Study of the kinetics of the cementation of silver ions onto copper in a rotating cylinder system from acidic sulphate solutions

Abstract

The kinetics of the cementation of silver ions onto copper from acidic sulphate solutions were investigated in a rotating cylinder system. The influence of several parameters on the course of the reaction, such as cylinder rotation speed, initial concentration of silver ions, temperature, concentration of sulphuric acid and the presence or absence of oxygen in the system, was investigated, and the reaction was found to follow first-order kinetics. The initial rate of the reaction is limited by diffusion through the mass transfer boundary layer. The experimental values of the initial rate constant calculated from both methods used for recording the changes of the silver ions concentration in the solutions corresponded ideally to the values predicted by semi-theoretical equations describing the turbulent flow in the rotating cylinder system. After the initial period of cementation, an enhancement of the rate was observed. In oxygenated solutions, rate enhancement is associated mainly with changes in the structure of the deposit involving an increase in the effective surface area during the process. However, the rate enhancement phenomenon in the absence of oxygen is attributed not only to an increase in the effective surface area but also to the chemical reaction between the Cu + and Ag + ions.