Lead Anodes Used for Zinc Electrowinning

Lead Anodes Used for Zinc Electrowinning

Zinc electrowinning is the electrodeposition of zinc ions on the cathode, oxygen evolution on the anode, as well as hydrogen evolution on the cathode as a side reaction. This process operates in highly acidic solutions and at high current densities. Conventional lead-based anodes used in zinc electrowinning are associated with high corrosion rates and oxygen evolution overpotential in the electrowinning process. These result in some problems such as Pb contaminating the zinc cathode, shortened anode lifetime, and high energy consumption in the process.

Lead-based composite anodes have been introduced to address these issues by using electroactive oxide particles dispersed in the Pb anode. Manganese ions, which typically exist in the zinc electrowinning electrolyte, can influence the anode performance, depending on their concentration and the anode material.  
A combination of electrochemical and analytical methods was used to understand the oxidation, electrocatalytic activity, and corrosion performance of the Pb-MnO2 composite anodes compared to the conventional PbAg anode. Potentiometric titration was utilized to measure the oxidation rate of manganese ions. The anodic corrosion layers and the MnO2 deposited layers were characterized by Scanning Electron Microscopy and X-Ray Diffraction.
A new electrochemical method was also developed for an on-site investigation of the deposited MnO2 layer on the anodes.

The new lead anode (composite of Pb-MnO2) used for zinc electrowinning showed higher catalytic activity and better corrosion resistance than the PbAg anode under the zinc electrowinning operating conditions.The Pb–MnO2 anode can decrease the energy consumption in the electrowinning process in the Mn-free electrolyte by up to 5%. The composite particles were not effective in decreasing the anode potential in the Mn-containing electrolyte. The MnO2 particles catalyzed Mn(III) disproportionation, contributing to the deposition of a uniform, adherent, and protective MnO2layer. The formation of this layer decreased the lead dissolution and manganese consumption rates. The Pb-MnO2 composite anode can be put into service without any pre-treatment since it quickly develops a stable MnO2 layer and generates very low MnO2 mud.