Gold cyanidation using hydrogen peroxide

Gold cyanidation, using hydrogen peroxide as an oxidising agent, has been studied by performing kinetic experiments, open circuit potential measurements and voltammetry. Small amounts of hydrogen peroxide make the cyanidation rate lower than that in conventional cyanidation, but higher amounts can make the cyanidation rate double. At low temperatures, the process is controlled by a chemical reaction, whereas at higher temperatures, it is controlled by diffusion with higher rates with respect to conventional gold cyanidation at atmospheric pressure. As the presence of hydrogen peroxide displaces the mixed potential of cyanidation to more anodic potentials, where oxygen activity is nil, cyanidation can be performed under conditions of low oxygen pressure. In these conditions, cyanidation is established at transpassive potential regions of gold anodic dissolution and the cyanidation rate is determined by the cyanide concentration. The cyanidation rate can be tripled by adding small amounts of thallium (I) ions to cyanidation with hydrogen peroxide. (C) 1999 Elsevier Science B.V. All rights reserved.