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In this study, hydrometallurgical processes involving pressure acid leaching and solvent extraction were developed to aid recovery of indium from zinc slag, which is produced in the imperial smelting process. Four different acid leaching methods were studied, namely atmospheric leaching, atmospheric leaching with KMnO4, roasting-atmospheric leaching, and oxygen pressure leaching in a sulfuric acid medium. Oxygen pressure acid leaching is the most effective method for indium extraction, and 94.1% of indium was leached under the optimum conditions, i.e., 300 g/L H2SO4,oxygen pressure 0.4 MPa, liquid/solid ratio 10 mL/g, and temperature 100°C for 5 h. X-ray diffraction and scanning electron microscopy examination of the raw material and leaching residue samples indicated that the intermetallic compounds Cu5Zn8and Cu2Zn, metallic zinc, and iron in the raw material dissolved, leaving the insoluble components PbSO4 and Pb as the major compounds in the leaching residue. A 98.5% proportion of the indium in the leaching solution was selectively extracted with 30% bis(2-ethylhexyl) phosphate and 70% kerosene by three-stage counter-current extraction, and 99.5% of the indium in the loaded organic phase was stripped by 6 mol/L HCl through four-stage counter-current stripping. The overall recovery yield of indium through all processes was approximately 92%. [ABSTRACT FROM AUTHOR]

The separation and recovery of copper and indium from a solution arising from the reductive leaching of a zinc leaching residue was studied. Copper was enriched into a copper precipitate produced by iron powder precipitation; indium was hydrolyzed and enriched into a gypsum indium precipitate produced by limestone adjustment of pH. Separation and recovery of both copper and indium were achieved. The results showed that precipitation of copper(II) and arsenic(III) as Cu2O and Cu3As is thermodynamically feasible by adding iron powder to the reductive leach of a zinc leaching residue. Increasing the iron powder addition and reaction temperature promoted the formation of Cu2O and Cu3As. In the process of neutralizing and precipitating indium by adjusting the pH using limestone, indium was mainly concentrated in the precipitate by hydrolytic precipitation. The pH of the neutralization endpoint plays a decisive role in this hydrolytic enrichment. The extent of indium precipitation exceeded 98%, and the indium content of the precipitate reached 3.6 kg/t. Addition of limestone balances the acid across the entire production process. The main phase in the gypsum indium precipitate was CaSO4·2H2O, the stable properties of which create favorable conditions for the recovery of indium in subsequent steps. [ABSTRACT FROM AUTHOR]

Abstract: The mineralogical analysis of a sphalerite concentrate by electron-microprobe shows that the main indium-bearing minerals are pyrite, zinckenite, galena, cassiterite, jamesonite. The kinetics of indium dissolution from sphalerite concentrate in the sulphuric acid–oxygen system indicated that the particle size, temperature and sulphuric acid concentration significantly influenced the leaching efficiencies of indium. The experimental data indicated that under the conditions employed up to 92% indium extraction were achieved. The empirical kinetic model, −ln(1− x)= kt was used to describe the dissolution kinetics of indium in sulphuric acid solutions, and the results showed that indium dissolution process was controlled by chemical reaction with the activation energies calculated to be 47kJ/mol and the reaction order with respect to sulphuric acid concentration closed to 1. [Copyright &y& Elsevier]

Abstract: The leaching of a sphalerite concentrate with high indium and iron content in sulfuric acid–oxygen media has been studied in the present paper. The variables considered in the study were particle size, concentration of sulfuric acid, partial pressure of oxygen, leaching temperature, and leaching time. The experimental data indicated that under the conditions employed up to 99% zinc and 90% indium extraction were achieved. The mineralogical analysis of the residue showed that the main minerals are elemental sulphur, unreacted pyrite and quartz, the amount of sulphide sulphur oxidized to sulphate during leaching is 81%. [Copyright &y& Elsevier]

A direct solvent-extraction process was developed to selectively recover indium from solutions generated by reductive leaching of zinc residues. This approach avoids the traditional steps of intermediate precipitation, solid–liquid separation, and re-leaching. Copper in the leach solution is easily removed by cementation with iron powder and the remaining Fe(III) is reduced to the ferrous state, which avoids the possibility of its co-extraction with indium. Indium is effectively extracted from the zinc sulfate solution by 20% (v/v) di(2-ethylhexyl)phosphoric acid (D2EHPA) dissolved in kerosene at an initial pH of 0.5 and aqueous-to-organic phase ratio (A:O) of 6:1 using three countercurrent stages. Indium extraction is 96.1%, zinc and iron are barely extracted, and the separation factors of indium with respect to zinc and iron are 3640 and 4809, respectively. The complete stripping of indium from the loaded organic phase is achieved using 4 mol/L HCl at an A:O of 1:6. A scheme for direct solvent extraction of indium in zinc hydrometallurgical processing is suggested, by which indium can be concentrated into a small volume of strip solution containing 11 g/L of indium, which is 85 times its concentration in the feed solution. [ABSTRACT FROM AUTHOR]

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 Fe 2 + /Fe 3 + 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 H 2 SO 4 , 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 Fe 2 + /Fe 3 + 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 Fe 3 + into Fe 2 + at the same time. [ABSTRACT FROM AUTHOR]

Solvent extraction and separation of indium and copper from zinc residue reductive leach liquor containing a high concentration of zinc (ca. 85 g/L) and iron (ca. 35 g/L) was studied. Di-(2-ethylhexyl) phosphoric acid (D2EHPA) and Acorga M5640 were used as extractants for indium and copper, respectively. Indium was preferentially extracted by 15%(v/v) D2EHPA with three-stage extraction using an aqueous/organic (A/O) phase ratio of 6/1. Indium was effectively stripped from the D2EHPA organic phase by 4 M HCl. Copper was subsequently extracted selectively from the indium-extracted solution using 15%(v/v) Acorga M5640 with three-stage extraction using an A/O phase ratio of 2/1. Copper in the loaded Acorga M5640 organic phase was stripped by a synthetic spent electrolyte solution containing 25 g/L Cu and 180 g/L H 2 SO 4 . Based on the experimental results, a flowsheet for the separation and recovery of indium and copper from the reductive leach solution was developed and tested. The results showed that 95.4% of indium and 95.5% of copper were extracted, and the measured separation factors β In/Zn , β In/Cu , β In/Fe , β CuZn , and β CuFe were 4979, 1975, 3719, 1719, and 2446, respectively. [ABSTRACT FROM AUTHOR]