Validation and Implementation of Cold Purification Cake Leaching in Ammoniacal Carbonate Solutions at Hindustan Zinc Hydro Refineries

As a part of regular purification process for zinc leachate, cold purification cake is being generated at Hindustan Zinc refineries. Since the cake is being accumulated as an inventory, a treatment process has been designed to recover the copper in house and utilize it as an activator in zinc flotation circuit. It majorly contains copper (30-40%) along with zinc (10-20%) and cadmium (2%). With confirmation to the above statement, photomicrographs of purification cake also confirmed the major presence of copper in metallic or oxidized form. In present work ammoniacal carbonate leaching of purification cake followed by solvent extraction using diketone based solvent has been studied under the influence of various parameters viz., temperature, agitation, pulp density, ammonia, CO 2 dosages, solvent concentration, and impact of w/s zinc on leaching and solvent extraction. Leaching kinetics determined based on shrinking core model. Chemical reaction at unreacted core was found to be the rate controlling step. The estimated activation energy was found to be 24 KJ/mol. Leached copper has been extracted by solvent extraction with a β diketone based solvent and is stripped with sulfuric acid as concentrated copper sulfate solution. The above established R&D findings are successfully implemented in the Commercial plant with a treatment capacity of two tons of cold purification cake per batch.