Biotechnological treatment of a refractory ore: effect on gold leaching processes

This paper deals with the application of biotechnology to enhance gold extraction from refractory sulphide mineral ores. Bioleaching tests were performed with inocula two levels old (7 and 14 days). Iron and sulphate extraction yield resulted to increase with inoculum age, in the investigated range. In any case, arsenic concentration in the leaching liquor was significantly higher than legal limits, evidencing the necessity of a remedial treatment of bioleaching liquor prior to discharge. The effect of bioleaching was investigated on different gold extraction processes: cyanidation, thiosulphate leaching and chlorination. The obtained results showed that biooxidation pretreatment was effective in any case, enhancing gold extraction yields from about 40% to about 80%, after completion of the treatment circuit (biooxidation-leaching). Thiosulphate leaching resulted to be preferable with respect to cyanidation, as concerns both environmental impact and the process kinetics. Chlorination resulted not to be economically feasible due to chlorine consumption, even after biooxidation.