Modified zinc sulphate solution purification technique to obtain low levels of cobalt for the zinc electrowinning process

Abstract

Zinc sulphate solution purification is very critical in the conventional `roast–leach–electrowin' process when adopting the hydrometallurgical route for the production of zinc metal. Various purification methods are used in practice to achieve high quality neutral zinc sulphate electrolyte with minimum levels of impurities. A modified single-stage zinc sulphate solution purification process is described in this paper with an aim to bring down cobalt to low levels. It involves a single-stage purification with two-stage operation using potassium antimony tartrate (PAT), copper sulphate and zinc dust for the removal of impurities. The results obtained at both laboratory scale and plant scale and the optimum parameters to achieve the high quality solution are described. Chemical kinetics, copper requirement, zinc dust dosage and temperature for the removal of impurities and the composition of the final purified zinc sulphate solution obtained are discussed. The paper also compares the existing operating performance of the plant and the results obtained through this modified solution purification technique. This suggested new process is very simple and provides an improved electrolyte for the down-stream electrowinning operation.