Effect of Solution Composition on the Passivation of Anode in Copper Electrorefining

Abstract

To elucidate the effect of solution composition on the passivation of anode in Cu electrorefining, the potentiodynamic polarization curves were measured by polarizing from -0.2 V versus NHE to 1.0 V using the potential sweep method at 1.0 mV·s−1. The diffusion coefficient was measured by rotating disc electrode method under the conditions of 50, 100, 150, 200, 250 and 300 revolutions per minute of disc electrode and polarizing from 0.34 V to -0.40 V at 10.0 mV·s−1. The critical current density for passivation and the passive current density decreased linearly with total concentration of SO4 in solution regardless of solution composition and the presence of impurities such as As3+，Sb3+ and Bi3+, showing the good correlation between the current density for passivation and the total concentration of SO4. The diffusion coefficient of Cu2+ ions decreased with total concentration of SO4 in solution. The increase in passivation with the total concentration of SO4 is attributed to both decreases in solubility of CuSO4 in electrolyte and the diffusion coefficient of Cu2+ ions. On the other hand, focusing on the effect of kinds of cation on the passivation, the harmful effect on the passivation was largest with Cu2+ ions, and was larger in the order with Li+，Ni2+ and Na+ ions, and was smallest with H+ ions. The diffusion coefficient of Cu2+ ions decreased most with Ni2+ ions, and decreased secondly with Li+ and Na+, and decreased least with H+ ions. The diffusion coefficient of Cu2+ ions decreased with increasing the viscosity of solution.

Keywords

• passivation
• slime
• copper
• anode
• electrolysis
• passive state