Electrodissolution Kinetics of Copper in Acidic Chloride Solutions

Abstract

The anodic dissolution of copper in acidic chloride media was studied at arotating disk electrode by the linear potential sweep method. The potentialrange from the rest potential to +400 mV vs. SCE, including a limiting currentregion, was investigated. Twenty different solutions of various chloride ionconcentrations from 0.2 to 4M and various [K+] to [H+] ratios were tested.The observed anodic limiting current density was proportional to the squareroot of the rotation rate. A model, which assumes the formation of a CuClfilm on the copper surface and diffusion of the chloride ions to the electrodeas the rate-determining step, has been developed to interpret the experimentaldata. Complexation constants, K2 and K3 are calculated as 6.67 � 104 and1.81 � 105, respectively, and K3/K2 = 2.67. These results lead to the conclusionthat in solutions with [Cl-] < 0.7M the complex, CuCl2-, is dominant, whileat more concentrated chloride solutions, CuCl32- is the main complex formed.For [Cl-] < 0.05M, a considerable amount of the dissolved copper is in theform of Cu2+. This restricts the proposed mechanism for anodic dissolutionof copper to solutions of higher chloride concentrations. The calculations donot preclude the validity of a previously proposed mechanism which suggeststhat diffusion of the cuprous chloride complex to the bulk of the solution isthe rate-determining step.