The oxidation of manganese ions on lead alloys during the electrowinning of copper
Manganese ions are often encountered as impurities in the electrolyte used in the electrowinning of copper. The effects of manganese ions in the electrolyte on the anodic behaviour of lead-calcium-tin anodes used in the electrowinning of copper have not previously been definitively established. Potentiostatic oxidation of rotating disc electrodes of Pb-Ca-Sn anodes has been used to investigate the anodic behaviour of these anodes and the oxidation reactions of manganese ions in sulphuric acid solutions. The electrochemical measurements were complemented by chemical analyses of the oxidized manganese species formed during the anodisation process.
The oxidation of manganese on these anodes was found to occur at potentials above about 1.7 V and is also accompanied by oxidation of the lead and evolution of oxygen at potentials above about 2.0 V. The amount of manganese oxidized increases with increasing oxidation potential.
The presence of manganese in the electrolyte decreases the rate of formation of lead dioxide and reduces the fraction of the charge associated with oxygen evolution. Higher concentrations of manganese(m and lower oxidation potentials favour the production of manganese (III) which can form a MnOOH intermediate layer, while permanganate is produced at low concentrations of manganese(II). Mn02 powder produced by chemical precipitation reactions involving manganese (III) and permanganate(VII) ions, was also formed in the bulk electrolyte and on the walls of the cell.
Mechanisms for the various reactions are presented together with recommendations for minimization of permanganate formation in copper tankhouse electrolytes.
|Publication Type:||Conference Paper|
|Murdoch Affiliation:||Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions|
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