Bio‑oxidation of Double Refractory Gold Ores by a Mixed Culture Including an Acidophilic Heterotroph before Cyanidation

Double refractory gold ores (DRGOs) present significant challenges in gold recovery due to the encasing of gold grains by sulfides and carbonaceous matter, leading to a phenomenon known as “gold robbing.” Traditional methods involving sequential pretreatment of DRGOs have shown challenges, prompting the need for more efficient approaches. This study aims to explore a novel one-step bio-oxidation treatment designed to liberate gold grains by employing a mixed culture comprising an iron-oxidizing bacterium (Acidimicrobium ferrooxidans), a sulfur-oxidizing bacterium (Acidithiobacillus caldus), and an acidophilic heterotroph (Alicyclobacillus acidoterrestris) under strongly acidic conditions. The methodology allowed for the complete removal of sulfide minerals at low pH, leading to the successful exposure and liberation of gold grains. This one-step process represents a significant advancement in treating DRGOs, simplifying what is typically a complex multistep procedure and demonstrating substantial improvements in processing efficiency. The findings suggest that utilizing a mixed culture in bio-oxidation can effectively enhance the recovery of gold from refractory ores, potentially transforming the approach to processing DRGOs in metallurgical practices.