Extraction of gold from refractory gold ore using bromate and ferric chloride solution

Abstract

During gold extraction by cyanidation, fine gold particles encapsulated in sulfidic minerals are not readily extracted and carbonaceous matter can absorb aurocyanide complexes from the leaching solution. Therefore, high-sulfur and high-arsenic carbonaceous refractory gold ore cannot be treated effectively using cyanidation alone. In this study, an efficient and low-toxicity method for extracting gold from a high-sulfur and high-arsenic carbonaceous refractory gold ore was developed using a solution of bromate and ferric chloride. The gold extraction rate for raw gold ore under optimum conditions (0.25 M potassium bromate, 0.08 M ferric chloride, 0.4 M hydrochloric acid, extraction time of 5 min, stirring speed of 250 rpm, and liquid-to-solid ratio of 5) was 94.5%. For a gold flotation concentrate, the gold extraction rate was as high as 91.8%. Characterization of the leached residues by scanning electron microscopy-energy-dispersive X-ray spectroscopy and X-ray powder diffraction showed that most of the sulfidic minerals were decomposed after leaching. In addition to being efficient and low in toxicity, the proposed leaching method can realize a high gold extraction rate in a very short time without any pretreatment when leaching gold from high-sulfur and high-arsenic carbonaceous refractory ores.