AMMONIACAL THIOSULPHATE LEACHING OF A COPPER-RICH GOLD ORE

In this current study, the extraction of gold from a high grade copper-rich gold ore by copperassisted ammoniacal thiosulphate leaching was studied by adopting Taguchi L9, (3) experimental design approach. The effects of concentration of thiosulphate, (10-500 mM S2O3), copper (0-25 mM Cu), and ammonia (5-1000 mM NH3) on the extent of gold extraction were investigated at three levels. Statistical analysis of data was performed based on the analysis of variance (ANOVA). Cyanide leaching of the ore resulted in a gold extraction of only 22% while gold extractions as high as ~62% were achieved by ammoniacal thiosulphate leaching. The concentrations of thiosulphate (S2O3) and ammonia (NH3) were identified to be statistically significant factors affecting the extraction of gold, while the effect of addition of copper (Cu) is insignificant. This could be linked with the ready dissolution of copper (i.e. 100%) during ammoniacal thiosulphate leaching. Although ammoniacal thiosulphate leaching appears to be more effective than cyanide leaching for gold extraction, it also suffers from high thiosulphate consumption.

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