Rinding and cyanide leaching of bolkardag gold andsilver ores

In this study, microwave pre-treatment which was conducted for Bolkardag (Nigde, Turkey) gold ore was investigated for the effect of ore grindability and cyanide leaching. Three different particle size fractions (-8+4.7 mm, -4.75+2 mm and -2+1 mm) were used for microwave pre-treatment. Each sub-sample were exposed to 5 different power levels of microwave energy (90, 180, 360, 600 and 900 W) at exposure times of 5, 10, 15 and 30 minutes. Grindability characteristics of the treated samples were investigated by Berry and Bruce comparative grindability method. Cyanide leaching experiments were conducted on samples that the highest decrease in the Bond work index was achieved according to this method. The temperature values of the samples are compared after microwave experiments. It was observed that the temperature values of all samples increased with the increase in microwave power level and exposure time. Besides, it was observed that the temperature increased with increasing particle size at the same power levels. The highest temperature value of 232ºC was observed for the -8+4.75 mm size fraction sample after microwave treatment for 30 minutes at 600 W. In grindability experiments, it was clearly seen that increasing microwave power level and exposure time caused reduction in comparative Bond work index. The maximum reduction in Bond work index (73.5%) was achieved by 600 W at 30 minutes of microwave treatment for the -8+4.75 mm size fraction sample. After 77 hours cyanide leaching, gold and silver extraction rates increased respectively, 7% and 9% compared to the un-treated samples' results to microwave treated samples' results. Additionally, the effect on the cyanide leaching efficiency of adding lime to the samples during microwave pre-treatment was investigated. Cyanide leaching results of the samples that lime added and non-added during microwave pre-treatment was observed, similarly. Applying microwave pre-treatment before cyanide leaching, the gold and silver extraction rates and leaching efficiency can increase, leaching time is shortened. In addition, it is estimated that considering the decrease in Bond work index microwave pre-treated ore has easier breakage aspect and this condition will decrease the grindability cost.