Influence of Zn2+ ions on copper electrowinning from sulfate electrolytes

During electrowinning of copper from wastes, it was observed that Zn2+ impurities had some effects on the aspect of the deposits although the codeposition of these two metals is impossible under normal conditions. Cyclic voltammetry, impedance analysis and rotating disc electrode techniques were used to characterize the effect of the presence of small amounts of Zn2+ on the copper electrodeposition kinetics from acidic sulphate electrolytes. SEM and X-ray diffraction analysis were used to determine the morphology and the structure of the copper deposits. Their composition was determined using X-ray dispersive analysis. The addition of small amounts of Zn2+ had no effect, either on the crystal growth orientation of the copper deposits, or on their composition, but it modified slightly their morphology by increasing their microscopic roughness. An increase in the cathodic peak of the cyclic voltammograms observed in the presence of Zn2+ can be attributed to the higher roughness of the copper deposits. From impedance analysis, it can be deduced that Zn2+ ions are electrosorbed at the interface and have an effect on the copper electrodeposition kinetics. The adsorption capacitance, Ca, was calculated and correlated with the Zn2+ concentration. It was found that the nucleation time constant, parameter influenced by the growing mode of the deposit, decreased in the presence of Zn2+, especially at low concentrations.