Direct solvent extraction of indium from a zinc residue reductive leach solution by D2EHPA

• A direct solvent extraction method was employed for the extraction of indium.
• 96.1% indium was extracted by three countercurrent stages of extracion.
• Indium enrichment in the stripped solution was 85 times as compared to the feed.
• Flow sheet for extraction indium from the zinc hydrometallurgy process was proposed.

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.

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