KINETICS OF ZINC REMOVAL FROM COBALT ELECTROLYTES BY ION EXCHANGE

Abstract

The removal of trace zinc concentrations from the INCO (Port Colborne) cobalt advance electrolyte by solvent impregnated ion exchange was studied in column and batch tests. The resins OC 1026, SIR 272 and SIR 302 were compared in terms of zinc loading and selectivity. The OC 1026 resin demonstrated superior zinc loading and selectivity characteristics, but retained significant amounts of cobalt. Cobalt loading was determined to be closely related to the electrolyte pHdrop across the column. Resin pre-treatment with the advance electrolyte at pH 3 acts to diminish the pH drop across the column, and hence reduced the cobalt retained. Results from batch tests were fitted to kinetic models to gain an insight into process mechanisms. It was found that pre-treatment enhanced the apparent diffusion coefficient inside the resin phase by nearly an order of magnitude, improved exchange kinetics by allowing a lower pH reduction during the loading process, and improved Co²⁺/Zn²⁺ exchange in a matrix of the cobalt complex. Breakthrough curve analysis was also undertaken to determine the rate determining steps in the column process. Further work is needed in X-ray microprobe analysis of resin samples from various portions of the column after loading, to gain a better understanding of the column loading process. The use of zinc selective electrodes in batch tests could also be undertaken to obtain more accurate estimates of diffusion and mass transfer coefficients.