Effect of Thallium Adatoms on Electrode Processes in the System Gold–Cyanide Solutions

Abstract

The possibility of determining kinetic parameters of the gold electrodeposition in the presence of thallium adatoms is considered. The coverage θ of the electrode surface by thallium adatoms is monitored. The steady-state values of potential used correspond to current densities i that are directly proportional to the concentration of thallium ions in solution. The procedure is based on the assumption that the rate of incorporation of adatoms is proportional to the product iθ. With θ increasing to ∼0.25, the exchange current and transfer coefficient increase from 5 × 10^–5 A cm^–2 and 0.23 in pure solutions to1.5 × 10^–4 A cm² and 0.6 at θ = 0.25–0.3, whereas the reaction order by cyanide ions remains practically invariant with increasing θ. Variations in the kinetic parameters with θ are compared to similar measurements obtained earlier for the anodic process. These may be made consistent by assuming that mechanisms of cathodic and anodic reactions differ in pure solutions and are identical in the presence of catalytically active adatoms. An explanation to the above regularities is given.