Hydrometallurgy 106 (2011) 165–169

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Precipitation of indium using sodium tripolyphosphate

Jibo Jiang a, Duoqiang Liang b, Qingdong Zhong a,⁎a Shanghai Key Laboratory of Modern Metallurgy and Material Processing, Shanghai University, Shanghai 200072, Chinab School of Resource and Metallurgy, Guangxi University, Nanning 530004, China

⁎ Corresponding author. Tel.: +86 13391312191; faxE-mail address: haojue1016@yahoo.com.cn (Q. Zhon

0304-386X/$ – see front matter © 2010 Elsevier B.V. Adoi:10.1016/j.hydromet.2010.12.009

a b s t r a c t

a r t i c l e i n f o

Article history:Received 21 September 2010Received in revised form 9 December 2010Accepted 9 December 2010Available online 21 December 2010

Keywords:Sodium tripolyphosphateIndiumPressure leaching liquorRecovery

Themain purpose of this study was to precipitate indium and extract indium from pressure oxidative leachingliquor using sodium tripolyphosphate. Various influential factors were evaluated in the paper, such as pHvalue, temperature, reaction time, molar ratio of Na5P3O10/indium and metal ions including Fe3+, Fe2+, Cu2+,Cd2+, Zn2+, etc. Over 95% of the indium was precipitated under the conditions employed, e.g. at a pH of 2.6,with a Na5P3O10 to indium molar ratio of 0.91, and 1.5 h reaction time. The chemical and X-ray diffractionanalyses showed that the main component of the precipitates was NaIn3 (P3O10)2·12H2O. The resultingprecipitate was dissolved by using NaOH solution and hot sulfuric acid solution respectively, and then thesolution was subjected to solvent extraction and cementation using zinc powder for the recovery of indium.

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1. Introduction

Indium has emerged as an important strategic metal that isextensively used in electrical industries for its excellent chemical,physical and mechanical performance. Indium and its compoundsexhibit semiconductor or optoelectronic characteristics, which are usedin the production of liquid crystal display, semiconductor, low pressuresodium lamp, and infrared photo-detector (Alfantazi and Moskalyk,2003). Sphalerite presented in sulfide ores is the principle mineralsource for the Indiumproduction (Pavia, 2001). Thepressure leachingofthe indium-containing sphalerite and the behavior of indium in thepressure leaching process have not been sufficiently investigated yet. Inacid pressure oxidative leaching of such indium-bearing sphalerite, thetreatment of indium-bearing solution must be considered. Recently,solvent extraction of Indium (III) by different kinds of extracting agentshas been reported mainly (Alguacil, 1999; Lee et al., 2002; Liu et al.,2006; Gao et al., 2010). A great progress has been made in thetechnology for the separation of indium, but there are still manyproblems needed to be solved, such as high production costs, highenergy consumption, severe environmental pollution, and so on. Inaddition, strict new regulatory requirements on the use of organicsolvents worldwide, which have prompted studies relating to theseparation and enrichment of indium ions using methods such asnanofiltration membranes (Wu et al., 2004), solid phase extraction(Tuzen and Soylak, 2006), supercritical CO2 extraction (Chou and Yang,2008), and electroanalytical techniques (Chou et al., 2009). However,

there is scant research on the development of the separation andenrichment of indium from various matrices.

The indium and iron concentrations in leach solution are in the lowand high level respectively. It is difficult to recover indium from theleaching solution with solvent extraction directly (Tomii et al., 1981).Therefore, an attempt was made to develop a new process to recoverindium from the pressure oxidative leaching liquor bearing indium. Inthe new process, indium was first enriched by the precipitationmethod using sodium tripolyphosphate (Na5P3O10), and then indiumin the precipitation was further separated and purified by solventextraction.

2. Experimental

2.1. Raw materials

The pressure oxidative leaching liquor was originated fromYunnan Lancang Lead Ore Co., Ltd, Yunnan, China. The chemicalcomposition is described in Table 1.

As listed in Table 1, the pressure oxidative leaching liquor containsmany kinds of impurities and a great amount of Fe3+, which makesthe recovery difficult.

2.2. Test procedures

The experiments were conducted in a batchmode by heating either0.5 L or 1.0 L of solutions to various temperatures in the range of25–65 °C in reaction vessels. One of the experiments was designed toexamine the extent of indium precipitation with sodium tripoly-phosphate in the system of pressure oxidative leaching liquor bearing

Table 1The major components and concentration of pressure oxidative leaching liquid.

Compositions In3+ Zn2+ Fe2+ Fe3+ Cu2+ Cd2+ Pb2+ As H2SO4

Concentration, g/L 0.061 117.4 7.4 5.3 0.41 0.31 0.85 0.44 37.5

166 J. Jiang et al. / Hydrometallurgy 106 (2011) 165–169

indium. The other experiments intended to investigate the influentialfactors of precipitation of indium with sodium tripolyphosphatecontaining Fe3+, Fe2+, Cu2+, Zn2+, Cd2+ and various initial ratio ofNa5P3O10/indium, and then the indium in the precipitation was furtherisolated and purified by solvent extraction. In every experimental run,the pH was adjusted by ZnO with a fixed stirring ratio of 150 rpm atroom temperature. The resulting pH was controlled during theprecipitation reaction. The precipitates were dried overnight at roomtemperature prior to subsequent chemical and XRD analyses.

The concentration of Cu2+, Zn2+, Cd2+ and indium was determinedwith atomic absorption spectrometry. Titration with potassiumdichromate was used to determine Fe2+ concentration. The concentra-tion of Fe3+was determined by the difference between overall iron andFe2+ concentration. All reagents were analytical pure and usedwithoutfurther purification.

3. Results and discussion

3.1. Effect of pH value

Many of the papers related to the separation and enrichment ofmetal ions (including indium) have been reported that one of thecritical parameters is pH (Tuzen and Soylak, 2006; Wu et al., 2004;Chou and Yang, 2008; Liu et al., 2006). The influences of pH on theprecipitation of indiumwere investigated in the pH range of 1.7–3.3 inthe paper. The results acquired for precipitation of indium aregraphically depicted in Fig. 1.

It can be seen that the indium precipitation percentage withsodium tripolyphosphate increases with increasing pH of the solution.However, when the pH is below 2.6, acid concentration has significanteffect on precipitation of indium; while when the pH of the solutionexceeds 2.6, less significant effect on the precipitation of indium wasobserved. Therefore, the best result is obtained when the pH ofsolution is 2.6. It was also found that the indium precipitationpercentage without sodium tripolyphosphate is much lower than thatwith sodium tripolyphosphate.

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4

0

10

20

30

40

50

60

70

80

90

100

In p

reci

pit

atio

n (

%)

pH

ab

c

d

Fig. 1. Effect of pH value on precipitation of indium. a: Precipitation of indiumwith sodiumtripolyphosphate at 65 °C for 1.5 h; b: Precipitationof indiumwith sodiumtripolyphosphateat 25 °C for 1.5 h; c: Precipitation of indium without sodium tripolyphosphate at 65 °C for1.5 h; d: Precipitation of indiumwith sodium tripolyphosphate at 25 °C for 1.5 h.

Moreover, in otherwise similar conditions, changes in temperaturedid not appear to affect the extent of indium precipitation withsodium tripolyphosphate, as the indium precipitation percentage didnot change significantly when the temperature was raised from 25 °Cto 65 °C. This indicates that the temperature has no significant effecton indium precipitation with sodium tripolyphosphate within acertain range.

3.2. Effect of reaction time

The relationship between the indium precipitation percentage andreaction timewas studied. The experimental conditions: temperature,25 °C; pH, 2.6; Na5P3O10/indium mole ratio, 0.91. The reaction timesranged from 24 min to 120 min.

The results in Fig. 2 indicate that the indium precipitationpercentage increases with increasing reaction time. However, whenreaction time exceeds 1.5 h, there is minimal effect on precipitation ofindium. Therefore, the best result is obtained when the reaction timeis 1.5 h.

3.3. Effect of Na5P3O10/indium mole ration

The molar ratio of Na5P3O10/indium was an important factor onprecipitation of indium in the pressure leaching solution. The resultsare shown in Fig. 3.

The indium precipitation percentage was increased when increas-ing the molar ratio of Na5P3O10/indium. However, when the molarratio of Na5P3O10/indium exceeded 0.91, the indium precipitationpercentage decreased with increasing the molar ratio of Na5P3O10/indium. Consequently, the optimum molar ratio of Na5P3O10/indiumwas 0.91.

According to Zhang and Xu (2005), the precipitation is a hydroxylsalt when using sodium tripolyphosphate, but it can be converted intobinary salt NaIn3 (P3O10)2·12H2O. Therefore, the reactions may beachieved as follows:

2In3þþ Na5P3O10þ 10H2O ¼ In2OHP3O10⋅9H2Oþ 5Naþþ Hþ ð1Þ

2In2OHP3O10⋅9H2OþNaþþ 2Hþ¼ NaIn3ðP3O10Þ2⋅12H2Oþ In3þþ 8H2O

ð2Þ

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.00

10

20

30

40

50

60

70

80

90

100

In p

reci

pit

atio

n (

%)

Time (h)

Na5P3O10/In=0.91

pH=2.6

Temperature=25 C

Fig. 2. Effect of reaction time on precipitation of indium.

1.5 2.0 2.5 3.0 3.5 4.00

10

20

30

40

50

60

70

80

90

100In

pre

cip

itat

ion

(%

)

pH

Na5P3O10/In=0.75 Na5P3O10/In=2.07Na5P3O10/In=0.91Na5P3O10/In=1.07

Reaction time =1.5h

Temperature=25 C

Fig. 3. Effect of Na5P3O10/indium molar ratio on precipitation of indium.Na(1+) K(1+) Ca(2+) Fe(2+) Zn(2+) Mg(2+) Cd(2+) Cu(2+) Pb(2+) Fe(3+) In(3+)

0

20

40

60

80

100

Pec

ipit

atio

n (

%)

Metal kinds

Fig. 5. Binding abilities of metal ions in poly-metal solution with sodium tripolyphos-phate. Complexation condition: stirring rate, 150 rpm; complexation temperature,25 °C; complexation duration, 1.5 h.

167J. Jiang et al. / Hydrometallurgy 106 (2011) 165–169

The indium precipitation percentage decreased with increasingmolar ratio of Na5P3O10/indium, which may be achieved as follows:

NaIn3ðP3O10Þ2⋅12H2Oþ 4Na5P3O10þ 12Hþ¼ 3InðH2P3O10Þ3�2 þ 21Naþ:

ð3Þ

The following experiment was conducted to confirm the mecha-nism proposed above. The reaction time studiedwas 90 min under theoperation conditions of pH=2.6, T=25 °C and molar ratio ofNa5P3O10/indium=0.91.

After reacting for 90 min, 0.15 g, 0.27 g and 0.38 g sodiumtripolyphosphate was added to the above solution each amount beingseparated by 1.5 h of stirring. The pH value and the concentration ofindium in the solution were then measured.

It can be seen from Fig. 4 that amount of sodium tripolyphosphateexerted amarked effect on precipitation of indium and the pH value ofthe solution. With increasing amount of sodium tripolyphosphate,both the concentration of indium and the pH value in the solutionincreased. When amount of sodium tripolyphosphate was 0.5 g, theconcentration of indium increased from 7 mg/L to 47 mg/L and the pHvalue in the solution increased from 2.6 to 3.3. This fully shows thatthe precipitation of indium was dissolved again and the possiblereaction mechanism mentioned above was also proved.

0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.550

10

20

30

40

50

60

70

Concentration of IndiumpH

Amount of Na5P3O10 (g)

Co

nce

ntr

atio

n o

f In

diu

m (

mg

/L)

2.7

2.8

2.9

3.0

3.1

3.2

pH

Fig. 4. Effect of amount of sodium tripolyphosphate on pH value and re-dissolving ofindium precipitation.

3.4. Behavior of other metals

The different metal ions' binding abilities with sodium tripoly-phosphate in poly-metal complexation were described in Fig. 5.

As seen in Fig. 5, different from the behavior in single-metal solution,in poly-metal solution, the binding ability in higher-valence and/orbigger-ionic radius solutions increased,while that in lower-valence and/or smaller-ionic radius solutions decreased, which may be due to thecompetition of thesemetal ions. However, it was also seen that Fe3+hasa stronger binding abilitywith sodium tripolyphosphate. This canhaveapronounced effect on precipitation of indium from pressure oxidativeleaching liquor bearing indium using sodium tripolyphosphate.Therefore, Fe3+ should be reduced to Fe2+ before precipitation ofindium from solution using sodium tripolyphosphate.

In this paper, Fe3+ was reduced to Fe2+ using ZnS and theconcentration of Fe3+ was controlled below 0.041 g/L.

3.5. Microstructures and composition of indium precipitation

The interaction between indium and sodium tripolyphosphate, themicrostructures and the chemical composition of the precipitationwere studied by BSE and XRD.

A sample of the indiumprecipitatewas polished and carbon-coatedfor observation with a BSE detector. The results demonstrate thatindium-rich compoundwasdispersed andhomogeneously distributedin the precipitate. The results of XRD analysis indicate that the maincomponent of the precipitates was NaIn3 (P3O10)2·12H2O.

Table 2The main chemical composition of pressure oxidative leaching liquor under theoptimum condition.

Element Concentration (Final), g/L Precipitation, %

In3+ 0.0031 95Zn2+ 115.11 1.95Fe2+ 7.28 1.62Cu2+ 0.389 5.06Cd2+ 0.303 2.26Pb2+ 0.794 6.59

Table 3The comparison between some current processes and the present one.

Main reagents/material Conditions Recovery(%)

Reference

pH T(°C) P(kpa) Ratio

LZX973N 3–4 20 atmospheric pressure –(1) 95 aChromosorb 108 resin 8–9 25 atmospheric pressure 3.78:1000(2) 95–105 bChelatingagents+supercritical CO2 2–3 60–70 13790 10:1(3) 90.9 cNanofiltration membranes 6–8 5–40 490–1470 –(1) 95 dD2EHPA 1.4 25 Atmospheric pressure –(1) 89.7 eP507 extraction resin 2.0 10–40 Atmospheric pressure 47.2:1000(2) 99.6 fP204 0.4 25 Atmospheric pressure 5:1(3) 90 gNa5P3O10 2.6 25–65 Atmospheric pressure 0.91:1(3) 97 This work

a:Alguacil, 1999; b:Tuzen and Soylak, 2006; c:Chou and Yang, 2008; d:Wu et al., 2004; e:Lee et al., 2002; f:Liu et al., 2006; g:Gao et al., 2010.(1) Not mentioned.(2) The saturation adsorption capabilities of In3+ (the mass ratio).(3) The molar ratio (main reagents/In).

168 J. Jiang et al. / Hydrometallurgy 106 (2011) 165–169

According to the analysis on these results, the mechanism wasverified and therefore explaining the interaction between indium andsodium tripolyphosphate.

3.6. Precipitation of indium from pressure leaching liquor under optimumconditions

Based on the above experimental results, the experiment ofindium-rich pressure leaching liquor under the optimum reactioncondition was conducted. As seen in Table 2, the indium precipitationpercentage reached up to 95% when the concentration of Fe3+ waswithin 0.041 g/L.

In the overall framework of precipitation of indium with sodiumtripolyphosphate in pressure leaching liquor system is one alternativethat effectively extracts indium. This shows that the enriching indiumvia precipitation method that uses sodium tripolyphosphate(Na5P3O10) from pressure leaching liquor is a viable process.

3.7. Recovery of indium from the precipitate

The precipitate was dissolved with NaOH solution. Then thehydroxide obtained was leached with sulfuric acid solution. Thesolution obtained from the leaching of the precipitate is much moreappropriate for solvent extraction process (Tomii et al., 1981).

3.7.1. Experiments of extracting indiumThe optimum conditions of extracting indium by D2EHPA include

an organic phase of 30 wt.% D2EHPA and 70 wt.% kerosene, a volumephase ratio (A/O) of 3, and a temperature of 25 °C. Other requiredconditions are an aqueous phase concentration of H2SO4 at 20 g/L, andtimes of 5 and 10 min for vibration and setting, respectively (Li et al.,2006). The extraction percentages of indium and iron from thesolution were 95% and 4.9% respectively.

3.7.2. Experiments on indium stripingThe experiments on stripping indium were carried out under the

stripping conditions as follows: ratio of 4 between organic phase andsolution, 5 min for vibration and setting time, and a stripping agent ofsulfuric acid solution of 3 M at 25 °C (Fortes et al., 2003). The strippingpercentages of indium and iron with sulfuric acid solution are 74.50%and 0%, respectively.

3.7.3. Experiments on cementing indiumCementation of indium from the striping solutionwas performed at

a pH of 3. The reaction took place at 25 °C for a 7 h time frame. It isimportant to note that the amount of zinc powder consumed was 1.8times of the stoichiometric quantity of indium. Recovery ratio of

indium in cementation process and purity of the resulting productwere above 97%.

4. Conclusions

The results obtained show that sodium tripolyphosphate (Na5P3O10)can be used as a reagent for enriching indium by precipitation methodfrom pressure oxidative leaching liquor bearing-indium. The indiumprecipitation percentagewas above 95%when the pH valuewas 2.6, thereaction timewas 1.5 h and themolar ratio of sodium tripolyphosphateto indium was 0.91 with the concentration of Fe3+ within 0.041 g/L.

Additionally, a possible mechanism was proposed to explain theinteraction between indium and sodium tripolyphosphate. Theresulting precipitate was subsequently dissolved using NaOH andsulfuric acid solution. The solution was then subjected to solventextraction and cementation processes using zinc powder to recoverindium. Total recovery ratio of indium from pressure oxidativeleaching liquor bearing-indium was more than 95%. A comparisonof the presented procedure and some current recovery of indiummethods in the literature were given in Table 3.

Acknowledgements

The authors gratefully acknowledge the support of Yunnan provincescientific foundation of China for project (Grant NO.2008049) and theScientific Research Foundation of Guangxi University (Grant No.M313001).

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