ABSTRACT
Among the halogens, chlorine was first applied in the 1800s, far before cyanidation was introduced. It was found to be more effective for processing gold bearing sulphide ores and difficult in amenability to gravity concentration and amalgamation. The stability of gold-halide complexes is dependent on the Eh-pH in the solution, composition, and the nature of ores to be processed. The elimination of in situ loss of gold via adsorption with carbonaceous matter and the detoxification of free cyanide are the main advantages for using chlorine leaching. The leaching kinetics of gold in a chloride medium is proportionally dependent on the chlorine-chloride concentrations. A pretreatment of carbonaceous or sulfidic ores is commonly required before undergoing halide leaching to acquire relatively inert ores and less reagent consumption. The corrosiveness and toxicity of halides are difficult from an environmental perspective and need a greater process control on discharge of the final effluent.
