Gold leaching from oxide ores in alkaline glycine solutions in the presence of permanganate

In this study, the effect of using strong oxidants with alkaline glycine solutions on the leach rate and recovery of gold was studied in the absence of cyanide. Prior research indicated that when using only alkaline glycine and air at ambient temperature in the absence of catalysts, leaching times would be too long for conventional agitated tank leaching of ores. The ores used in this study were from oxidised geological domains, which would not be expected to excessively consume oxidant. The influence of the oxidants such as potassium permanganate, hydrogen peroxide, sodium chlorate, potassium iodide, and potassium ferricyanide were initially evaluated in a screening test. The highest gold extractions were observed with potassium permanganate, where a recovery of 85.1% was achieved at 1.5 kg/t glycine and 3 kg/t permanganate at 30% solids, pH 10.5 and ambient temperature using a bottle roll process. This compared to a 87.4% recovery against a conventional cyanidation benchmark. Other oxidants only achieved a recovery of 11% at best, so permanganate was the focus of the optimisation work. The solution pH had very little effect on gold recovery between 9.5 and 11.5 and the main products of this reaction were determined when lime was used as pH modifier.