Process flow-sheet for gold and antimony recovery from stibnite

Recovery of gold from refractory ores requires a pretreatment to liberate the gold particles from the host mineral. In particular, in the case of stibnite (Sb2S3), the antimony (Sb) forms stable compounds with sodium cyanide (NaCN) during the cyanidation process; as a consequence, cyanide consumption increases. Pretreatment is usually an oxidation step. As an alternative, chemical leaching can be applied to liberate the gold particles from the sulfur matrix. The aim of the present investigation was to ascertain -- at laboratory scale -- the best conditions for alkaline leaching of a refractory gold-bearing Sb2S3 (13.25% Sb2S3; 30 g t-1 Au) coming from South America. The solutions were constituted by sodium sulfide (Na2S) and sodium hydroxide (NaOH). Main parameters studied were: Na2S concentration, NaOH concentration, pulp density and temperature. After leaching, antimony has been recovered by electrodeposition, in order to increase the economical convenience of the subsequent gold extraction. Antimony recovery has been about 70% Sb for suitable conditions of leaching and electrowinning. Metallic antimony with high purity was obtained. After the study of the leaching parameters, the influence of the pretreatment on the cyanidation process has been evaluated. It was revealed that the chemical pretreatment improves the gold extraction yield and favours a low consumption of reagents: after cyanidation low recovery has been obtained without pretreatment (about 30% Au), while a high gold recovery was achieved in the case of the pretreated samples (about 75% Au), considering also the subsequent steps of carbon concentration-purification and electrowinning. In conclusion, experimental results have shown the technical feasibility of the alkaline leaching pretreatment prior to the conventional cyanidation; moreover, a complete process flow-sheet with low environmental impact, considering technical and economical factors, is proposed.