Kinetic aspects of galvanic interactions between minerals during dissolution

Abstract

A quantitative description of galvanic interactions between sulphide minerals based on thermodynamic and kinetic parameters has been developed. A voltage balance over the galvanic couple provides the basis for a mathematical description of the magnitude of the galvanic interaction. The contributions to the voltage balance include the cell emf of the galvanic couple, kinetic descriptions of the anodic and cathodic half-reactions, the voltage characteristics of mineral-mineral contacts and the voltage losses across the solution. The rates of the anodic and cathodic half-reactions were modelled by the Butler-Volmer equation and the diffusion equation. The galvanic couples were constructed as rotating ring-disc electrodes so that solution voltage losses were negligible. Two galvanic couples, copper-pyrite and galena-pyrite, were characterised by initially determining the thermodynamic and kinetic parameters associated with the anodic and cathodic half-reactions under different conditions of ferric concentration, electrode rotation rate and temperature. A potentiostat was used to vary the voltages losses across mineral-mineral contacts. The effect that semiconducting properties of minerals have on the magnitude of the galvanic interaction was described by examining the anodic dissolution of galena under illumination. The thermodynamic and kinetic parameters were used in the mathematical model to obtain a prediction of the magnitude of the galvanic interaction. The mathematical model is observed to be in good agreement with the experimentally measured galvanic currents.