl

3

minus (03) and ZnCl4

minus2 (15)

Not only were hydrochloric acid solutions efficient forzinc leaching they also worked relatively well for the leach-ing of manganese nickel and especially cobalt In pH 1hydrochloric acid solution the percent of cobalt leached was86 whereas close to 70 and 62 of nickel and manganeserespectively were leached Thus HCl leaching did not give aselective leaching of zinc

323 Nitric Acid Leaching of MOV in pH 1 3 and 5 nitricacid (HNO

3) solutions yielded results as shown in Figure 5


0 50 100 150 200 25000

02

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06

08

10

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tion

leac

hed

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00

20

40

60

80

100

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me a

dded

(mL)

ZnBi

Sb5M HCl

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

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00

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(mL)

ZnBi

Sb5M HCl

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

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00

20

40

60

80

100

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me a

dded

(mL)

ZnBi

Sb1M HCl

(c) pH 5

Figure 4The leached fraction as given by the left ordinate for zinc (◻) bismuth (I) and antimony (998779) fromMOV in (a) pH 1 (b) pH 3 and(c) pH 5 solutions The volume of hydrochloric acid (HCl) added is shown as a solid black line corresponding to the right ordinate

for zinc bismuth and antimony For selective leaching ofzinc pH 1 nitric acid solutions work well due to the highleaching rate for zinc and low leaching of bismuth and anti-mony Bismuth showed an atypical leaching behavior as seenin Figure 5(a) Shkolrsquonikov has reported [29] precipitation ofbismuth(III) hydroxy salts near an approximate pH of 16 andsuch a reaction may explain the leaching behavior of bis-muth(III) in nitrate solutions The hydrolyzable bismuth(III)cations have been predicted by thermodynamic calculations

to be in solution in more acidic conditions [29] In pH 5solutions leaching of alkaline components still occurred at theend of the 4-hour experiment

Less than 35of themanganese contentwas leached fromtheMOV in the pH 1 nitric acid solution while 50 and 76 ofthe nickel and cobalt respectively were leached at the samepH Lower amounts of all these metals manganese nickeland cobalt were leached at lower concentrations of nitricacid that is pH 3 and 5


0 50 100 150 200 25000

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tion

leac

hed

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00

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me a

dded

(mL)

ZnBi

Sb5M HNO3

(a) pH 1

100

Frac

tion

leac

hed

0 50 100 150 200 25000

02

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06

08

10

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20

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(mL)

ZnBi

Sb1M HNO3

(b) pH 3

Frac

tion

leac

hed

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08

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me a

dded

(mL)

ZnBi

Sb1M HNO3

(c) pH 5

Figure 5The leached fraction as given by the left ordinate for zinc (◻) bismuth (I) and antimony (998779) fromMOV in (a) pH 1 (b) pH 3 and(c) pH 5 solutions The volume of nitric acid (HNO

3) added is shown as a solid black line corresponding to the right ordinate

324 Sulfuric Acid Leaching of MOV in sulfuric acid solu-tions with pH 1 3 and 5 gave results as shown in Figures 6(a)6(b) and 6(c) respectively Unlike the previously describedacid leaching experiments carried out in this work sulfuricacid solutions were able to leach all Zn at each pH level testedIncreasing the pH from 3 to 5 will not change the percentof Zn leached but rather the time needed for leaching willbe longer It seems to be feasible to use pH 3 solutions toselectively leach zinc while avoiding coleaching of antimonyand bismuth Bismuth is leached when using pH 1 solutionand the dominant species should be Bi3+ based on the 119864

ℎ-pH

diagrams [28] In these conditions less than 5 of antimonywas leached which is consistent with published data sayingthat oxidizing acidic solutions should not react with Sb

2O3

[28]PHREEQC calculations showed that approximately 65

of the zinc in the pH 1 leachate occurred as Zn2+ with theremaining 35 of zinc in solution as ZnSO

4soluble complex

The pH increased the fraction of zinc as Zn2+ ions decreased55 for pH 5

Impurities in the zinc leachate include cobalt of whichapproximately 65 was leached in all solutions investigated


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Sb2M H2SO4

(a) pH 1Fr

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Sb2M H2SO4

(b) pH 3

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Sb1M H2SO4

(c) pH 5

Figure 6The leached fraction as given by the left ordinate for zinc (◻) bismuth (I) and antimony (998779) fromMOV in (a) pH 1 (b) pH 3 and(c) pH 5 solutions The volume and concentration of sulfuric acid (H

2SO4) added is shown as a solid black line corresponding to the right

ordinate

Manganese and nickel were approximately 25 leached in pH1 solution 17 at pH 3 solution and 27 at pH 5 It is notknownwhat causes a lower leaching fraction in pH 3 solutionbut it could be due to a change in speciation or precipitationof the metals to secondary compounds

As shown it was possible to selectively leach Zn fromthe MOV without significant coleaching of bismuth andantimony by selecting a suitable pH mainly higher than 3in all acids investigated here It was not possible to leachzinc without coleaching of manganese cobalt and nickel

However such minor contaminations can be removed beforeelectrowinning of zinc by cementation

33 Analysis of Leaching Residue It was concluded thatsulfate leaching produced the most desirable results withrespect to zinc leaching and coleaching of other metals ionsas well as its extensive use in industrial zinc production Itwas also important to determine if zinc leaching was dueto bulk leaching of the ZnO grain or if the zinc within thepyrochlore and spinel phaseswas also leached thus destroying


2014-06-24 N 20120583mtimes50k

Figure 7 SEMmicrograph of pulverizedMOV after leaching in pH1 sulfuric acid solution for 240 minutes The Sb-rich phase remainsalong with some undissolved Bi-rich phase

the spinel phase and liberating antimony The insolubleresidue remaining after leaching of the MOV in a pH 1sulfuric acid solution for 240 minutes is shown in Figure 7This specimen corresponds to the leaching data in Figure 6(a)where nearly all of the zinc 80of the bismuth and very littleantimony had been leached from the MOV In Figure 7 thedominating structures present are the antimony-rich phasesIt occurs in particles of approximately 2 120583m in diameterwith some residual undissolved bismuth-rich white phaseattached The SEM micrographs in Figures 1 and 7 illustratethe before and after experimental leaching data of Figure 6

XRD analysis results for the pH 1 sulfuric acid leachingresidue (Figure 6(a)) are shown in Figure 8 as the solidblack line (mdash) The majority of the peaks can be identi-fied as originating from antimony containing compoundssuch as Zn

233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067

O4(e) The four aforementioned

chemical compounds all share the same peaks and are allpossibly present in the MOV It might be possible that theconcentrations of the minor metals (Co Ni and Mn) in theleaching residue identify the presence of some compoundscontaining Ni Co and Mn However XRD only suggest thepresence is possible not that the compound is actually in thesample

Also present in the MOV are Zn2Bi3Sb3O14

(permil) andBi2O3(X) both having identical peaks It is most logical

based on characterization and literature data that pyrochlore(Zn2Bi3Sb3O14) and spinel both cubic (Zn

233Sb067

O4) and

orthorhombic (Zn7Sb2O12) as well as the as well as the

residual Bi2O3are present residual Bi

2O3are present in the

sample It is also probable to have the presence of cobaltnickel and manganese in the sample however the chemicalform of those metals is not known The presence of minormetal oxides is typical of sintered material The spectrumfor the starting material contained prominent peaks for ZnOwhereas the appearance of ZnO peaks in the leaching residuewas nonexistent The XRD result also shows that it will bedifficult to solubilize the zinc that is present in the combinedzinc-antimony oxides

10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4

Figure 8 XRD spectrum (mdash) of leaching residue (pH 1 sulfuricacid) compared to XRD spectrum of nonleached starting material(- - -) Chemical compounds are represented as follows Bi

2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)

To summarize in total four acids were investigated eachat three different pH levels Typically pH 1 pH 3 and pH 5were used except in the case of acetic acid where pH 1 wasdifficult to obtain and pH 2 was used instead Acetic acidleaching results show that selective leaching of zinc from theMOVwith respect to bismuth and antimony can be achievedusing leaching solution with a pH 5 However in pH 5 aceticacid solutions some bismuth (13 plusmn 01) was leached Inhydrochloric acid solutions zinc can be successfully selec-tively leached from bismuth and antimony in pH 5 solutionsSimilar results for selective leaching of zinc occur in nitricacid solutions with no bismuth or antimony detected in pH5 solutions With acetic hydrochloric and nitric acid thepercent of zinc leached decreased with increasing pH

For acetic acid nearly 90 of the zinc was leachedat pH 2 3 and 5 while all zinc could be leached usinghydrochloric nitric and sulfuric acid at pH 1 Increase in pH5 in hydrochloric and nitric acid solutions resulted in lowerzinc leaching with approximately 82 and 78 zinc leachedrespectively Minor metal coleaching at pH 5 is summarizedin Table 2 From this data it is shown that leaching withHNO

3gives the lowest coleaching percentage of the minor

metals present in the MOV but industrially it is not usedin zinc production When comparing sulfuric acid with theothers it performs well The amount of cobalt coleached wasaround 66 while Mn and Ni were coleached at 27 and25 respectively The minor metal impurities would have tobe removed before Zn electrowinning

Finally leaching in sulfuric acid solutions was highlyeffective for zinc leaching at each of the three pH investigatedLeaching at pH 3 resulted in a leachate pure of antimonyand bismuth however the minor metals given in Table 2


Table 2 Percentage of minor metals coleached with zinc in pH 5leaching solutions

Acid Co Mn NiCH3COOH 745 plusmn 04 234 plusmn 01 196 plusmn 03

HCl 726 plusmn 55 231 plusmn 29 185 plusmn 09HNO

3633 plusmn 07 197 plusmn 03 170 plusmn 02

H2SO4


will require further purification of the leachate It is rec-ommended that this acid be used in recycling of the MOVbecause of the widespread industrial use of sulfate solutionsin zinc electrowinning

Regardless of the leachate used acetic hydrochloricnitric or sulfuric acid further purification of the leachate isrequired if it is to be used in the zinc electrowinning processA purificationmethod such as cementationwould be effectivefor removing antimony bismuth nickel and cobalt from theleaching solution Antimony has the added benefit of beingan activator in cementation by increasing the kinetics of thecementation reaction [30]

Speciation modeling using PHREEQC of the zinc in eachacid demonstrated that the most prominent form of Zn isZn2+ This is important because the state of the zinc andknowledge of its complexes can affect further zinc recyclingsteps such as cementation or electrowinning

4 Conclusions

This work set out to determine whether it is possible toseparate metal components of the MOV via pH selectiveleaching in acetic nitric hydrochloric and sulfuric acidicsolutions having pH 1 3 and 5 Initially the composition ofthe MOV was determined in order to quantify the metalswithin the MOV The MOV contains simple oxides such aszinc oxide but it also contains more complex oxides such asZn7Sb2O12as shown using the SEM and XRD

Experimental data showed that lower pH acid solutionsgave higher percent of zinc leaching except for the case whereH2SO4was used and zinc was shown to be fully leached

at pH 5 and below It was possible to selectively leach Znfrom theMOVwithout significant coleaching of bismuth andantimony by selecting a suitable pH mainly higher than 3in all acids investigated here It was not possible to leachzinc without coleaching of manganese cobalt and nickelEven though these metals are present in small amounts inthe leachate production of pure zinc metal will require theirremoval Sulfuric acid leaching is also preferred becausenearly 80 of zinc is produced by electrowinning in sulfatesolutions

This investigation concludes that either acetic nitrichydrochloric or sulfuric acid solutions at pH 5 can be usedto selectively leach zinc from the MOV without significantcoleaching of antimony or bismuth However the efficiencyof zinc leached decreases with increasing leaching pH exceptin the case of sulfate solution Regardless of the pH in sulfateleaching 100 of the zinc in the MOV was leached makingthis the ideal selective leaching solution for leaching zinc

from MOV Selective zinc leaching with respect to minormetals such as cobalt nickel and manganese could notbe successfully done with the acids and pH range underinvestigation in this study

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Theauthors of this work would like to thank fellow colleaguesMarcus Hedberg andMikael Karlsson for their contributionsto this work Funding was provided by Chalmers Area ofAdvance Production which is gratefully acknowledged

References

[1] European Commission ldquoRoadmap to a resource efficientEuroperdquo in Communication from the Commission to the Euro-pean Parliment the Council the European Economic and SocialCommittee and the Committee of the Regions European Com-mission Brussels Belgium 2013

[2] H Hultgren Varistor Material Information edited by T Gut-knecht Microsoft Outlook 2014

[3] LME ldquoLME Zincrdquo 2014 httpwwwlmecomen-gbmetalsnon-ferrouszinc

[4] M A Ashraf A H Bhuiyan M A Hakim and M T HossainldquoMicrostructure and electrical properties of Ho

2O3doped

Bi2O3-based ZnO varistor ceramicsrdquo Physica B Condensed

Matter vol 405 no 17 pp 3770ndash3774 2010[5] J C Kim and E Goo ldquoMorphology and formation mechanism

of the pyrochlore phase in ZnO varistor materialsrdquo Journal ofMaterials Science vol 24 no 1 pp 76ndash82 1989

[6] E R Leite M A L Nobre E Longo and J A VarelaldquoMicrostructural development of ZnO varistor during reactiveliquid phase sinteringrdquo Journal of Materials Science vol 31 no20 pp 5391ndash5398 1996

[7] R Sekula T Ruemenapp M Ljuslinder and B Doser ldquoFora better environment recycling opportunities for insulatingcomponentsrdquo in ABB Review P Terwiesch and N Leffler EdsABB Asea Brown Boveri Zurich Switzerland 2009

[8] J Wong ldquoMicrostructure and phase transformation in a highlynon-Ohmic metal oxide varistor ceramicrdquo Journal of AppliedPhysics vol 46 no 4 pp 1653ndash1659 1975

[9] M L Arefin F Raether D Dolejs and A Klimera ldquoPhaseformation during liquid phase sintering of ZnO ceramicsrdquoCeramics International vol 35 no 8 pp 3313ndash3320 2009

[10] J Kim T Kimura and T Yamaguchi ldquoSintering of zinc oxidedoped with antimony oxide and bismuth oxiderdquo Journal of theAmerican Ceramic Society vol 72 no 8 pp 1390ndash1395 1989

[11] G C Miles and A R West ldquoPyrochlore phases in the systemZnO-Bi

2O3-Sb2O5 II Crystal structures of Zn

2Bi308

Sb292

O14+120575

and Zn2+xBi296minus(119909minus119910)Sb304minus119910O1404+120575rdquo Solid State Sciences vol 8

no 12 pp 1422ndash1429 2006[12] S Bernik S Macek and A Bui ldquoThe characteristics of ZnOndash

Bi2O3-based varistor ceramics doped with Y

2O3and varying

amounts of Sb2O3rdquo Journal of the EuropeanCeramic Society vol

24 no 6 pp 1195ndash1198 2004


[13] Y Huang M Liu Y Zeng and C Li ldquoThe effect of secondaryphases on electrical properties of ZnO-based ceramic filmsprepared by a sol-gel methodrdquo Journal of Materials ScienceMaterials in Electronics vol 15 no 8 pp 549ndash553 2004

[14] Y Q Huang L Meidong Z Yike L Churong X Donglinand L Shaobo ldquoPreparation and properties of ZnO-basedceramic films for low-voltage varistors by novel sol-gel processrdquoMaterials Science and Engineering B Solid-State Materials forAdvanced Technology vol 86 no 3 pp 232ndash236 2001

[15] E Olsson ldquoInterfacial microstructure in ZnO varistor mate-rialsrdquo in Physics p 50 Chalmers University of TechnologyGoteborg Sweden 1988

[16] R Sekula M Wnek and S Slupek ldquoPotential utilizationmethod of scrap ceramic insulatorsrdquo Journal of Solid WasteTechnology and Management vol 26 no 2 p 6 1999

[17] F Habashi ldquoA short history of hydrometallurgyrdquo Hydrometal-lurgy vol 79 no 1-2 pp 15ndash22 2005

[18] R B Gordon T E Graedel M Bertram et al ldquoThe characteri-zation of technological zinc cyclesrdquoResources Conservation andRecycling vol 39 no 2 pp 107ndash135 2003

[19] A Nelson W Wang G P Demopoulos and G Houlachi ldquoTheremoval of cobalt from zinc electrolyte by cementation a criticalreviewrdquo Mineral Processing and Extractive Metallurgy Reviewvol 20 no 4 pp 325ndash356 2000

[20] D Yang G Xie G Zeng J Wang and R-X Li ldquoMechanismof cobalt removal from zinc sulfate solutions in the presence ofcadmiumrdquo Hydrometallurgy vol 81 no 1 pp 62ndash66 2006

[21] T M Dreher A Nelson G P Demopoulos and D FilippouldquoThe kinetics of cobalt removal by cementation from anindustrial zinc electrolyte in the presence of Cu Cd Pb Sb andSn additivesrdquo Hydrometallurgy vol 60 no 2 pp 105ndash116 2001

[22] F Habashi Handbook of Extractive Metallurgy Primary Metalsvol 2 of edited by F Habashi VCH Verlagsgesellschaft Wein-heim Germany 1997

[23] M K Jha V Kumar and R J Singh ldquoReview of hydromet-allurgical recovery of zinc from industrial wastesrdquo ResourcesConservation and Recycling vol 33 no 1 pp 1ndash22 2001

[24] Joint Committee of Powder Diffraction Standards JCPDS-ICCD 2010 Philadelphia Pa USA 2010

[25] Interactive P Implements PHREEQC 312 in 3128538 USGSEditor 2014

[26] S R Charlton and D L Parkhurst ldquoModules based on thegeochemical model PHREEQC for use in scripting and pro-gramming languagesrdquo Computers amp Geosciences vol 37 no 10pp 1653ndash1663 2011

[27] F Stucki P Bruesch and F Greuter ldquoElectron spectroscopicstudies of electrically active grain boundaries in ZnOrdquo SurfaceScience vol 189-190 pp 294ndash299 1987

[28] M Pourbaix Atlas of Electrochemical Equilibria in AqueousSolutions National Association of Corrosion Engineers 1974

[29] E V Shkolrsquonikov ldquoThermodynamic characterization of theamphoterismof oxidesM

2O3(M=As Sb Bi) and their hydrates

in aqueousmediardquoRussian Journal of AppliedChemistry vol 83no 12 pp 2121ndash2127 2010

[30] B S Boyanov V V Konareva and N K Kolev ldquoPurification ofzinc sulfate solutions from cobalt and nickel through activatedcementationrdquo Hydrometallurgy vol 73 no 1-2 pp 163ndash1682004

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


MOVs are made by combining powdered metal oxidesof zinc antimony bismuth manganese nickel and cobaltThemetal oxide powder is sintered in a process during whichthree main microstructural phases form ZnO grains anantimony-rich phase and a bismuth-rich intergranular phase[4ndash6] The ZnO grain phase is by far the most dominantregion due to the MOV being composed mostly of zincoxide [7] The antimony-rich phase resulting from sinteringand reactions between the metal oxides has been known toinclude a pyrochlore phase as well as a spinel phase eachwith different stoichiometry [8 9] Pyrochlore is a zinc-bismuth-antimony-oxide (Zn

2Bi3Sb3O12) [10] and the other

a spinel phase containing both a cubic (Zn233

Sb067

O4) and

an orthorhombic (Zn7Sb2O12) configuration [11] Initially

Sb2O3is added to the startingmaterial to decrease the average

size of the ZnO grains [5 9 12]The current-voltage behaviorof the MOV is attributed mainly to the presence of Bi

2O3[9]

which also strongly alters the sintering behavior by producinga liquid phase with ZnO enabling liquid phase sintering [13ndash15]

It has been reported in literature that metal oxides such asMnO2 NiO andCo

2O3and otherminormetal oxidesmay be

present in the MOV added to enhance the characteristics ofthe MOV [4 5 12ndash15] Typically MOV contains greater than90mol ZnO and around 3mol of both Bi

2O3and Sb

2O3

with the other metal oxides accounting for the remaining4mol [15 16]

This work investigates the feasibility of selectively leach-ing zinc from the MOV at a certain pH as an initialstep for recovery of secondary zinc Optimal zinc leachingwould avoid coleaching of antimony bismuth and otherminor metals present in the MOV making the leachate easyto integrate into industrial zinc electrowinning solutionsIndustrially sulfuric acid is used in zinc production and itwas therefore investigated in this work as well as other acidsincluding acetic acid which is a weak monoprotic organicacid nitric acid and hydrochloric acid

In general there are two routes available for industrialzinc purification and production First a high temperaturepyrometallurgical process where activated charcoal is addedto the zinc oxide containing material and heated to tem-peratures above 1000∘C at which point zinc is vaporizedThe zinc vapor is condensed and collected either as ZnOor impure zinc which is further refined electrolytically [1718] It is known that even low concentrations of antimonyin the electrolyte can reduce the current efficiency of zincelectrowinning by nearly 80 [19] and that other impuritiessuch as cobalt nickel and manganese can also reduce thecurrent efficiency Ideally an acid and pH which only leachedzinc would be preferred but it is known from other literaturedata that leaching of antimony and cobalt will probablyinterfere in leaching of the MOVmaterial [19ndash21]

The second route is hydrometallurgical purification ofZnO feedmaterial which produces around 80 of the worldrsquoszinc [18 22] and is typically preferred over pyroprocessingdue to the effectiveness process flexibility and low tempera-tures Pyrometallurgical processes are typically energy inten-sive and often need a dust collection or gas cleaning system

[23] When choosing either a pyroprocess or hydroprocessfor recycling MOV the preferred method will have to beeconomically feasible with respect to the costs of purchasingraw startingmaterialsThere is a plethora of literature reviewsand articles on zinc recovery from industrial waste [23] butthis is the first of its kind on recovery of zinc from recycledMOV

2 Materials and Methods

21 Characterization Identification and composition of theadditives in the specific type of MOV investigated needed tobe determined as only the major metal oxides zinc bismuthand antimony were known Additives or impurities (anymetal other than zinc or ZnO) in the MOV sample mayhave an impact on zinc leaching and the eventual electrolyticprocess New MOVs approximately 70mm in diameter andweighing 1000 g were broken up into pieces approximately2 cm in diameter An impact mill was used for furtherparticle size reduction The crushed MOV was mechanicallysieved In leaching experiments material having a particlesize smaller than 63 120583m was used (100 minus250 Mesh) Forleaching smaller particle sizes equate to higher surface areaand quicker leaching kinetics are typically observed

The appearance of the ground and sieved MOV wasanalyzed with a scanning electron microscope (SEM) withenergy dispersive X-ray (EDX) spectroscopic element detec-tion (Hitachi TM 3000 with EDX Quantax 70) to obtainqualitative data about the elements present and to determinethe occurrence and distribution of the components X-raypowder diffractometry (XRD) (Bruker 2D Phaser) equippedwith a characteristic Cu radiation source and a scintillationdetector was used to identify crystalline compounds presentin the MOV powder Compound identification was madeby comparisons with standards in the Joint Committee ofPowder Diffraction Standards database [24]

To determine the metal content in the MOV completedissolution of the MOV powder was performed in triplicateusing concentrated hydrochloric acid at an elevated temper-ature The MOV material (approximately 25 g) was heatedwith 50mL concentrated hydrochloric acid (37) at 70 plusmn3∘C for 12 h while being continuously stirred using a mag-netic stir bar Before determination of metal concentrationsaliquots of the solutions were diluted with a 1M nitric acidsolution prepared from concentrated stock solution (65Suprapur Merck) and ultrapure water (Milli-Q Milliporegt18MΩcm) Analysis was done using Inductive CoupledPlasma with Optical Emission Spectrometric detection (ICP-OES) (iCAP 6500 Thermo Fischer) External calibrationcurves made by dilution of 1mgmL standard solutions wereused to quantify metal contents

22 Leaching Leaching experiments were started by mixing05 g of powdered MOV and 50mL of milli-Q water in astraight wall 150mL capacity titration vessel The vessel wasequipped with a pH electrode a stir bar and a dosing deviceconnected to a Metrohm 905 Titrando titrator connected toa computer for monitoring and controlling the acid addition






3for further

















2O3(X) Zn

233Sb067

O4(◻)

Zn2Bi3Sb3O14



233Sb067

O4and Zn





Phase IPhase II

Phase III

2014-06-25 N 20120583mtimes50k

(a) (b)


10 20 30 40 50 60 702120579


Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12


233Sb067

O4(◻) Zn

2Bi3Sb3O14


(◼)





2CCH3)2 24Zn2+


2CCH3)3










0 50 100 150 200 250Time (min)

00

02

04

06

08

10

Frac

tion

leac

hed

00

50

100

150

200

250

300

ZnBi

SbVo

lum

e add

ed (m

L)174M HAc

(a) pH 2

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb10M HAc

(b) pH 3

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb1M HAc

(c) pH 5



3


minus2 (15)





0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HCl

(c) pH 5






0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HNO3

(a) pH 1

100

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(c) pH 5




ℎ-pH


2O3



4soluble complex




0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb1M H2SO4

(c) pH 5



ordinate






2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






3for further

















2O3(X) Zn

233Sb067

O4(◻)

Zn2Bi3Sb3O14



233Sb067

O4and Zn





Phase IPhase II

Phase III

2014-06-25 N 20120583mtimes50k

(a) (b)


10 20 30 40 50 60 702120579


Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12


233Sb067

O4(◻) Zn

2Bi3Sb3O14


(◼)





2CCH3)2 24Zn2+


2CCH3)3










0 50 100 150 200 250Time (min)

00

02

04

06

08

10

Frac

tion

leac

hed

00

50

100

150

200

250

300

ZnBi

SbVo

lum

e add

ed (m

L)174M HAc

(a) pH 2

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb10M HAc

(b) pH 3

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb1M HAc

(c) pH 5



3


minus2 (15)





0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HCl

(c) pH 5






0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HNO3

(a) pH 1

100

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(c) pH 5




ℎ-pH


2O3



4soluble complex




0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb1M H2SO4

(c) pH 5



ordinate






2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Phase IPhase II

Phase III

2014-06-25 N 20120583mtimes50k

(a) (b)


10 20 30 40 50 60 702120579


Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12


233Sb067

O4(◻) Zn

2Bi3Sb3O14


(◼)





2CCH3)2 24Zn2+


2CCH3)3










0 50 100 150 200 250Time (min)

00

02

04

06

08

10

Frac

tion

leac

hed

00

50

100

150

200

250

300

ZnBi

SbVo

lum

e add

ed (m

L)174M HAc

(a) pH 2

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb10M HAc

(b) pH 3

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb1M HAc

(c) pH 5



3


minus2 (15)





0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HCl

(c) pH 5






0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HNO3

(a) pH 1

100

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(c) pH 5




ℎ-pH


2O3



4soluble complex




0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb1M H2SO4

(c) pH 5



ordinate






2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 50 100 150 200 250Time (min)

00

02

04

06

08

10

Frac

tion

leac

hed

00

50

100

150

200

250

300

ZnBi

SbVo

lum

e add

ed (m

L)174M HAc

(a) pH 2

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb10M HAc

(b) pH 3

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

Frac

tion

leac

hed

00

50

100

150

200

250

300

Volu

me a

dded

(mL)

ZnBi

Sb1M HAc

(c) pH 5



3


minus2 (15)





0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HCl

(c) pH 5






0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HNO3

(a) pH 1

100

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(c) pH 5




ℎ-pH


2O3



4soluble complex




0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb1M H2SO4

(c) pH 5



ordinate






2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HCl

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HCl

(c) pH 5






0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HNO3

(a) pH 1

100

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(c) pH 5




ℎ-pH


2O3



4soluble complex




0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb1M H2SO4

(c) pH 5



ordinate






2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb5M HNO3

(a) pH 1

100

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

20

40

60

80

100

Volu

me a

dded

(mL)

ZnBi

Sb1M HNO3

(c) pH 5




ℎ-pH


2O3



4soluble complex




0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb1M H2SO4

(c) pH 5



ordinate






2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 50 100 150 200 25000

02

04

06

08

10

Frac

tion

leac

hed

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(a) pH 1Fr

actio

n le

ache

d

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb2M H2SO4

(b) pH 3

Frac

tion

leac

hed

0 50 100 150 200 25000

02

04

06

08

10

Time (min)

00

10

20

30

40

50

Volu

me a

dded

(mL)

ZnBi

Sb1M H2SO4

(c) pH 5



ordinate






2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


2014-06-24 N 20120583mtimes50k




233Sb067

O4(◻) Zn

7Sb2O12(◼) ZnCo

133Sb067

O4

(I) and Zn166

Ni067

Sb067






233Sb067

O4) and





10 20 30 40 50 60 70

Leachate residueMOV

2120579

Bi2O3

Bi3Sb3Zn2O14

Zn233Sb067O4

Zn7Sb2O12

ZnCo133Sb067O4

Zn166Ni067Sb067O4


2O3(X)

Zn233

Sb067

O4(◻) and Zn

7Sb2O12(◼)











H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






H2SO4





4 Conclusions








Acknowledgments


References





2O3doped











2Bi308

Sb292

O14+120575




2O3and varying


24 no 6 pp 1195ndash1198 2004































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

Research Article Investigations into Recycling Zinc...

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