The document discusses precipitating indium from pressure leaching liquor using sodium tripolyphosphate. Various factors that influence indium precipitation were evaluated, including pH, temperature, reaction time, and molar ratio of sodium tripolyphosphate to indium. Over 95% of indium was precipitated under optimal conditions of pH 2.6, reaction time of 1.5 hours, and molar ratio of sodium tripolyphosphate to indium of 0.91. X-ray diffraction analysis showed the main component of the precipitates was NaIn3(P3O10)2·12H2O.

1. 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, China
b
School of Resource and Metallurgy, Guangxi University, Nanning 530004, China
a b s t r a c ta r t i c l e i n f o
Article history:
Received 21 September 2010
Received in revised form 9 December 2010
Accepted 9 December 2010
Available online 21 December 2010
Keywords:
Sodium tripolyphosphate
Indium
Pressure leaching liquor
Recovery
The main purpose of this study was to precipitate indium and extract indium from pressure oxidative leaching
liquor using sodium tripolyphosphate. Various influential factors were evaluated in the paper, such as pH
value, 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 diffraction
analyses showed that the main component of the precipitates was NaIn3 (P3O10)2·12H2O. The resulting
precipitate was dissolved by using NaOH solution and hot sulfuric acid solution respectively, and then the
solution was subjected to solvent extraction and cementation using zinc powder for the recovery of indium.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Indium has emerged as an important strategic metal that is
extensively used in electrical industries for its excellent chemical,
physical and mechanical performance. Indium and its compounds
exhibit semiconductor or optoelectronic characteristics, which are used
in the production of liquid crystal display, semiconductor, low pressure
sodium lamp, and infrared photo-detector (Alfantazi and Moskalyk,
2003). Sphalerite presented in sulfide ores is the principle mineral
source for the Indium production (Pavia, 2001). The pressure leaching of
the indium-containing sphalerite and the behavior of indium in the
pressure leaching process have not been sufficiently investigated yet. In
acid pressure oxidative leaching of such indium-bearing sphalerite, the
treatment of indium-bearing solution must be considered. Recently,
solvent extraction of Indium (III) by different kinds of extracting agents
has been reported mainly (Alguacil, 1999; Lee et al., 2002; Liu et al.,
2006; Gao et al., 2010). A great progress has been made in the
technology for the separation of indium, but there are still many
problems needed to be solved, such as high production costs, high
energy consumption, severe environmental pollution, and so on. In
addition, strict new regulatory requirements on the use of organic
solvents worldwide, which have prompted studies relating to the
separation and enrichment of indium ions using methods such as
nanofiltration 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 and
enrichment of indium from various matrices.
The indium and iron concentrations in leach solution are in the low
and high level respectively. It is difficult to recover indium from the
leaching solution with solvent extraction directly (Tomii et al., 1981).
Therefore, an attempt was made to develop a new process to recover
indium from the pressure oxidative leaching liquor bearing indium. In
the new process, indium was first enriched by the precipitation
method using sodium tripolyphosphate (Na5P3O10), and then indium
in the precipitation was further separated and purified by solvent
extraction.
2. Experimental
2.1. Raw materials
The pressure oxidative leaching liquor was originated from
Yunnan Lancang Lead Ore Co., Ltd, Yunnan, China. The chemical
composition is described in Table 1.
As listed in Table 1, the pressure oxidative leaching liquor contains
many kinds of impurities and a great amount of Fe3+
, which makes
the recovery difficult.
2.2. Test procedures
The experiments were conducted in a batch mode by heating either
0.5 L or 1.0 L of solutions to various temperatures in the range of
25–65 °C in reaction vessels. One of the experiments was designed to
examine the extent of indium precipitation with sodium tripoly-
phosphate in the system of pressure oxidative leaching liquor bearing
Hydrometallurgy 106 (2011) 165–169
⁎ Corresponding author. Tel.: +86 13391312191; fax: +86 21 86645547.
E-mail address: haojue1016@yahoo.com.cn (Q. Zhong).
0304-386X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.hydromet.2010.12.009
Contents lists available at ScienceDirect
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journal homepage: www.elsevier.com/locate/hydromet

2. indium. The other experiments intended to investigate the influential
factors of precipitation of indium with sodium tripolyphosphate
containing Fe3+
, Fe2+
, Cu2+
, Zn2+
, Cd2+
and various initial ratio of
Na5P3O10/indium, and then the indium in the precipitation was further
isolated and purified by solvent extraction. In every experimental run,
the pH was adjusted by ZnO with a fixed stirring ratio of 150 rpm at
room temperature. The resulting pH was controlled during the
precipitation reaction. The precipitates were dried overnight at room
temperature prior to subsequent chemical and XRD analyses.
The concentration of Cu2+
, Zn2+
, Cd2+
and indium was determined
with atomic absorption spectrometry. Titration with potassium
dichromate was used to determine Fe2+
concentration. The concentra-
tion of Fe3+
was determined by the difference between overall iron and
Fe2+
concentration. All reagents were analytical pure and used without
further purification.
3. Results and discussion
3.1. Effect of pH value
Many of the papers related to the separation and enrichment of
metal ions (including indium) have been reported that one of the
critical parameters is pH (Tuzen and Soylak, 2006; Wu et al., 2004;
Chou and Yang, 2008; Liu et al., 2006). The influences of pH on the
precipitation of indium were investigated in the pH range of 1.7–3.3 in
the paper. The results acquired for precipitation of indium are
graphically depicted in Fig. 1.
It can be seen that the indium precipitation percentage with
sodium tripolyphosphate increases with increasing pH of the solution.
However, when the pH is below 2.6, acid concentration has significant
effect on precipitation of indium; while when the pH of the solution
exceeds 2.6, less significant effect on the precipitation of indium was
observed. Therefore, the best result is obtained when the pH of
solution is 2.6. It was also found that the indium precipitation
percentage without sodium tripolyphosphate is much lower than that
with sodium tripolyphosphate.
Moreover, in otherwise similar conditions, changes in temperature
did not appear to affect the extent of indium precipitation with
sodium tripolyphosphate, as the indium precipitation percentage did
not change significantly when the temperature was raised from 25 °C
to 65 °C. This indicates that the temperature has no significant effect
on indium precipitation with sodium tripolyphosphate within a
certain range.
3.2. Effect of reaction time
The relationship between the indium precipitation percentage and
reaction time was studied. The experimental conditions: temperature,
25 °C; pH, 2.6; Na5P3O10/indium mole ratio, 0.91. The reaction times
ranged from 24 min to 120 min.
The results in Fig. 2 indicate that the indium precipitation
percentage increases with increasing reaction time. However, when
reaction time exceeds 1.5 h, there is minimal effect on precipitation of
indium. Therefore, the best result is obtained when the reaction time
is 1.5 h.
3.3. Effect of Na5P3O10/indium mole ration
The molar ratio of Na5P3O10/indium was an important factor on
precipitation of indium in the pressure leaching solution. The results
are shown in Fig. 3.
The indium precipitation percentage was increased when increas-
ing the molar ratio of Na5P3O10/indium. However, when the molar
ratio of Na5P3O10/indium exceeded 0.91, the indium precipitation
percentage decreased with increasing the molar ratio of Na5P3O10/
indium. Consequently, the optimum molar ratio of Na5P3O10/indium
was 0.91.
According to Zhang and Xu (2005), the precipitation is a hydroxyl
salt when using sodium tripolyphosphate, but it can be converted into
binary salt NaIn3 (P3O10)2·12H2O. Therefore, the reactions may be
achieved as follows:
2In
3þ
þ Na5P3O10þ 10H2O ¼ In2OHP3O10⋅9H2O þ 5Na
þ
þ H
þ
ð1Þ
2In2OHP3O10⋅9H2O þ Na
þ
þ 2H
þ
¼ NaIn3ðP3O10Þ2⋅12H2O þ In
3þ
þ 8H2O
ð2Þ
Table 1
The 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
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
Inprecipitation(%)
pH
a
b
c
d
Fig. 1. Effect of pH value on precipitation of indium. a: Precipitation of indium with sodium
tripolyphosphate at 65 °C for 1.5 h; b: Precipitation of indium with sodium tripolyphosphate
at 25 °C for 1.5 h; c: Precipitation of indium without sodium tripolyphosphate at 65 °C for
1.5 h; d: Precipitation of indium with sodium tripolyphosphate at 25 °C for 1.5 h.
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
0
10
20
30
40
50
60
70
80
90
100
Inprecipitation(%)
Time (h)
Na5P3O10/In=0.91
pH=2.6
Temperature=25 C
Fig. 2. Effect of reaction time on precipitation of indium.
166 J. Jiang et al. / Hydrometallurgy 106 (2011) 165–169

3. The indium precipitation percentage decreased with increasing
molar ratio of Na5P3O10/indium, which may be achieved as follows:
NaIn3ðP3O10Þ2⋅12H2O þ 4Na5P3O10þ 12H
þ
¼ 3InðH2P3O10Þ
3À
2 þ 21Na
þ
:
ð3Þ
The following experiment was conducted to confirm the mecha-
nism proposed above. The reaction time studied was 90 min under the
operation conditions of pH=2.6, T=25 °C and molar ratio of
Na5P3O10/indium=0.91.
After reacting for 90 min, 0.15 g, 0.27 g and 0.38 g sodium
tripolyphosphate was added to the above solution each amount being
separated by 1.5 h of stirring. The pH value and the concentration of
indium in the solution were then measured.
It can be seen from Fig. 4 that amount of sodium tripolyphosphate
exerted a marked effect on precipitation of indium and the pH value of
the solution. With increasing amount of sodium tripolyphosphate,
both the concentration of indium and the pH value in the solution
increased. When amount of sodium tripolyphosphate was 0.5 g, the
concentration of indium increased from 7 mg/L to 47 mg/L and the pH
value in the solution increased from 2.6 to 3.3. This fully shows that
the precipitation of indium was dissolved again and the possible
reaction mechanism mentioned above was also proved.
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/or
bigger-ionic radius solutionsincreased,while that in lower-valence and/
or smaller-ionic radius solutions decreased, which may be due to the
competition of these metal ions. However, it was also seen that Fe3+
has
a stronger binding ability with sodium tripolyphosphate. This can have a
pronounced effect on precipitation of indium from pressure oxidative
leaching liquor bearing indium using sodium tripolyphosphate.
Therefore, Fe3+
should be reduced to Fe2+
before precipitation of
indium from solution using sodium tripolyphosphate.
In this paper, Fe3+
was reduced to Fe2+
using ZnS and the
concentration of Fe3+
was controlled below 0.041 g/L.
3.5. Microstructures and composition of indium precipitation
The interaction between indium and sodium tripolyphosphate, the
microstructures and the chemical composition of the precipitation
were studied by BSE and XRD.
A sample of the indium precipitate was polished and carbon-coated
for observation with a BSE detector. The results demonstrate that
indium-rich compound was dispersed and homogeneously distributed
in the precipitate. The results of XRD analysis indicate that the main
component of the precipitates was NaIn3 (P3O10)2·12H2O.
1.5 2.0 2.5 3.0 3.5 4.0
0
10
20
30
40
50
60
70
80
90
100Inprecipitation(%)
pH
Na5P3O10/In=0.75
Na5P3O10/In=2.07
Na5P3O10/In=0.91
Na5P3O10/In=1.07
Reaction time =1.5h
Temperature=25 C
Fig. 3. Effect of Na5P3O10/indium molar ratio on precipitation of indium.
0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55
0
10
20
30
40
50
60
70
Concentration of Indium
pH
Amount of Na5P3O10 (g)
ConcentrationofIndium(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 of
indium precipitation.
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
Pecipitation(%)
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.
Table 2
The main chemical composition of pressure oxidative leaching liquor under the
optimum condition.
Element Concentration (Final), g/L Precipitation, %
In3+
0.0031 95
Zn2+
115.11 1.95
Fe2+
7.28 1.62
Cu2+
0.389 5.06
Cd2+
0.303 2.26
Pb2+
0.794 6.59
167J. Jiang et al. / Hydrometallurgy 106 (2011) 165–169

4. According to the analysis on these results, the mechanism was
verified and therefore explaining the interaction between indium and
sodium tripolyphosphate.
3.6. Precipitation of indium from pressure leaching liquor under optimum
conditions
Based on the above experimental results, the experiment of
indium-rich pressure leaching liquor under the optimum reaction
condition was conducted. As seen in Table 2, the indium precipitation
percentage reached up to 95% when the concentration of Fe3+
was
within 0.041 g/L.
In the overall framework of precipitation of indium with sodium
tripolyphosphate in pressure leaching liquor system is one alternative
that effectively extracts indium. This shows that the enriching indium
via 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 the
hydroxide obtained was leached with sulfuric acid solution. The
solution obtained from the leaching of the precipitate is much more
appropriate for solvent extraction process (Tomii et al., 1981).
3.7.1. Experiments of extracting indium
The optimum conditions of extracting indium by D2EHPA include
an organic phase of 30 wt.% D2EHPA and 70 wt.% kerosene, a volume
phase ratio (A/O) of 3, and a temperature of 25 °C. Other required
conditions are an aqueous phase concentration of H2SO4 at 20 g/L, and
times of 5 and 10 min for vibration and setting, respectively (Li et al.,
2006). The extraction percentages of indium and iron from the
solution were 95% and 4.9% respectively.
3.7.2. Experiments on indium striping
The experiments on stripping indium were carried out under the
stripping conditions as follows: ratio of 4 between organic phase and
solution, 5 min for vibration and setting time, and a stripping agent of
sulfuric acid solution of 3 M at 25 °C (Fortes et al., 2003). The stripping
percentages of indium and iron with sulfuric acid solution are 74.50%
and 0%, respectively.
3.7.3. Experiments on cementing indium
Cementation of indium from the striping solution was performed at
a pH of 3. The reaction took place at 25 °C for a 7 h time frame. It is
important to note that the amount of zinc powder consumed was 1.8
times of the stoichiometric quantity of indium. Recovery ratio of
indium in cementation process and purity of the resulting product
were above 97%.
4. Conclusions
The results obtained show that sodium tripolyphosphate (Na5P3O10)
can be used as a reagent for enriching indium by precipitation method
from pressure oxidative leaching liquor bearing-indium. The indium
precipitation percentage was above 95% when the pH value was 2.6, the
reaction time was 1.5 h and the molar ratio of sodium tripolyphosphate
to indium was 0.91 with the concentration of Fe3+
within 0.041 g/L.
Additionally, a possible mechanism was proposed to explain the
interaction between indium and sodium tripolyphosphate. The
resulting precipitate was subsequently dissolved using NaOH and
sulfuric acid solution. The solution was then subjected to solvent
extraction and cementation processes using zinc powder to recover
indium. Total recovery ratio of indium from pressure oxidative
leaching liquor bearing-indium was more than 95%. A comparison
of the presented procedure and some current recovery of indium
methods in the literature were given in Table 3.
Acknowledgements
The authors gratefully acknowledge the support of Yunnan province
scientific foundation of China for project (Grant NO.2008049) and the
Scientific Research Foundation of Guangxi University (Grant No.
M313001).
References
Alfantazi, A.M., Moskalyk, R.R., 2003. Processing of indium: a review. Minerals
Engineering 16, 687–694.
Alguacil, F.J., 1999. Solvent extraction of indium (III) by LIX 973N. Hydrometallurgy 51,
97–102.
Chou, W.L., Yang, K.C., 2008. Effect of various chelating agents on supercritical carbon
dioxide extraction of indium(III) ions from acidic aqueous solution. Journal of
Hazardous Materials 154, 498–505.
Chou, W.L., Wang, C.T., Huang, K.Y., 2009. Electrochemical removal of indium ions
from aqueous solution using iron electrodes. Journal of Hazardous Materials 172,
46–53.
Fortes, M.C.B., Martins, A.H., Benedetto, J.S., 2003. Indium recovery from acidic aqueous
solutions by solvent extraction with D2EHPA: a statistical approach to the
experimental design. Brazilian Journal of Chemical Engineering 20, 1–5.
Gao, Z.G., Cao, Y.H., Liu, H.Z., 2010. Indium extraction process from lead soot with
indium. Chinese journal of rare metals 34, 414–419.
Lee, M.S., Ahn, J.G., Lee, E.C., 2002. Solvent extraction separation of indium and gallium
from sulphate solutions using D2EHPA. Hydrometallurgy 63, 269–276.
Li, S.Q., Tang, M.T., He, J., 2006. Extraction of indium from indium–zinc concentrations.
Transactions of the Nonferrous Metals Society of China 16, 1448–1454.
Liu, J.S., Chen, H., Chen, X.Y., Guo, Z.L., Hu, Y.C., Liu, C.P., Sun, Y.Z., 2006. Extraction and
separation of In(III), Ga(III) and Zn(II) from sulfate solution using extraction resin.
Hydrometallurgy 82, 137–143.
Pavia, A.P., 2001. Recovery of indium from aqueous solutions by solvent extraction.
Separation Science and Technology 36, 1395–1419.
Table 3
The 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 a
Chromosorb 108 resin 8–9 25 atmospheric pressure 3.78:1000(2)
95–105 b
Chelatingagents+supercritical CO2 2–3 60–70 13790 10:1(3)
90.9 c
Nanofiltration membranes 6–8 5–40 490–1470 –(1)
95 d
D2EHPA 1.4 25 Atmospheric pressure –(1)
89.7 e
P507 extraction resin 2.0 10–40 Atmospheric pressure 47.2:1000(2)
99.6 f
P204 0.4 25 Atmospheric pressure 5:1(3)
90 g
Na5P3O10 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

5. Tomii, Keishi, Annaka, Funabashi, Hideyuki, Tusuchida, 1981. Solvent extraction
recovery process for indium. US patent 4292284.
Tuzen, M., Soylak, M., 2006. A solid phase extraction procedure for indium prior to its
graphite furnace atomic absorption spectrometric determination. Journal of Hazardous
Materials B129, 179–185.
Wu, M., Sun, D.D., Tay, J.H., 2004. Effect of operating variables on rejection of indium
using nanofiltration membranes. Journal of Membrane Science 240, 105–111.
Zhang, Q.Y., Xu, K.M., 2005. Handbook of Chemistry Indium. The University of Beijing
Press, Beijing, pp. 51–55.
169J. Jiang et al. / Hydrometallurgy 106 (2011) 165–169