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Thermodynamics and kinetics of the dissolution of gold under pressure oxidation conditions in the presence of chloride

Liu, J.Q. and Nicol, M.J. (2002) Thermodynamics and kinetics of the dissolution of gold under pressure oxidation conditions in the presence of chloride. Canadian Metallurgical Quarterly, 41 (4). pp. 409-415.

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It has been established that gold can be dissolved under conditions typical of those encountered during the pressure oxidation of refractory gold ores provided that the solutions contain chloride ions and that a high ratio of iron(III)/iron(II) is maintained. This study has been conducted in order to understand the behaviour of gold under such conditions and has comprised both thermodynamic and kinetic measurements over a wide range of temperature and chloride concentration. Preliminary electrochemical studies have demonstrated that the effective oxidant for gold under pressure leach conditions is iron(III) and not dissolved oxygen. Measurements of the equilibrium potentials of the gold(III)/gold and iron(III)/iron(II) couples over a temperature range from 25°C to 200°C in acidic sulphate solutions containing various concentrations of chloride ions have confirmed thermodynamic predictions that the equilibrium solubility of gold increases with increasing temperature, chloride concentration and iron(III)/iron(II) ratio. Detailed electrochemical studies of the anodic behaviour of gold and the cathodic reduction of oxygen and iron(III) have been made under the above conditions in an autoclave and have been combined with mixed potential measurements to develop an electrochemical model for the dissolution of gold. The model has been verified by measurements of the actual rate of dissolution of gold as a function of the chloride ion concentration and the temperature. The implications of these results as they relate to the deportment of gold during pressure oxidation and also to the possibility of an alternative process to cyanidation are discussed.

Publication Type: Journal Article
Murdoch Affiliation: Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions
Publisher: Maney Publishing
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