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A study of the kinetics of the anodic oxidation of chloride ions on the surface of lead-silver anodes used for the electrowinning of zinc has shown some interesting and practically important results. Oxidation of chloride does not occur on a PbSO 4 surface but occurs readily on a PbO 2 surface. Oxidation of chloride occurs at the mass-transport controlled rate at the operating potentials of anodes during the electrowinning of zinc in the absence of manganese in the electrolyte. However, the rate of oxidation of chloride ions is significantly lower in the presence of manganese ions in the concentration range 1 to 5 g/L. These results have been compared with plant observations that confirm the lower rate of chlorine generation in the presence of manganese. The use of periodic current reversal does not increase the rate of oxidation of chloride ions in the presence of manganese ions. The rate of anodic oxidation of chloride in the presence of manganese ions is too low to be of practical value in controlling the chloride levels during the electrowinning of zinc. [ABSTRACT FROM AUTHOR]

A review of the literature dealing with the effect of cobalt on lead-based anodes for oxygen evolution during electrolysis of sulfuric acid solutions verifies that the presence of cobalt at the anode-electrolyte interface, either as constituent of the anode material or as ions in the electrolyte, catalyzes the evolution of oxygen and reduces the corrosion of the anodes and the contamination by lead of metal cathodes produced during electrowinning. However, due to harmful effects of cobalt ions on the cathodic reaction in some processes, these benefits are limited to the electrowinning of copper. Efforts to develop a way of introducing cobalt at the anode-electrolyte interface without interfering with the cathodic reactions are reviewed in this paper. The use of lead-cobalt alloy anodes has had limited success due to issues arising from the low solubility of cobalt in lead, segregation during casting of the alloys, and nonuniform distribution of cobalt which affects the integrity of the anodes. This has been overcome in part lately by inclusion of cobalt into only the surface layer of a lead or lead alloy substrate, by thermal treatment of a cobalt salt to form a catalytic cobalt oxide surface species, or by electrodeposition of composite lead-cobalt oxide anodes. The last approach in particular has been actively investigated by several groups, but to our knowledge it is yet to find application in the industry. The review also critically examines the likely reaction mechanisms involved. [ABSTRACT FROM AUTHOR]

The effect of cobalt ions in the electrolyte on the performance of lead alloy anodes used for oxygen evolution during electrolysis of copper/sulfuric acid solutions has been studied extensively over the past 90 years. A review of the literature has confirmed that cobalt both as constituent of the anode material and present as ions in the electrolyte reduces the rate of corrosion of the anodes, lowers the overpotential for the evolution of oxygen, and reduces lead contamination of the copper cathodes. Despite the fact that these effects have been developed into widespread applications in the electrowinning industry, a fundamental understanding of the mechanism of the action of cobalt ions remains a point of debate. A selection of the most relevant literature on this phenomenon has been reviewed and the data and proposed mechanisms critically evaluated. [ABSTRACT FROM AUTHOR]