Behaviour of copper anodes containing oxygen, silver and selenium impurities during electro-refining

Abstract

The anodic passivation of copper anodes containing oxygen, silver and/or selenium as impurities has been investigated in sulphuric acid at 65.0±0.2 °C by voltammetric, chronopotentiometric and impedance techniques. A stationary electrode was used at a slow potential scan rate for the voltammetric technique. The voltammograms of the pure copper and alloy copper anodes exhibit three characteristic regions : the active dissolution, region I, the dissolution and precipitation, region II, and a current plateau passivation, region III. Electrochemical results obtained in this study show that passivation of copper anodes increases when impurities are added in the following order : Cu → Cu-O → Cu-Ag → Cu-Se → Cu-Ag-Se. X-ray diffraction results show that the anode surfaces, in the passive region, were covered by copper powder, silver and selenides.