Activation Energies of Anodic Gold Reactions in Aqueous Alkaline Cyanide

Abstract

The kinetics of the anodic reactions of gold in aqueous alkaline cyanide in the potential range −0.81 to +0.64V were studied by means of potentiostatic and potentiodynamic measurements for the temperature range 0°–50°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 kinetic behavior of the gold reaction in each of these regions was found to behave in the manner predicted by the single reaction mechanismThe dissolution reaction in the most cathodic of the three regions (−0.56 to −0.26V) was characterized by a high apparent activation energy and a lack of dependence on mass transfer. The second step in the reaction mechanism was identified as the rate‐determining step. The gold dissolution reaction in the intermediate potential region −0.26 to +0.39V was found to have a relatively high apparent activation energy (47–55 kJ/mol) 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 +0.64V), the gold dissolution reaction was found to be under diffusion control with an apparent activation energy of 16–18 kJ/mol. The third step in the reaction mechanism was identified as the rate‐determining step. A fourth region (−0.81 to −0.56V) observed in potentiodynamic measurements was found to have an apparent activation energy of with little dependence on mass transfer. The reaction was identified as an adsorption reaction.