Anodic behavior and microstructure of Al/Pb–Ag anode during zinc electrowinning

Abstract

Anodic behaviors and oxygen evolution kinetics of Pb–0.8%Ag and Al/Pb–0.8%Ag anodes during the initial 24 h zinc electrowinning were investigated with cyclic voltammetry (CV) curves and electrochemical impedance spectroscopy (EIS). The results reveal that the anodic behaviors and reaction kinetics of the two anodes vary a lot during the anodic polarization which indicate the formation and stabilization of anodic layer. Compared with conventional Pb–0.8%Ag anode, Al/Pb–0.8%Ag anode has longer time of anodic polarization. At the very beginning of anodic polarization, the two anodes all exhibit higher potential of oxygen evolution reaction (OER) since the reaction is controlled by the transformation step of intermediates. Then, its OER potential is largely diminished and OER rate is deduced from the formation and adsorption of the first intermediate (S–OHads). In the prolonged anodic polarization, the anodic potential of Al/Pb–0.8%Ag gradually decreases and the final value is more stable than that of conventional Pb–0.8%Ag anode. On the anodic layer after 24 h of anodic polarization, the OER potential is controlled by the formation and adsorption of intermediate. The microstructures of Al/Pb–0.8%Ag and Pb–0.8%Ag anodes after 24 h of anodic polarization were analyzed by scanning electron microscope (SEM).