Kinetic limitations of gold leaching in ferric chloride media Part I: Batch reactor studies

Abstract

The global gold industry is under increasing pressure to search for alternative technologies to replace cyanidation due to the inefficiency of cyanide in treating low grade refractory gold ores and increased public scrutiny on the use of cyanide in gold mining. Chloride has been identified as a promising candidate to replace cyanide. Despite extensive efforts to investigate gold leaching in chloride media, gold leaching in ferric chloride media at moderate temperatures relevant to heap leaching has not been well studied. Sponsored by Barrick Gold Corporation, we investigated the thermodynamics and kinetics of gold dissolution in ferric chloride media at moderate temperatures using batch leaching and electrochemical techniques. The Part I of this study reports the effects of four key process variables, initial ferric concentration, total chloride concentration, redox potential of the leaching solution, and the type of chloride salts, on the rate and extent of gold dissolution in ferric chloride media. A series of batch reactor leaching tests was carried out using pure gold as the model mineral. The experimental results showed that the leaching process was either under thermodynamic or kinetic control depending on the leaching conditions. The gold extraction increased with the initial ferric concentration up to 0.3 M, after which a negative effect was observed. This was thought to be caused by the transition from cathodic reduction of the oxidant controlling the kinetics to anodic oxidation of gold controlling the kinetics. Increasing total chloride concentration and the redox potential of the leaching solution also increased the gold extraction. Gold extraction was higher in the presence of the monovalent salts than in the presence of the divalent salts.