Study of the kinetics of silver ions cementation onto copper from sulphuric acid solution

Abstract

The kinetics of silver cementation with copper from sulphuric acid solution has been studied with a rotating cylinder. Two independent methods have been used to monitor the concentration of Ag + ions in the solution: atomic absorption spectrophotometry (AAS) method and a continuous method with the use of an ion-selective electrode. The reaction has been found to follow first-order kinetics with respect to silver ion concentration. The initial rate of the reaction is limited by diffusion through the mass transfer boundary layer. The rate constant for initial period of cementation is independent of the absence or the presence of oxygen in the solutions and is independent of the presence of Cu 2+ ions up to the concentration of 2×10 −4 M. After the initial period of cementation a rate enhancement has been observed. In solutions containing 20 mg/L of Ag + ions, the rate enhancement is associated with changes in the structure of the deposit which involve an increase in the effective surface area during the process. However, the rate enhancement phenomenon in the absence of oxygen at 100 mg/L of Ag + is attributed not only to an increase in the effective surface area but also to a chemical reaction between Cu + and Ag + ions.