Chlorination leaching, one of non-cyanidation processes, which was in use until the end of 19th century after its development in the middle of the 19th century, was deprecated after the cyanidation process was born. However, in the eighties of the 20th century it was found that chlorination leaching had a good effect on fine grains of gold ores, and researchers’ interest in it revived, leading to some successes.
Compared to cyanidation leaching, chlorination leaching of gold by chlorine or hypochlorite has faster gold leaching rate and less pollution. What is more, it is cheaper and simpler.
Kim Chang Sok, a researcher at the Science Engineering Institute, has conducted thermodynamic and experimental research on chlorination leaching of refractory gold concentrates. Then, he has observed the influence of the redox potential on gold leaching and confirmed reasonable conditions for the potential.
The results demonstrate that for a higher leaching rate of gold, leaching time should be more than two hours and redox potential should be controlled at 1.0V or more. Under the conditions of the initial concentration of active chlorine 0.5%, the value of pH 4.0, the leaching time at least two hours and the redox potential more than 1.0V, the leaching rate of gold could reach over 96%.
You can find more information about this in his paper “Research on Chlorination Leaching of Pressure Oxidized Refractory Gold Concentrate” presented to the SCI Journal “Hydrometallurgy”.