Evaluation of Lead Anode Reactions in Acid Sulfate Electrolytes : II. Manganese Reactions

Abstract

Lead alloys containing calcium-tin, silver, or similar combinations are the primary insoluble anodes used for copper and zinc electrowinning. One potential concern with these anodes is the detrimental effect on cathode purity from incorporation of lead corrosion products. Other factors which are important to process economics are the reaction potential and overpotential required for oxygen evolution. In addition to the inherent overpotential, impurities in the electrolyte can have a significant polarization impact, such as the films that may form when manganese is present. In order to gain a better understanding of the fundamental behavior of various concentrations of manganese ions at lead anodes, the polarization behavior of lead calcium-tin and lead-silver alloys in sulfuric acid was evaluated. A common depolarizing agent, Co(II), was also used in some cases to determine possible interactions with manganese. The data show that manganese ions are active on the lead anodes and may precipitate manganese oxide in addition to electrochemical deposition. One possible precipitation mechanism seems to occur by the disproportionation of Mn(III). Co(II) lowers the electrode potential at given current densities which decreases Pb corrosion but favors formation. © 2002 The Electrochemical Society. All rights reserved.