BEHAVIOUR OF COPPER ANODES CONTAINING OXYGEN, SILVER AND SELENIUM IMPURITIES DURING ELECTRO-REFINING

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 using voltammetric, chronopotentiometric, and impedance techniques. A stationary electrode was employed at a slow potential scan rate during the voltammetric measurements. The voltammograms of both pure copper and alloy copper anodes exhibited three characteristic regions: active dissolution (region I), dissolution and precipitation (region II), and a current plateau indicating passivation (region III). Electrochemical results revealed that the passivation of copper anodes increases with the addition of impurities, following the sequence: Cu + Cu-O + Cu-Ag + Cu-Se → Cu-Ag-Se. X-ray diffraction analysis demonstrated that the surfaces of the anodes in the passive region were covered with copper powder, silver, and selenides, depending on the alloy used. This study highlights the effects of specific impurities on the electrochemical behavior of copper anodes during the electro-refining process, contributing to the understanding of passivation mechanisms essential for improving refining efficiency.