Lead Alloy Anodes Used in Zinc Electrowinning

Lead Alloy Anodes Used in Zinc Electrowinning

The zinc electrowinning process is usually performed at high current densities (450-550 A/cm2), which can result in a high anode potential. Consequently, the anodes stability and the corrosion resistance in acidic solutions are also very important factors for the evaluation of the electrowinning anodes. These properties determine the service life of the anodes, the potential of the cells during the process, and the purity of the metal deposited on the cathode.

The lead anode in zinc electrowinning is most commonly used due to its low solubility in the solutions containing sulfuric acid, relative low cost, low melting point, and the high conductivity in both metallic and the highest oxidized states (PbO2). However, the OER overpotential on these anodes is high and their degradation resistance is relatively low.

Manganese ions usually exist in the zinc electrowinning electrolyte, which either originate from the ores or are added intentionally. These ions are oxidized to form an MnO2 oxide layer on the anode surface during the electrowinning process. This layer may improve the corrosion performance of the anodes and decrease lead contamination in the zinc product.

However, its protection performance strongly depends on the physical properties of the layer. Lead-based composite anodes are a new type of the electrowinning anodes that have been developed in order to address the problems associated with the conventional lead-based anodes. The composite anodes are composed of the active metal oxide particles dispersed in the lead or lead-dioxide matrices. The presence of the active particles can facilitate the oxygen evolution reaction and decrease the anode potential. The concerns in application of a new composite anode are the efficiency of the composite particles on promoting the oxygen evolution reaction, their effects on the electrowinning process and the deposition of the anodic MnO2 layer, and its durability and corrosion performance under the electrowinning operating conditions. Among all the options for the active composite particles, MnO2 is one of thestrongest candidates since it is catalytically active for OER and its dissolution does not negatively affect the zinc electrowinning process.