THE ROLE OF CATHODE MACROMORPHOLOGY IN ZINC ELECTROWINNING CURRENT EFFICIENCY

The impact of cathode macromorphology or surface roughness on zinc current efficiency at various temperatures (35-45-degrees-C), sulfuric acid (150-250 g l-1), antimony (up to 0.06 mg l-1), nickel (up to 30 mg l-1) and glue concentrations (up to 20 mg l-1) was evaluated. The results have shown that surface roughness is particularly influential when the electrolyte contains impurities such as nickel and antimony. Current efficiency does not change substantially with surface roughness if the electrolyte is sufficiently pure. Smoother zinc cathodes tend to retain a more favorable macromorphology, and are less sensitive to the impurities. Glue helps to counteract the effect of the impurities; however, in some instances it increases surface roughness and a decrease in current efficiency can result. A definite correlation was observed between the data obtained by cyclic voltammetry and the current efficiency tests. The experimental results indicate that surface morphology could be a significant variable in relating the induction period or the onset of diminishing current efficiency with the impurity concentration of the zinc electrolyte.