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Reductive leaching of indium-bearing zinc residue in sulfuric acid using sphalerite concentrate as reductant
Hydrometallurgy 161 (2016) 102–106
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Technical note
Reductive leaching of indium-bearing zinc residue in sulfuric acid using sphalerite concentrate as reductant Fan Zhang, Chang Wei ⁎, Zhigan Deng, Xingbin Li, Cunxiong Li, Minting Li Faculty of Metallurgy and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
a r t i c l e
i n f o
Article history: Received 16 June 2015 Received in revised form 19 January 2016 Accepted 23 January 2016 Available online 24 January 2016 Keywords: Indium-bearing zinc residue Reductive leaching Indium Zinc Sphalerite concentrate
a b s t r a c t Indium and zinc extraction from an indium-bearing zinc residue were investigated using sphalerite concentrate as a reductant in sulfuric acid medium. The effects of amount of sphalerite concentrate, sulfuric acid concentration, particle size, leaching time as well as temperature were discussed. The results showed that high indium and zinc extraction yield as well as high Fe2+/Fe3+ molar ratio could be obtained by reduction leaching of zinc residue with addition of sphalerite concentrate as a reductant. The optimal leaching condition was determined as 150 g/L H2SO4, 0.95 times of theoretic amount of sphalerite concentrate for 4 h at 90 °C while using particles in the range of 74–58 μm. The leaching efficiencies were 94.8% of indium, 96.1% of zinc and 92.8% of iron, respectively, and a Fe2+/Fe3+ molar ratio of 7.5 in the leach solution was also obtained. The process above was a viable method that effectively extracted zinc and indium and converted Fe3+ into Fe2+ at the same time. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Indium is a valuable metal used in electrical industry extensively, which used mainly as indium tin oxide-films in liquid crystal displays (Hsieh et al., 2009; Biswas et al., 2015). The main source of indium is the waste generated from the zinc industry, from which it is recovered as a by-product (Alfantazi and Moskalyk, 2003). In the conventional hydrometallurgical process of roast-leaching-electrowinning, which employed to treat zinc concentrates, more than 98% of indium and 20–30% of zinc present in material are transferred into leach residue. This residue is an important resource for recovery of indium and zinc (James et al., 2000). In the leach residue, a significant portion of the zinc and iron is in the form of zinc ferrite (ZnFe2O4), and most of the indium is present due to zinc ferrite isomorphism (Rao and Rao, 2005). The Waelz kiln process is the traditional way to treat the zinc residue for recovery zinc, indium and lead from the zinc residues. Unfortunately, this process has the drawbacks of high energy-consuming, air pollution and the resulting slag still has eco-compatibility problems (Menad et al., 2003; Huang et al., 2012; Mombelli et al., 2015). The hot acid leaching is another conventional method for recovery zinc and indium from the zinc residue (Nii and Hisamatsu, 1966a, 1966b). In the hot acid leaching process, zinc, iron, indium and other valuable metals are dissolved. While most of the iron ions in the obtained leach solution are ferric ion, in order to separate and recoverzinc and indium, jarosite precipitation for removing of ferric ion is a necessary process. However, in the case of indium, ⁎ Corresponding author. E-mail address: [email protected] (C. Wei).
http://dx.doi.org/10.1016/j.hydromet.2016.01.029 0304-386X/© 2016 Elsevier B.V. All rights reserved.
during the jarosite precipitation processes, most of indium in the leach solution was reported to the jarosite. The recovery rate of indium from the jarosite is lower (Ning and Chen, 1997; Yuan et al., 2008; Li et al., 2010). Besides hot acid leaching process, the reductive leaching is an effective method to extract zinc and indium from zinc residue. It was reported that the reducing conditions in the leaching process resulted in enhanced dissolution rates of zinc from zinc ferrite (Elgersma et al., 1992; Nii and Hisamatsu, 1966a, 1966b; Wu et al., 2012). Various electrochemical studies also confirmed it (Lu and Muir, 1988; Bhat et al., 1987). In the reductive leaching process, zinc, indium, and iron are dissolved, and ferric iron is simultaneously reduced to ferrous iron (Li et al., 2006; Markus et al., 2004). Indium in the leach solution can be efficiently selectively extracted by direct solvent extraction (Li et al., 2015). Iron in the leach solution can be removed by hematite (Riveros and Dutrizac, 1997; Yang et al., 2014). The reduction leaching processes is an effective method for minerals containing oxide of iron, nickel, cobalt and manganese (Abbruzzese, 1990; Kumar et al., 1993; Monade and Momada, 1999; Das and De Lange, 2011). Reductive leaching of metal oxide chalcopyrite, electric arc furnace dust, spent zinc-carbon batteries as well as stibnite flotation concentrate have also been reported in several studies using different acids and reductants (Dreisinger and Abed, 2002; Mahlangu et al., 2006; Furlani et al., 2009; Kim et al., 2009; Ghafarizadeh et al., 2011). However, the reduction leaching of zinc and indium from indiumbearing zinc residue using sphalerite concentrate as a reductant has barely been considered. In the present study, the reductive leaching of zinc and indium from the indium-bearing zinc residue using sphalerite concentrate as a reductant has been investigated. The aim is to provide
F. Zhang et al. / Hydrometallurgy 161 (2016) 102–106
103
an effective method of reductive leaching for extraction of zinc and indium and replace the traditional hot acid leaching process. 2. Materials and methods 2.1. Materials The indium-bearing zinc residue and sphalerite concentrate used in this work were obtained from Yunnan Province of China. The compositions of the materials were listed in Table 1. X-ray diffraction of the indium-bearing zinc residue identified zinc ferrite (ZnFe2O4) as the main mineral components in this residue (Fig. 1 (a)), and sphalerite (ZnS) and christophite ((Zn,Fe)S) as the main mineral components of sphalerite concentrate (Fig. 1(b)). 2.2. Methods A five-necked, round-bottomed flask (1 L) was fitted with a mechanical stirrer, a sample collection, a pH/Eh meter and two condenser tubes. The flask was then immersed in a water bath and maintained at the selected temperature ±1.0 °C. 570 mL of leaching solution was placed in the flask and heated to the desired temperature while being magnetically stirred (400 rpm). 50 g of indium-bearing zinc residue and the required amount of sphalerite concentrate was then added to the reactor. The addition of sphalerite (η) was evaluated by the formulas: η¼
MReal MTheory
MTheory ¼
ð1Þ
MZR C Fe 32 C S 56 2
ð2Þ
where MReal is the actual amount of sphalerite, MTheory the theoretic amount of sphalerite, MZR the amount of zinc residue, CFe the wt% of Fe in zinc residue, CS the wt% of S in sphalerite. At the end of each leaching experiment, the slurry was filtered, and the leach liquor and the solid residue were analyzed, and extractions of zinc, indium and iron were calculated from the solid chemical analysis. Zinc was analyzed by complex titration with EDTA. Indium concentration was determined by ICP with mass spectrometric detection (ICP-MS). The concentrations of ferrous ion were analyzed by complex titration with potassium dichromate. The concentrations of ferric ion were determined by finding the difference between overall iron and ferrous ion concentrations. X-ray powder diffraction was carried out using Rigaku D/MAX 2500v diffractometer (Japan). The potential of solution was measured by a platinum electrode and an Ag/AgCl electrode used as the reference electrode. 3. Results and discussion
Fig. 1. XRD of indium-bearing zinc residue (a) and sphalerite concentrate (b).
of sphalerite concentrate, the extractions were 87.8% zinc, 78.8% iron and 81.6% indium after 5 h. With 0.95 times of theoretic amount of sphalerite concentrate, the extractions of zinc, iron and indium were increased significantly to 96.4%, 93.8% and 95.8%, respectively. The zinc ferrite was dissolved in sulfuric solution as follows:
3.1. Effect of amount of sphalerite concentrate ZnFe2 O4ðsÞ þ 4H2 SO4ðaqÞ ¼ ZnSO4ðaqÞ þ Fe2 ðSO4 Þ3ðaqÞ þ 4H2 O: Fig. 2 presented the effect of amount of sphalerite concentrate on extractions of zinc, iron and indium. It can be seen from Fig. 2 that the extractions of zinc, iron and indium increased and then decreased with the increase of amount of sphalerite concentrate. In the absence
By dissolving of zinc ferrite, Fe3+ is released. The high Fe3+ concentrations retarded the dissolution of ZnFe2O4. In sulfuric acid solution, the Fe3+ was reduced to Fe2+ by sphalerite as follows: Fe2 ðSO4 Þ3ðaqÞ þ ZnSðSÞ ¼ 2FeSO4ðaqÞ þ ZnSO4ðaqÞ þ SðSÞ :
Table 1 Chemical composition of indium-bearing zinc residue and sphalerite concentrate. Components
Zn
Indium-bearing zinc residue (%) Sphalerite concentrate (%)
23.40 30.9
Fe
In(g/t) Ag(g/t) S 510
47.27 14.44 354.7
SiO2 Cu
Pb
97.2
3.75 5.72 1.00 0.64
45.7
33.08 2.43 0.74 0.061
ð3Þ
ð4Þ
By simultaneously dissolving ZnFe2O4 and converting Fe3+ to Fe2+, the dissolution of zinc ferrite will not be retarded by the presence of Fe3+, and the reaction of zinc ferrite dissolution (Eq. (3)) was shifted to the right. What is more, the activity of H+ was increased and zinc ferrite dissolution was promoted by converting Fe3+ to Fe2+ (Dimitrios and George, 1991). The extractions of zinc, iron and indium had stopped the ongoing growth when the initial amount of sphalerite was over
104
F. Zhang et al. / Hydrometallurgy 161 (2016) 102–106
Fig. 2. Effect of amount of sphalerite concentrate on extractions of Zn, Fe and In. H2SO4: 150 g/L, particle size: 74–58 μm, reaction time 5 h, 90 °C. Fig. 4. Effect of reaction time on extractions of Zn, Fe and In. Amount of sphalerite concentrate 0.95, 150 g/L H2SO4, particle size: 74–58 μm, 90 °C.
0.95. That might due to an excess of sphalerite concentrate which did not dissolve in sulfuric without ferric iron. Fig. 3 showed that the Fe3 + was decreased and the Fe2 + was increased with the amount of sphalerite concentrate increased. Due to converting Fe3 + into Fe2 +, the redox potential was decreased with amount of sphalerite concentrate increased (see Fig. 3). The sphalerite dissolution increased with concentrations of ferric iron at all redox potential values and the redox potential at all ferric iron concentrations (Song et al., 2013). It was therefore expected that apart of metal sulfide from sphalerite concentrate did not dissolve in the reductive leaching.
3.2. Effect of reaction time It was shown in Fig. 4 that the extractions of zinc, iron and indium increased from 81.5%, 65.7% and 59.7% to 96.1%, 92.8% and 94.8% when the time increased from 1 h to 4 h, respectively. But a further increase in time to 5 h had no significant affect.
Fig. 3. Effect of amount of sphalerite concentrate on redox potential of leachate and concentration of Fe3+ and Fe2+ in leachate. H2SO4: 150 g/L, particle size: 74–58μm, reaction time 5 h, 90 °C.
3.3. Effect of initial sulfuric acid concentration The results (Fig. 5) showed that the curves of leaching efficiencies of zinc, iron and indium increased faster with the increased in the initial sulfuric acid concentration from 90 g/L to 150 g/L, but slightly improved when the concentration was over 150 g/L. It also can be seen from Fig. 5 that residual H2SO4 concentration in leachate was slightly improved with the increased in the initial sulfuric acid concentration from 90 g/L to 150 g/L, but sharply improved when the concentration was over 150 g/L.
3.4. Effect of particle size It was shown from Fig. 6 that the extractions percentage of zinc, iron and indium increased as the size of particles decreased. This effect was due to the increased in the interfacial area of leaching reaction as the solid particles became smaller. In the following experiments, the particle size of the sample chosen was 74–58 μm to obtain higher extractions of metal.
Fig. 5. Effect of initial sulfuric acid concentration on extractions of Zn, Fe, In and residual H2SO4 in leachate. Amount of sphalerite concentrate 0.95, particle size: 74–58 μm, reaction time 4 h, 90 °C.
F. Zhang et al. / Hydrometallurgy 161 (2016) 102–106
105
Fig. 6. Effect of particle size on extractions of Zn, Fe and In. Amount of sphalerite concentrate 0.95, 150 g/L H2SO4, reaction time 4 h, 90 °C. Fig. 8. XRD pattern of reductive leach residue.
90 °C for 4 h, and the data indicated that under the conditions employed up to 96.1% Zn, 92.8% Fe and 94.8% In extractions were achieved. The reductive leach residue was chemically analyzed, and the results were presented in Table 2. It can be seen in Table 2 that the reductive leach residue became an Ag and S0 rich material with high SiO2. A typical XRD pattern of reductive leach residue was given in Fig. 8. It can be seen clearly in Fig. 8 that the main compositions of the reductive leach residue were elemental sulfur (S0) which was the oxidized product of sulfide sulfur, anglesite (PbSO4), sphalerite ((Zn,Fe)S) and quartz (SiO2). The zinc ferrite was almost entirely dissolved, and there was a significant part of ZnS from sphalerite in the reductive leach residue. The key point to the reductive leaching was the dissolution of sphalerite. The compositions of leachate, obtained under at same conditions, were presented in Table 3. The leach solution contained 3.2 g/L Fe3+ and 24.1 g/L Fe2+, and the molar ratio of Fe2+/Fe3+ was 7.5. The Fe3+ was lower, and the cementation of Cu from the reductive leachate by iron was viable. The indium can be recovered easily from the leachate after Fe3+ reduction. Fig. 7. Effect of temperature on extractions of Zn, Fe and In. Amount of sphalerite concentrate 0.95, 150 g/L H2SO4, particle size: 74–58 μm, reaction time 4 h.
3.5. Effect of temperature Fig. 7 showed the effect of temperature on the extractions of metal. The extractions of metal increased with increasing of temperature. The extractions of zinc, iron and indium increased from 69.8%, 65.5% and 63.1% to 96.1%, 92.8% and 94.8% when the temperature increased from 60 °C to 90 °C, respectively.
3.6. Characterization of residue and leachate from reductive leaching Reductive leach residue, obtained under conditions of the amount of sphalerite concentrate of 0.95, 150 g/L H2SO4, particle size 74–58 μm, at Table 2 Chemical compositions of reductive leach residue. Fe
In/g/t Ag/g/t
S
0
Components
Zn
Reductive leach residue(%)
6.68 13.44 173.4 775.35 41.98 28.07 16.92 0.27 5.87
S
SiO2
Cu
Pb
4. Conclusions The indium-bearing zinc residue was leached by sulfuric acid solution in the presence of sphalerite concentrate for reduction of ferric ion. Experiments data indicated that under the conditions 150 g/L H2SO4, 0.95 times of theoretic amount of sphalerite concentrate, particle size 74–58 μm, at 90 °C for 4 h up to 96.1% Zn, 92.8% Fe and 94.8% In extractions were achieved, and a Fe2+/Fe3+ molar ratio of 7.5 in the leach solution was also obtained. The reductive leaching of zinc ferrite in the presence of sphalerite concentrate as reductant was a viable process that effectively extracted zinc and indium and converted Fe3 + into Fe2 + at the same time. The main minerals of reductive leach residue were sulfur (So), anglesite (PbSO4), sphalerite ((Zn,Fe)S) and quartz (SiO2). The reductive leachate was amenable to separation of indium and zinc from iron. Zinc ferrite was almost entirely dissolved in reductive leaching. The key point to the reductive leaching was the dissolution of sphalerite concentrate. Table 3 Chemical compositions of reductive leachate. Components
Zn2+
TFe
Fe2+
Fe3+
In3+
Cu2+
H2SO4
Reductive leachate (g/L)
29.6
27.3
24.1
3.2
0.055
0.98
36.8
106
F. Zhang et al. / Hydrometallurgy 161 (2016) 102–106
Acknowledgments This research was financially supported by the National Basic Research Program of China (no. 2014CB643404), the National Natural Science Foundation of China (no. 51564030, no. 51474117, no. 51474115 and no. 51364022). References Abbruzzese, C., 1990. Percolation leaching of manganese ore by aqueous sulfur dioxide. Hydrometallurgy 25, 85–97. Alfantazi, A.M., Moskalyk, R.R., 2003. Processing of indium: a review. Miner. Eng. 16, 687–694. Bhat, K.L., Natarajan, K.A., Ramachandran, T., 1987. Electroleaching of zinc leach residues. Hydrometallurgy 18, 287–303. Biswas, N., Ghosh, P., Sarkar, S., Moitra, D., Biswas, P.K., Jana, S., Mukhopadhyay, A.K., 2015. Nanomechanical properties of dip coated indium tin oxide films on glass. Thin Solid Films 579, 21–29. Das, G.K., de Lange, J.A.B., 2011. Reductive atmospheric acid leaching of West Australian smectitic nickel laterite in the presence of sulphur dioxide and copper(II). Hydrometallurgy 105, 264–269. Dimitrios, F., George, P.D., 1991. A reaction of kinetic model for the leaching of industrial zinc ferrite particulates in sulphuric acid media. Can. J. Chem. Eng. 71, 790–801. Dreisinger, D., Abed, N., 2002. A fundamental study of the reductive leaching of chalcopyrite using metallic iron part I: kinetic analysis. Hydrometallurgy 66, 37–57. Elgersma, F., Kamst, G.F., Witkamp, G.J., Rosmalen, G.M., 1992. Acidic dissolution of zinc ferrite. Hydrometallurgy 29, 173–189. Furlani, G., Moscardini, E., Pagnaelli, F., Ferella, F., Vegliò, Toro L., 2009. Recovery of manganese from zinc aljaline batteries by reductive acid leaching using carbohydrates as reductant. Hydrometallurgy 99, 115–118. Ghafarizadeh, B., Rashchi, F., Vahidi, E., 2011. Recovery of manganese from electric arc furnace dust of ferromanganese production units by reductive leaching. Miner. Eng. 24, 174–176. Hsieh, S.L., Chen, C.C., Say, W.C., 2009. Process for recovery of indium from ITO scraps and metallurgical microstructures. Mater. Sci. Eng. B 158 (1-3), 82–87. Huang, P.C., Chi, K.H., Chen, M.L., Chang, M.B., 2012. Characteristics of dioxin emissions from a Waelz plant with acid and basic kiln mode. J. Hazard. Mater. 201-202, 229–235. James, S.E., Watson, J.L., Peter, J., 2000. Zinc production — a survey of existing smelters and refineries. Lead-Zinc 205–225. Kim, T.-H., Senanayake, G., Kang, J.-G., Sohn, J.-S., Rhee, K.-I., Lee, S.-W., Shin, S.-M., 2009. Reductive acid leaching of spent zinc–carbon batteries and oxidative precipitation of Mn–Zn ferrite nanoparticles. Hydrometallurgy 96, 154–158. Kumar, R., Das, S., Ray, R.K., Biswas, A.K., 1993. Leaching of pure and cobalt bearing goethites in sulphurous acid: kinetics and mechanism. Hydrometallurgy 32, 39–59.
Li, S.Q., Tang, M.T., He, J., Yang, S.H., Yang, S.H., Tang, C.B., Cheng, Y.M., 2006. Extraction of indium from indium-bearing zinc concentrates. Trans. Nonferrous Metals Soc. China 16, 1448–1454. Li, H.B., Zhou, Z.H., Chen, Z.F., 2010. Study on the jarosite process in zinc hydrometallurgy. Hunan Nonferrous Metals 26 (4), 27–29 (In Chinese). Li, X.B., Deng, Z.G., Li, C.X., Wei, C., Li, M.T., Fan, G., Rong, H., 2015. Direct solvent extraction of indium from a zinc residue reductive leach solution by D2EHPA. Hydrometallurgy 156, 1–5. Lu, Z.Y., Muir, D.M., 1988. Dissolution of metal ferrites and iron oxides by HCl under oxidizing and reducing conditions. Hydrometallurgy 21, 9–21. Mahlangu, T., Gudyanga, F.P., Simbi, D.J., 2006. Reductive leaching of stibnite (Sb2S3) flotation concentrate using metallic iron in a hydrochloric acid medium I: Thermodynamics. Hydrometallurgy 84, 192–203. Markus, H., Fugleberg, S., Valtakari, D., Salmi, T., Murzin, Y.D., Lahtinen, M., 2004. Reduction of ferric to ferrous with sphalerite concentrate, kinetic modelling[J]. Hydrometallurgy 73 (3), 269–282. Menad, N., Ayala, J.N., Garcia-Carcedo, F., Ruiz-Ayúcar, E., Hernández, A., 2003. Study of the presence of fluorine in the recycled fraction during carbothermal treatment of EAF dust. Waste Manag. 23 (6), 483–491. Mombelli, D., Mapelli, C., Barella, S., Gruttadauria, A., Di Landro, U., 2015. Laboratory investigation of Waelz slag stabilization. Process Saf. Environ. Prot. 94, 227–238. Monade, F.W.Y., Momada, Z.G., 1999. Reductive leaching of manganese oxide ore in aqueous methanol-sulphuric acid medium. Hydrometallurgy 51, 103–113. Nii, K., Hisamatsu, Y., 1966a. The dissolution mechanism of zinc ferrite. Trans. Nat. Res. Inst. Metals 8, 183–192. Nii, K., Hisamatsu, Y., 1966b. The promotion of acid dissolution of zinc ferrite. Trans. Nat. Res. Inst. Metals 8, 193–199. Ning, S.M., Chen, Z.F., 1997. Recovery of zinc and indium from jarosite residues. Chin. J. Nonferrous Metals 7 (3), 56–58 (In Chinese). Rao, B.P., Rao, K.H., 2005. Distribution of In3+ ions in indium-substituted Ni–Zn–Ti ferrites. J. Magn. Magn. Mater. 292, 44–48. Riveros, P.A., Dutrizac, J.E., 1997. The precipitation of hematite from ferric chloride media. Hydrometallurgy 46, 85–104. Song, J., Gao, L., Lin, J.Q., Wu, H.B., Lin, J.Q., 2013. Kinetics and modeling of chemical leaching of sphalerite concentrate using ferric iron in a redox-controlled reactor. Chin. J. Chem. Eng. 21, 933–936. Wu, X.L., Wu, S.K., Qin, W.Q., Ma, X.H., Niu, Y.J., Lai, S.S., Yang, C.G., Jiao, F., Ren, L.Y., 2012. Reductive leaching of gallium from zinc residue. Hydrometallurgy 113-114, 195–199. Yang, F., Deng, Z.G., Wei, C., Li, C.X., Li, X.B., 2014. Iron-removal by hematite form leaching liquor of high iron sphalerite. Chin. J. Nonferrous Metals 9 (24), 2387–2392 (In Chinese). Yuan, T.C., Gao, L., S.M, Ning, K.C, Zhou, 2008. Treatment on zinc concentrate with high indium and iron content by jarosite process. Nonferrous Metals 1, 11–14 (In Chinese).
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Technical note
Reductive leaching of indium-bearing zinc residue in sulfuric acid using sphalerite concentrate as reductant Fan Zhang, Chang Wei ⁎, Zhigan Deng, Xingbin Li, Cunxiong Li, Minting Li Faculty of Metallurgy and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
a r t i c l e
i n f o
Article history: Received 16 June 2015 Received in revised form 19 January 2016 Accepted 23 January 2016 Available online 24 January 2016 Keywords: Indium-bearing zinc residue Reductive leaching Indium Zinc Sphalerite concentrate
a b s t r a c t Indium and zinc extraction from an indium-bearing zinc residue were investigated using sphalerite concentrate as a reductant in sulfuric acid medium. The effects of amount of sphalerite concentrate, sulfuric acid concentration, particle size, leaching time as well as temperature were discussed. The results showed that high indium and zinc extraction yield as well as high Fe2+/Fe3+ molar ratio could be obtained by reduction leaching of zinc residue with addition of sphalerite concentrate as a reductant. The optimal leaching condition was determined as 150 g/L H2SO4, 0.95 times of theoretic amount of sphalerite concentrate for 4 h at 90 °C while using particles in the range of 74–58 μm. The leaching efficiencies were 94.8% of indium, 96.1% of zinc and 92.8% of iron, respectively, and a Fe2+/Fe3+ molar ratio of 7.5 in the leach solution was also obtained. The process above was a viable method that effectively extracted zinc and indium and converted Fe3+ into Fe2+ at the same time. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Indium is a valuable metal used in electrical industry extensively, which used mainly as indium tin oxide-films in liquid crystal displays (Hsieh et al., 2009; Biswas et al., 2015). The main source of indium is the waste generated from the zinc industry, from which it is recovered as a by-product (Alfantazi and Moskalyk, 2003). In the conventional hydrometallurgical process of roast-leaching-electrowinning, which employed to treat zinc concentrates, more than 98% of indium and 20–30% of zinc present in material are transferred into leach residue. This residue is an important resource for recovery of indium and zinc (James et al., 2000). In the leach residue, a significant portion of the zinc and iron is in the form of zinc ferrite (ZnFe2O4), and most of the indium is present due to zinc ferrite isomorphism (Rao and Rao, 2005). The Waelz kiln process is the traditional way to treat the zinc residue for recovery zinc, indium and lead from the zinc residues. Unfortunately, this process has the drawbacks of high energy-consuming, air pollution and the resulting slag still has eco-compatibility problems (Menad et al., 2003; Huang et al., 2012; Mombelli et al., 2015). The hot acid leaching is another conventional method for recovery zinc and indium from the zinc residue (Nii and Hisamatsu, 1966a, 1966b). In the hot acid leaching process, zinc, iron, indium and other valuable metals are dissolved. While most of the iron ions in the obtained leach solution are ferric ion, in order to separate and recoverzinc and indium, jarosite precipitation for removing of ferric ion is a necessary process. However, in the case of indium, ⁎ Corresponding author. E-mail address: [email protected] (C. Wei).
http://dx.doi.org/10.1016/j.hydromet.2016.01.029 0304-386X/© 2016 Elsevier B.V. All rights reserved.
during the jarosite precipitation processes, most of indium in the leach solution was reported to the jarosite. The recovery rate of indium from the jarosite is lower (Ning and Chen, 1997; Yuan et al., 2008; Li et al., 2010). Besides hot acid leaching process, the reductive leaching is an effective method to extract zinc and indium from zinc residue. It was reported that the reducing conditions in the leaching process resulted in enhanced dissolution rates of zinc from zinc ferrite (Elgersma et al., 1992; Nii and Hisamatsu, 1966a, 1966b; Wu et al., 2012). Various electrochemical studies also confirmed it (Lu and Muir, 1988; Bhat et al., 1987). In the reductive leaching process, zinc, indium, and iron are dissolved, and ferric iron is simultaneously reduced to ferrous iron (Li et al., 2006; Markus et al., 2004). Indium in the leach solution can be efficiently selectively extracted by direct solvent extraction (Li et al., 2015). Iron in the leach solution can be removed by hematite (Riveros and Dutrizac, 1997; Yang et al., 2014). The reduction leaching processes is an effective method for minerals containing oxide of iron, nickel, cobalt and manganese (Abbruzzese, 1990; Kumar et al., 1993; Monade and Momada, 1999; Das and De Lange, 2011). Reductive leaching of metal oxide chalcopyrite, electric arc furnace dust, spent zinc-carbon batteries as well as stibnite flotation concentrate have also been reported in several studies using different acids and reductants (Dreisinger and Abed, 2002; Mahlangu et al., 2006; Furlani et al., 2009; Kim et al., 2009; Ghafarizadeh et al., 2011). However, the reduction leaching of zinc and indium from indiumbearing zinc residue using sphalerite concentrate as a reductant has barely been considered. In the present study, the reductive leaching of zinc and indium from the indium-bearing zinc residue using sphalerite concentrate as a reductant has been investigated. The aim is to provide
F. Zhang et al. / Hydrometallurgy 161 (2016) 102–106
103
an effective method of reductive leaching for extraction of zinc and indium and replace the traditional hot acid leaching process. 2. Materials and methods 2.1. Materials The indium-bearing zinc residue and sphalerite concentrate used in this work were obtained from Yunnan Province of China. The compositions of the materials were listed in Table 1. X-ray diffraction of the indium-bearing zinc residue identified zinc ferrite (ZnFe2O4) as the main mineral components in this residue (Fig. 1 (a)), and sphalerite (ZnS) and christophite ((Zn,Fe)S) as the main mineral components of sphalerite concentrate (Fig. 1(b)). 2.2. Methods A five-necked, round-bottomed flask (1 L) was fitted with a mechanical stirrer, a sample collection, a pH/Eh meter and two condenser tubes. The flask was then immersed in a water bath and maintained at the selected temperature ±1.0 °C. 570 mL of leaching solution was placed in the flask and heated to the desired temperature while being magnetically stirred (400 rpm). 50 g of indium-bearing zinc residue and the required amount of sphalerite concentrate was then added to the reactor. The addition of sphalerite (η) was evaluated by the formulas: η¼
MReal MTheory
MTheory ¼
ð1Þ
MZR C Fe 32 C S 56 2
ð2Þ
where MReal is the actual amount of sphalerite, MTheory the theoretic amount of sphalerite, MZR the amount of zinc residue, CFe the wt% of Fe in zinc residue, CS the wt% of S in sphalerite. At the end of each leaching experiment, the slurry was filtered, and the leach liquor and the solid residue were analyzed, and extractions of zinc, indium and iron were calculated from the solid chemical analysis. Zinc was analyzed by complex titration with EDTA. Indium concentration was determined by ICP with mass spectrometric detection (ICP-MS). The concentrations of ferrous ion were analyzed by complex titration with potassium dichromate. The concentrations of ferric ion were determined by finding the difference between overall iron and ferrous ion concentrations. X-ray powder diffraction was carried out using Rigaku D/MAX 2500v diffractometer (Japan). The potential of solution was measured by a platinum electrode and an Ag/AgCl electrode used as the reference electrode. 3. Results and discussion
Fig. 1. XRD of indium-bearing zinc residue (a) and sphalerite concentrate (b).
of sphalerite concentrate, the extractions were 87.8% zinc, 78.8% iron and 81.6% indium after 5 h. With 0.95 times of theoretic amount of sphalerite concentrate, the extractions of zinc, iron and indium were increased significantly to 96.4%, 93.8% and 95.8%, respectively. The zinc ferrite was dissolved in sulfuric solution as follows:
3.1. Effect of amount of sphalerite concentrate ZnFe2 O4ðsÞ þ 4H2 SO4ðaqÞ ¼ ZnSO4ðaqÞ þ Fe2 ðSO4 Þ3ðaqÞ þ 4H2 O: Fig. 2 presented the effect of amount of sphalerite concentrate on extractions of zinc, iron and indium. It can be seen from Fig. 2 that the extractions of zinc, iron and indium increased and then decreased with the increase of amount of sphalerite concentrate. In the absence
By dissolving of zinc ferrite, Fe3+ is released. The high Fe3+ concentrations retarded the dissolution of ZnFe2O4. In sulfuric acid solution, the Fe3+ was reduced to Fe2+ by sphalerite as follows: Fe2 ðSO4 Þ3ðaqÞ þ ZnSðSÞ ¼ 2FeSO4ðaqÞ þ ZnSO4ðaqÞ þ SðSÞ :
Table 1 Chemical composition of indium-bearing zinc residue and sphalerite concentrate. Components
Zn
Indium-bearing zinc residue (%) Sphalerite concentrate (%)
23.40 30.9
Fe
In(g/t) Ag(g/t) S 510
47.27 14.44 354.7
SiO2 Cu
Pb
97.2
3.75 5.72 1.00 0.64
45.7
33.08 2.43 0.74 0.061
ð3Þ
ð4Þ
By simultaneously dissolving ZnFe2O4 and converting Fe3+ to Fe2+, the dissolution of zinc ferrite will not be retarded by the presence of Fe3+, and the reaction of zinc ferrite dissolution (Eq. (3)) was shifted to the right. What is more, the activity of H+ was increased and zinc ferrite dissolution was promoted by converting Fe3+ to Fe2+ (Dimitrios and George, 1991). The extractions of zinc, iron and indium had stopped the ongoing growth when the initial amount of sphalerite was over
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Fig. 2. Effect of amount of sphalerite concentrate on extractions of Zn, Fe and In. H2SO4: 150 g/L, particle size: 74–58 μm, reaction time 5 h, 90 °C. Fig. 4. Effect of reaction time on extractions of Zn, Fe and In. Amount of sphalerite concentrate 0.95, 150 g/L H2SO4, particle size: 74–58 μm, 90 °C.
0.95. That might due to an excess of sphalerite concentrate which did not dissolve in sulfuric without ferric iron. Fig. 3 showed that the Fe3 + was decreased and the Fe2 + was increased with the amount of sphalerite concentrate increased. Due to converting Fe3 + into Fe2 +, the redox potential was decreased with amount of sphalerite concentrate increased (see Fig. 3). The sphalerite dissolution increased with concentrations of ferric iron at all redox potential values and the redox potential at all ferric iron concentrations (Song et al., 2013). It was therefore expected that apart of metal sulfide from sphalerite concentrate did not dissolve in the reductive leaching.
3.2. Effect of reaction time It was shown in Fig. 4 that the extractions of zinc, iron and indium increased from 81.5%, 65.7% and 59.7% to 96.1%, 92.8% and 94.8% when the time increased from 1 h to 4 h, respectively. But a further increase in time to 5 h had no significant affect.
Fig. 3. Effect of amount of sphalerite concentrate on redox potential of leachate and concentration of Fe3+ and Fe2+ in leachate. H2SO4: 150 g/L, particle size: 74–58μm, reaction time 5 h, 90 °C.
3.3. Effect of initial sulfuric acid concentration The results (Fig. 5) showed that the curves of leaching efficiencies of zinc, iron and indium increased faster with the increased in the initial sulfuric acid concentration from 90 g/L to 150 g/L, but slightly improved when the concentration was over 150 g/L. It also can be seen from Fig. 5 that residual H2SO4 concentration in leachate was slightly improved with the increased in the initial sulfuric acid concentration from 90 g/L to 150 g/L, but sharply improved when the concentration was over 150 g/L.
3.4. Effect of particle size It was shown from Fig. 6 that the extractions percentage of zinc, iron and indium increased as the size of particles decreased. This effect was due to the increased in the interfacial area of leaching reaction as the solid particles became smaller. In the following experiments, the particle size of the sample chosen was 74–58 μm to obtain higher extractions of metal.
Fig. 5. Effect of initial sulfuric acid concentration on extractions of Zn, Fe, In and residual H2SO4 in leachate. Amount of sphalerite concentrate 0.95, particle size: 74–58 μm, reaction time 4 h, 90 °C.
F. Zhang et al. / Hydrometallurgy 161 (2016) 102–106
105
Fig. 6. Effect of particle size on extractions of Zn, Fe and In. Amount of sphalerite concentrate 0.95, 150 g/L H2SO4, reaction time 4 h, 90 °C. Fig. 8. XRD pattern of reductive leach residue.
90 °C for 4 h, and the data indicated that under the conditions employed up to 96.1% Zn, 92.8% Fe and 94.8% In extractions were achieved. The reductive leach residue was chemically analyzed, and the results were presented in Table 2. It can be seen in Table 2 that the reductive leach residue became an Ag and S0 rich material with high SiO2. A typical XRD pattern of reductive leach residue was given in Fig. 8. It can be seen clearly in Fig. 8 that the main compositions of the reductive leach residue were elemental sulfur (S0) which was the oxidized product of sulfide sulfur, anglesite (PbSO4), sphalerite ((Zn,Fe)S) and quartz (SiO2). The zinc ferrite was almost entirely dissolved, and there was a significant part of ZnS from sphalerite in the reductive leach residue. The key point to the reductive leaching was the dissolution of sphalerite. The compositions of leachate, obtained under at same conditions, were presented in Table 3. The leach solution contained 3.2 g/L Fe3+ and 24.1 g/L Fe2+, and the molar ratio of Fe2+/Fe3+ was 7.5. The Fe3+ was lower, and the cementation of Cu from the reductive leachate by iron was viable. The indium can be recovered easily from the leachate after Fe3+ reduction. Fig. 7. Effect of temperature on extractions of Zn, Fe and In. Amount of sphalerite concentrate 0.95, 150 g/L H2SO4, particle size: 74–58 μm, reaction time 4 h.
3.5. Effect of temperature Fig. 7 showed the effect of temperature on the extractions of metal. The extractions of metal increased with increasing of temperature. The extractions of zinc, iron and indium increased from 69.8%, 65.5% and 63.1% to 96.1%, 92.8% and 94.8% when the temperature increased from 60 °C to 90 °C, respectively.
3.6. Characterization of residue and leachate from reductive leaching Reductive leach residue, obtained under conditions of the amount of sphalerite concentrate of 0.95, 150 g/L H2SO4, particle size 74–58 μm, at Table 2 Chemical compositions of reductive leach residue. Fe
In/g/t Ag/g/t
S
0
Components
Zn
Reductive leach residue(%)
6.68 13.44 173.4 775.35 41.98 28.07 16.92 0.27 5.87
S
SiO2
Cu
Pb
4. Conclusions The indium-bearing zinc residue was leached by sulfuric acid solution in the presence of sphalerite concentrate for reduction of ferric ion. Experiments data indicated that under the conditions 150 g/L H2SO4, 0.95 times of theoretic amount of sphalerite concentrate, particle size 74–58 μm, at 90 °C for 4 h up to 96.1% Zn, 92.8% Fe and 94.8% In extractions were achieved, and a Fe2+/Fe3+ molar ratio of 7.5 in the leach solution was also obtained. The reductive leaching of zinc ferrite in the presence of sphalerite concentrate as reductant was a viable process that effectively extracted zinc and indium and converted Fe3 + into Fe2 + at the same time. The main minerals of reductive leach residue were sulfur (So), anglesite (PbSO4), sphalerite ((Zn,Fe)S) and quartz (SiO2). The reductive leachate was amenable to separation of indium and zinc from iron. Zinc ferrite was almost entirely dissolved in reductive leaching. The key point to the reductive leaching was the dissolution of sphalerite concentrate. Table 3 Chemical compositions of reductive leachate. Components
Zn2+
TFe
Fe2+
Fe3+
In3+
Cu2+
H2SO4
Reductive leachate (g/L)
29.6
27.3
24.1
3.2
0.055
0.98
36.8
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