Recovery of cadmium from hydrometallurgical zinc smelter by selective leaching

A hydrometallurgical process for the recovery of cadmium was developed through a simple flowsheet of selective cadmium leaching from the Cd–Cu–Zn cake generated in electrolytic zinc circuit. The conventional route of cadmium leaching, sponging and re-leaching involves large number of stages and high capital expenditures. This research work relates to development of a simpler process approach for the recovery of cadmium in an electrolytic zinc circuit from the copper–cadmium cake of zinc purification section.The process consists of stages like zinc removal from copper–cadmium cake, selective cadmium leaching, and purification by removal of iron, thallium and cobalt followed by electrowinning and melting.The paper deals with zinc removal from copper–cadmium cake in two stages into the liquid phase with subsequent enrichment of copper and cadmium in cake.This cake was processed by selective cadmium leaching where a high solid–liquid ratio was maintained to attain higher cadmium concentration in the solution. The selective leaching of cadmium was performed under specific operating conditions so as to minimize co-dissolution of impurities into the cadmium rich solution.The reaction was terminated with start of copper dissolution. KMnO4 and NaOH were used to oxidize and precipitate the impurities like Tl, Fe and part of Co. Purified cadmium sulphate solution was fed for electrolysis and the cadmium cathode so obtained was melted to achieve cadmium metal quality of 99.95%. The overall cadmium recovery of this process flowsheet was found to be 70–72%. Based on the research work, a conceptual flowsheet was developed.