Oxygen evolution and corrosion behaviors of co-deposited Pb/Pb-MnO2 composite anode for electrowinning of nonferrous metals

The oxygen evolution and corrosion behaviors of Pb/Pb-MnO2 composite anode in H2SO4 solution were investigated comparing with Pb and industrial Pb-Ag (1.0%) anodes. Its electrocatalytic activity towards oxygen evolution reaction (OER) and corrosion resistance were evaluated using galvanostatic polarization and ionic equilibrium method. The microcosmic morphology of the anodic layer during the polarization was observed using Scanning Electron Microscope (SEM). The results indicate that this kind of composite anode displays particular anodic behaviors during the galvanostatic polarization due to the changes of surface state: A potential valley with the minimal potential of about 300 mV lower than that of Pb anode can be observed at the very beginning of the polarization; then the anodic potential gradually decrease. The stable potential after 72 h is 100-150 mV lower than that of Pb anode and comparable to industrial Pb-Ag (1.0%) anode. Furthermore, the corrosion resistance of the composite anode largely depends on the MnO2 content in deposit. The dissolution of Pb is very little at the early stage, then, after standing a period of heavy intergranular corrosion, a stationary PbO2-MnO2 composite layer will be formed on the anode surface, which is predicted to present satisfactory corrosion resistance in the long-time electrolysis. (C) 2011 Elsevier B.V. All rights reserved.