Development of a stable MnO₂Protective layer on lead-based electrowinning anodes

Corrosion resistance of the lead-based anodes directly influences the purity of the final product in the zinc electrowinning process. The anodic MnO₂ layer that is electrodeposited on the anodes during this process can protect the anodes against corrosion. Sand-blasted anodes generate a uniform, adherent and shiny MnO₂ layer, which gradually blisters and eventually sloughs off after several weeks. In this study, we attempted to develop a new method to stabilize the MnO₂ protective layer on the anodes during the electrowinning process by providing suitable nucleation sites for electrodeposition of this layer. MnO₂ particles (P₈₀=40µm) were used as seed material for this purpose. Different techniques of galvanostatic and cyclic voltammetry polarizations, scanning electron microscopy (SEM) and atomic absorption spectroscopy (AAS) were employed to investigate the performances of the MnO₂-seeded lead anodes. The experimental results showed that growth of the MnO₂ layer is influenced by the MnO₂ seed particles on the anode surface. The MnO₂ layers electrodeposited on the MnO₂-seeded lead anodes were uniform and strongly adherent to the substrate. This layer was more stable than those formed on the PbAg anode without MnO₂ seeding. This could provide the anode with a higher level of corrosion protection. Moreover, formation of undesirable MnO₂ mud in the electrolyte and the rate of manganese consumption were decreased when the MnO₂-seeded lead anodes were polarized. These observations could be attributed to the different properties of the electrodeposited MnO₂ layer on this anode in comparison with that formed on the PbAg anode.