Effect of lead and oxygen on the passivation of copper anodes

The effect of lead and oxygen upon the passivation of copper anodes during electrorefining was investigated in sulfuric acid at 65.0+/-0.2 degrees C b y electrochemical methods and by surface analysis. CuO was present in the c opper matrix. It was generated through oxidation of Cu2O present during hea l treatment. It was found that CuO accelerates the dissolution of the anode . The voltammetric technique showed that a higher quantity of lead increase s the passivation of copper. When both lead and oxygen were present, less p assivation was observed. Voltammetric reduction of the passive layer showed the presence of CuO, Cu2O and lead compounds. Surface analysis confirmed t he presence of CuO and Cu2O in the passive layer. Finally, the impedance re sults have demonstrated that a three step mechanism with two adsorbed speci es can be employed to explain this passivation reaction. (C) 1999 Canadian Institute of Mining and Metallurgy Published by Elsevier Science Ltd. All r ights reserved.