Lixiviação de minério oxidado de ouro-cobre com tiossulfato de amônio

Abstract

The present study aimed verify the application of ammoniacal thiosulfate leaching to a sample of an oxidized gold-copper ore with high cyanide soluble copper content (0.1%) in bench scale experiments. The leaching experiments carried out aimed establishing the effects of [NH3]/[S2O3 2-] ratio, copper concentration in solution, sulfite addition, and aeration of the slurry on metals extraction and thiosulfate consumption. Continuous thiosulfate addition, as an attempt to keep the concentration constant, was also experimented. It was shown that, for this particular sample, the use of thiosulfate allows to extract as much gold as cyanidation, and that the copper available in the ore is enough to catalyze gold leaching and also to cause excessive thiosulfate consumption (33 to 101kg/t). Copper concentrations below 100mg/L - obtained by leaching the ore with sulfuric acid prior to thiosulfate leaching resulted in little gain in thiosulfate consumption, but with negative effects on gold dissolution kinetics. Varying [NH3]/[S2O3 2-] ratio raised slurry redox potential (Eh) that may indicate an increase in the [Cu2+]/[Cu+] ratio. Conversely, leaching in inert atmosphere, achieved by nitrogen injection, resulted in lower slurry Eh. However, none of these conditions resulted in increased gold extraction, or in lower thiosulfate consumption in comparison with standard conditions (open vessel; 25oC; 1atm; 0.23mol/L S2O3 2-; 0.67mol/L NH3), in which 90% gold extraction was obtained. Continuous thiosulfate addition aimed to promote leaching at constant thiosulfate concentration but lower than in the control experiment (0,1mol/L), did not work as expected, since it did not result in high gold extraction and low thiosulfate consumption.