Rate processes for silver and gold cyanidation are controlled by a series of coupled electrochemical reactions. These include anodic metal dissolution and oxygen reduction. This study demonstrates basic differences between silver and gold dissolution both in reference to the metal and the accompanying oxygen discharge. The kinetics of oxygen reduction are compared for silver and gold. At a fixed voltage, the cathodic current for gold is less than that of silver except at large negative potentials where the kinetics are oxygen diffusion-limited. A mathematical model is presented for oxygen reduction based upon two paths: one path with peroxide formation followed by alternate catalytic decomposition and desorption, and a second path with continued peroxide reduction to hydroxyl ions. The model permits separate calculations of the first and second waves of oxygen reduction. Based upon mixed potential models, silver dissolution is shown to be controlled by both the first and second waves of oxygen reduction with the number of electrons approaching four for high cyanide concentrations. Gold dissolution is controlled by surface reactions with mixed potentials associated mainly with the first wave of oxygen control and limited to two-electron transfer. The model permits an evaluation of the number of electrons which may be transferred for a given potential and shows this number is voltage-dependent. Silver dissolution is shown to include both diffusion or mixed diffusion plus charge transfer kinetics, influenced by the degree of agitation and both oxygen and cyanide concentration-dependent. Gold dissolution kinetics are controlled by crystal-dissolution overpotentials and are independent of agitation, Models of oxygen discharge and metal dissolution are used to explain observed characteristics and kinetics of silver and gold leaching. (C) 2000 Elsevier Science B.V. All rights reserved.