Activation Energies of Anodic Gold Reactions in Aqueous Alkaline Cyanide

Abstract

The kinetics of the anodic reactions of Au in aqueous alkaline cyanide in the potential range --0.81 to +0.64 V were studied by means of potentiostatic and potentiodynamic measurements for the temp. range 0-50 deg C. The effects of mass transfer were also investigated. As in earlier works, three distinct regions of anodic activity (i.e. regions of anodic reactions) were found in potentiostatic measurements. The dissolution reactions in the most cathodic of the three regions (--0.56 to --0.26 V) was characterized by a high apparent activation energy (93 plus/minus 8 kJ/mole) and a lack of dependence on mass transfer. The second step in the reaction mechanism was identifed as the rate-determining step. The Au dissolution reaction in the intermediate potential region --0.26 to +0.39 V was found to have a relatively high apparent activation energy (47-55 kJ/mole) and a small dependence on the mass transfer. The second step in the reaction mechanism was identified as the rate-determining step. In the most anodic of the three regions (--0.39 to +0.64 V), the Au dissolution reaction was found to be under diffusion control with an apparent activation energy of 16-18 kJ/mole. 18 ref.--AA