Zinc recovery from zinc calcine by selective reduction roasting and acid leaching

Zinc recovery from zinc calcine containing high content of iron by selective reduction roasting and acid leaching was investigated. Zinc ferrite in zinc calcine was selectively transformed to zinc oxide and magnetite under CO and CO2 atmosphere. The reduced zinc calcine was then leached with sulfuric acid for dissolving the soluble zinc in the leaching solution and leaving the iron in the residue as magnetite. The effects of reaction parameters of reduction roasting and sulfuric acid leaching on the recovery of zinc were studied and the reduced sample was analyzed by chemical analysis, XRD and SEM-EDS. Using the content of soluble zinc and ferrous iron as the evaluation index of the reduction roasting, the optimum conditions were obtained as follows: roasting temperature (750?C), roasting time (60min), CO concentration (8%) and CO/(CO+CO2) ratio (20%). Under the optimum conditions, the content of soluble zinc in zinc calcine increased from 79.64% to 91.75%. With the leaching efficiency of zinc and iron as the evaluation index of the acid leaching, the best leaching conditions were obtained as follows: leaching temperature (normal temperature), leaching time (30min), sulfuric acid concentration (90g/L) and liquid to solid ratio (10:1). The leaching efficiency of zinc and iron under this condition is 91.8% and 7.17%, respectively.