Reductive leaching of indium from zinc-leached residue using galena as reductant

Abstract Large quantities of indium-bearing zinc-leached residue (ZLR) are produced constantly in the hydrometallurgical production of zinc, including zinc, indium, iron and other valuable metals. In order to recover valuable metals from the residue, a new reductive leaching process using galena as reductant has been developed, in which the extensive leaching of zinc and indium is achieved. A shrinking core model under the control of surface chemical reaction best fitted the leaching of indium from the residue. The apparent activation energy of indium leaching was calculated to be 64 kJ/mol, and the reaction orders were determined as −0.34 and 1.47 with respect to particle size and initial H2SO4 concentration, respectively. The extent of leaching was 87% for zinc, 91% for iron and 88% for indium after 90 min at 85 °C, using an initial H2SO4 concentration of 140 g/L and a molar ratio of lead sulfide to zinc ferrite of 1:1. The reductive leaching process of the residue achieved high dissolution of zinc and indium, and iron existed as Fe2+ in solution would prove beneficial for the subsequent iron removal stage.