Electrochemistry of conventional gold cyanidation

The kinetics of conventional gold cyanidation in air has been studied using open circuit potential measurements, voltammetry and atomic absorption spe ctrophotometry. The experimental results show that this is a complex proces s characterized by the interdependency of the different variables (cyanide concentration, pH, temperature and stirring speed). The measurement of the mixed potentials at which the process takes place gives valuable informatio n to ascertain the influence of each variable. A good correlation between m ixed potential and dissolution rate, thus having a potential interest for a n industrial application, has been found. The study of the current-potentia l curves for oxygen reduction on gold surface and anodic dissolution of gol d in cyanide solutions gives more insight into the control of the process: depending on the experimental conditions, gold dissolution takes place in t he active region (oxygen diffusion control) or in the potential region wher e dissolution of adsorbed species limits the rate of the process. Depending also on the experimental conditions, two or four electrons are transferred per oxygen molecule. (C) 1999 Elsevier Science Ltd. All rights reserved.