Biodegradation of sulfides and carbonaceous matter in refractory gold ores

Biooxidation is currently one of the major pretreatment processes for refractory sulfidic gold ores and concentrates. Due to galvanic interactions, different sulfide minerals associated with gold ores respond differently to microbial oxidation. In this investigation, Thiobacillus thiooxidans , Thiobacillus ferrooxidans and Leptospirillum ferrooxidans were used to study the effect of the ratio pyrite to arsenopyrite on biooxidation. It was realized that increasing pyrite concentration led to faster reaction kinetics and achievement of the target values for the physicochemical variables such as redox potential, pH, and [Fe3+] to [Fe2+] ratio that are necessary for the smooth operation of a commercial bioreactor.; Biotreatment of carbonaceous matter in gold ores has not been applied in commercial gold processing and there is paucity of information on the subject. Streptomyces setonii was used to degrade carbonaceous matter in gold ores and various types of coal were used to study the effect of carbonaceous characteristics on biodegradation. Microbial alteration of coal ranged from 2% to 97% and the extent was in the order: lignite > bituminous coal > anthracite. There were significant decreases in gold adsorption by the coal samples after contact with bacterial cultures and the effectiveness was in the order; bituminous coal > lignite > anthracite. In general, the results for two refractory ores (samples A and B) confirmed the findings.; The biodegradation of both sulfides and carbonaceous matter in the ores tested led to improved gold recovery in the subsequent cyanidation process. After sulfide oxidation, gold recovery for sample A was 81.1% and this increased to 94.7% following degradation of both sulfides and carbonaceous matter. Sample B was non-sulfidic, and extraction increased from 24.8% to 51.6% after degradation of carbonaceous matter. Biodegradation of both sulfides and carbonaceous matter before gold extraction as performed in this investigation is a novel process for pretreating refractory gold ores.