Effect of thermal treatment of copper anodes on electrorefining process

Abstract

The aim of this paper is to study the effect of thermal treatment of the conventional copper anodes on the dissolution behavior and passivation of anodes during electrorefining process. Four similar impure copper anode samples were heated to 800°C with holding time of 1800s followed by quenching in different media to achieve different cooling rates such as brine 10%, water, machine oil and/or still air. Each anode sample was centered in an electrolytic cell together with two stainless steel permanent cathode sheets and all was immersed in an acidified electrolyte containing 0.040kg/l of Cu2+ and 0.170kg/l of H2SO4 with some bath organic additives like bone glue and thiourea. The process was carried out at a constant electrolyte temperature of 65°C, an electrolyte stirring rate of 350rpm and a constant cathodic current density of 350A/m2. Polarization curves for the different copper anodes using a potentiodynamic technique with a scanning rate of 0.5mV/s were conducted to examine the dissolution rate and passivation of different anodes. The obtained results indicated that, the best anodic dissolution rate and anodic passivation time are obtained with anodes quenched in water (2.685∗10−6kg/s & 450s), while that of untreated anode is only 2.023∗10−6kg/s and 348s. Thermal treatment of copper anodes has a good effect on the specific energy required for the electrorefining process where it is about 0.329kWh/kg when quenched anode in water is electrolyzed, while it is about 0.491kWh/kg when untreated anode was electrorefined.