The corrosion of silver and silver sulphide in halide solutions in water and dimethylsulphoxide

Abstract

A kinetic study has been made of the dissolution of silver and its sulphide, mainly by Fe(III) and Cu(II), in halide solutions in dimethylsulphoxide (DMSO) and water. In aqueous solution the corrosion of silver is complicated by surface film formation: the reaction is slow and the recovery less than 70%, even when Cl 2 is used as the oxidant. In DMSO, because of the stronger halide complexing and the higher solubility of AgCl, the dissolution of silver is both rapid and total, being complete within a few minutes. A detailed study of the aqueous reaction using a rotating silver disc indicated that the reaction rate is generally determined by solid state diffusion processes and follows parabolic kinetics. However, it is shown that solution diffusion control can also occur when the surface film is very thin or at low oxidant concentrations. These observations are shown to be consistent with previous literature studies. Silver sulphide was found to leach more slowly in DMSO solutions than in the corresponding aqueous media at 25°C, but the recovery was considerably higher under the conditions used in the present work.