Influence of Zn2+ ions on copper electrowinning from sulfate electrolytes

During electrowinning of copper from wastes, it was observed that Zn2+ impu rities had some effects on the aspect of the deposits although the codeposi tion of these two metals is impossible under normal conditions. Cyclic volt ammetry, impedance analysis and rotating disc electrode techniques were use d to characterize the effect of the presence of small amounts of Zn2+ on th e copper electrodeposition kinetics from acidic sulphate electrolytes. SEM and X-ray diffraction analysis were used to determine the morphology and th e structure of the copper deposits. Their composition was determined using X-ray dispersive analysis. The addition of small amounts of Zn2+ had no eff ect, 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 cycli c voltammograms observed in the presence of Zn2+ can be attributed to the h igher roughness of the copper deposits. From impedance analysis, it can be deduced that Zn2+ ions are electrosorbed at the interface and have an effec t on the copper electrodeposition kinetics. The adsorption capacitance, Ca, was calculated and correlated with the Zn2+ concentration. It was found th at the nucleation time constant, parameter influenced by the growing mode o f the deposit, decreased in the presence of Zn2+, especially at low concent rations.