Effect of galena on thiosulfate leaching of gold

Galena and reference quartz were artificially added into the ammoniacal thiosulfate solution to clarify the role of galena on thiosulfate leaching of gold. The effects of galena on thiosulfate decomposition and gold leaching and the possible effect mechanisms were studied by the thermodynamic calculation, leaching tests, SEM-EDS and XPS analyses. Results showed that from the onset of gold leaching, the leaching kinetics was restricted severely in the presence of galena. This is caused by the fact that galena is easily oxidized by copper(II) and the dissolved oxygen, thus the mixed slurry potentials initially experienced a significant decline to relatively stable lower levels of 230-240 mV which are nearly 50 mV lower than that of the quartz slurry. This is disadvantageous to gold leaching and results in undesirable gold dissolutions during the process. The results suggest that the decrease of slurry potentials from the presence of galena is the principal cause of a reduction in the gold leaching rate.