Synergistic strategy for enhanced bio-oxidation of refractory gold concentrate with high arsenic and sulfur: ferric oxidation with mixed organic nutrients supplementation

Abstract

The bio-oxidation of refractory gold concentrates with high arsenic and sulfur contents is inefficient, due to its slow reaction kinetics and the arsenic toxicity. To address this limitation, present study proposed a novel strategy involving ferric (Fe³⁺) pre-oxidation synergistically combined with the simultaneous addition of hydrolyzed rice husk (HRH) and urea. Chemical and interfacial analyses revealed that ferric oxidation removed 13.4 ± 1.4 % of arsenic (As) from the concentrate and disrupted the physicochemical structures of mineral surfaces (pyrite and arsenopyrite), thereby creating favorable conditions for subsequent microbial growth, adsorption, and mineral dissolution. Bio-oxidation analysis demonstrated that urea supplementation significantly stimulated the growth of iron-oxidizing microorganisms, predominantly Leptospirillum spp., while HRH addition promoted the proliferation of the mixotrophic Sulfobacillus spp. and enhanced its adsorption capacity by improving mineral surface hydrophilicity. The combined effect of HRH and urea effectively optimized the microbial community structure, increasing species diversity and evenness, which in turn enhanced Fe³⁺/Fe²⁺ cycling and the metabolism of the sulfur passivation layer. This effectively enhanced the reaction kinetics of the sulfide minerals. Consequently, this synergistic strategy improved the bio-oxidation efficiencies of Fe and S by 1.17-fold and 1.42-fold, respectively, compared with conventional bio-oxidation, and elevated the cyanide leaching levels of Au and Ag to 97.3 ± 0.5 % and 93.6 ± 0.8 % (31.0 % and 30.7 % improvements). This research provides a novel technical approach and theoretical foundation for the efficient and environmentally friendly processing of complex refractory gold ores.