Chlorine inclusion mechanism in high purity copper electrorefining from nitric acid system
(College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China)
Abstract: A practical approach was introduced to study the inclusion mechanism of chlorine in high purity copper electrorefining from nitric acid system via cyclic voltammetry (CV) combined with electrodeposition experiments. The CV curves display an obvious reduction peak of CuCl intermediate, which can provide an insight into the electrochemical behavior of this inclusion. Experimental results show that the increase of HNO3 concentration is favorable to reducing the quantity of chlorine inclusion although there is a slight decline in cathodic current efficiency. The optimum conditions for copper electrorefining in nitric acid system are HNO3 concentration in solution of 1-2 mol/L, moderate temperature of ~35 °C with current density not exceeding 25 mA/cm2. Based on the theoretical studies, an optimized copper electrorefining experiment was designed to simulate the industrial electrolysis, by which high purity copper can be obtained with chlorine inclusion less than 10 μg/g and current efficiency higher than 90%.
Key words: copper electrorefining; nitric acid system; cuprous chlorine; inclusion mechanism