Influence of Co2+ ions on cathode behaviour during zinc electrowinning

The effect of Co2+ ions on zinc deposition from acidic sulfate electrolytes is investigated on the basis of steady-state polarization curves and imped ance measurements. Hydrogen evolution is shown to be enhanced by adsorbed c obalt on both the zinc deposit and the aluminium substrate, and this stimul ation occurs in combination with the catalytic effect of adsorbed species o riginating from anodic products. Hydrogen evolution involves a diffusion-co ntrolled step and a slow adsorption process which is the rate-determining s tep. It also induces the redissolution of the zinc deposit observable from the potential dependencies of current, charge transfer resistance and doubl e layer capacitance.