Pre-oxidation of high-sulfur and high-arsenic refractory gold concentrate by ozone and ferric ions in acidic media

Owing to precious metals and hazardous elements contained in high-sulfur and high-arsenic refractory gold concentrate (HGC), effective treatment of HGC can have both economic and environmental benefits. In this paper, pre-oxidation HGC by ozone and Fe (III) in acidic media and subsequent cyanide leaching of the pretreated ores were investigated. An L9 (four factors in three levels) standard orthogonal array was employed to evaluate the effects of ferric concentration, reaction temperature, reaction time, and liquid to solid ratio on ferric extraction from HGC. Statistical techniques were used to determine that reaction temperature was the most significant factors affecting ferric extraction. Furthermore, the results of factorial experiments showed ferric extraction increased with an increase of ozone concentration, liquid to solid ratio and temperature, but was independent of stirring speed when the speed was above 860 rpm. Also, the selected oxidized residues after the pretreatment process were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD) and subjected to subsequent cyanide leaching tests. Gold extraction after pre-oxidation under optimum conditions increased from 19.5% of direct cyanide leaching to 96.5%.