The development of an environmentally friendly leaching process of a high C, As and Sb bearing sulfide gold concentrate

• The process of alkaline pressure oxidation–thiosulfate leaching was developed.
• Sulfide minerals were effectively oxidized by alkaline pressure oxidation.
• The reagent dosage of alkaline pressure oxidation was less than stoichiometric.
• The secondary encapsulation of gold was relieved during alkaline pressure oxidation.
• The environmental risk of this developed leaching process was very low.

An environmentally friendly leaching process, consisting of the pretreatment of alkaline pressure oxidation and thiosulfate leaching, has been developed to efficiently extract gold from a high carbon, arsenic and antimony bearing sulfide gold concentrate. The Au extraction from the concentrate by direct cyanidation was very low mainly due to the encapsulation of gold by associated minerals and the preg-robbing effect of graphite and organic carbon. The pretreatments of permanganate oxidation and oxidative roasting both could effectively liberate encapsulated gold and eliminate the preg-robbing effect on cyanidation. However, the reagent dosage of permanganate oxidation was high and the final oxidation solution contained substantial quantities of toxic ions. The flue gas of oxidative roasting also contained a lot of poisonous oxides, and the extremely drastic reaction environment of roasting led to the secondary encapsulation of gold by newly generated oxides. The pretreatment of alkaline pressure oxidation effectively liberated encapsulated gold with less than stoichiometric reagent dosage and simultaneously relieved the secondary encapsulation of gold, but could not completely remove graphite and organic carbon. Because carbonaceous matter had a weak affinity for gold thiosulfate complex, the Au extraction by thiosulfate leaching after the pressure oxidation achieved 86.1% whilst the thiosulfate consumption was 35.3 kg/t-concentrate. This process of alkaline pressure oxidation–thiosulfate leaching neither used toxic reagent nor released poisonous gas, and furthermore its effluents contained few toxic ions.