The Cathodic Behavior of Silver Ions During the Electrorefining of Copper
Silver is the most difficult non-copper impurity element to be purified and removed during the preparation of high-purity copper products by electrolysis. This is primarily due to the unpredictable behavior of trace amounts of silver during electrolysis. As a result, current methods for reducing silver content in cathode copper are limited and often ineffective, with silver levels remaining above 8 ppm. This work examines the cathodic behavior of Ag + during copper electrolysis using thermodynamic and kinetic theoretical calculations, variable experiments, and a detailed analysis of the trace Ag phase in copper cathode. Experimental findings indicate that the concentration of Ag + in the electrolyte is the primary determinant of silver content in cathode copper, specifically, the silver content in copper cathode rises dramatically with increasing the concentration of Ag + in the electrolyte. Under the condition of current density 300 A/m 2 , T = 63 °C, Ag + concentration of 0.01 mg L −1 , the silver content in copper cathode diminishes by 81.43 pct from 8.51 to 1.41 ppm. Combining electrochemical tests (cyclic voltammetry and square wave voltammetry) with scanning electron microscopy, an intriguing revelation has emerged. Following electromigration, diffusion, desolvation, and electroreduction, the silver most likely embeds into the copper deposition layer with the occurrence state of Cu 9 Ag solid solution alloy, rather than the traditional belief that silver exists as an independent silver element. This study contributes to a fundamental understanding of the underlying causes of the difficulty in removing silver from copper cathode, and provides inspiration for the development of new methods to improve the purity of electrolytic copper and to reduce the silver lost therein. Graphical
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