Influence of deposit morphology on the kinetics of copper cementation on pure iron

Abstract

The kinetics of copper cementation on pure iron substrates were studied using a rotating disc geometry. The effect of rotational speed of the iron disc, copper ion concentration, hydrogen ion concentration, and temperature on the kinetic response was investigated. The range of each parameter studied was selected with some consideration for commercial operations for copper recovery using iron as the precipitant metal. The optimum values of each parameter for maximum cementation rate were determined. At low temperatures (10–30°C), an experimental activation energy of 22.89 kcal mol −1 was calculated indicating that the system is strongly controlled by a surface reaction mechanism or pore diffusion process. At high temperatures (30–60°C), an experimental activation energy of 7.94 kcal mol −1 was obtained which shows that the system may be controlled by both diffusion and surface reaction mechanisms. The deposits obtained were pure copper and not a copper-iron alloy. The total iron consumption, presented as can factor, was around 1.0. The structural characteristics of the resultant deposits were studied with the help of a scanning electron microscope. The structure and morphology of the deposits were analyzed in conjunction with their respective specific rate constants. A change in the surface roughness of the rotating disc and hence in the effective deposition surface area as a result of modification to the deposit morphology obtained for different experimental conditions was found to be the major reason for variations in the reaction rate. For the experimental conditions employed in this study, most of the deposits seen were bulbous or botryoidal crystal masses of different degrees of texture and size.