Preparation of high-purity copper by electrolytic refining in nitric acid system
High-purity copper has been widely used in semiconductor materials,optoelectronics and other fields due to its excellent physical and chemical properties such as ductility,thermal conductivity and electric conductivity.With the rapid development of electronic information industry,the copper product with high purity is pressing needed.Numerous methods such as zone melting,electron beam melting and electrolytic refining have been developed for the preparation of high-purity copper.Among these technologies,electrolytic refining has been investigated extensively and used in the industrial production for high-purity copper owing to its operation flexibility,simple-process and environmental-friendliness.In general,the electrolytic refining methods for the preparation of high-purity copper could be divided into nitric acid system and sulfuric acid system electrolytic refining.The electrolytic refining for high-purity copper preparation in sulfuric acid system has been widely used in industry.However,the high-purity copper prepared in sulfuric acid system generally contains the higher content of impurity elements such as S than in nitric acid system.Therefore,in this study,the 5N purity of copper was prepared from the raw materials of 4N copper in nitric acid system by one-step electrorefining.The effects of H2O2 addition,current density,electrolyte pH,Cu2+concentration during the electrorefining process were systematically studied.Under the optimum conditions of Cu2+concentration of 80 g/L,pH of 1.0,H2O2 addition of 0.10 mL/100 mL,and current density of 200 A/m2,the electrolytic product deposited on the cathode surface exhibited the smooth morphology,and the current efficiency during the electrorefining process was over 97％.Furthermore,the impurity elements including S,Ni,Se,As,Sb,Pb,Bi in the electrolytic product were detected by ICP-MS.The results showed that the purity of the copper prepared under the optimum conditions reached the 5N grade,which was consistent with the national standard of 5N high-purity copper.
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