Biooxidation of Sulfide-Based Refractory Gold Ores at Low Temperature

Abstract

Gold recovery from iron-sulfide-bearing refractory ores presents significant challenges, particularly at low temperatures where traditional pretreatment methods, such as microbial biooxidation, exhibit reduced efficiency. This research systematically investigates and compares two biooxidation strategies—microorganism-assisted biooxidation using Ferroplasma acidiphilum and an enzymatic biooxidation technology (EnBiTe) based on glucose oxidase (GO) immobilization—to enhance gold liberation from refractory ores. Bench-scale experiments demonstrated that microbial biooxidation achieved optimal pyrite dissolution (~75%) under controlled conditions, including a 15-day operating time, a pyrite content of 7.2 wt.%, and a pH of 1.47. However, microbial oxidation efficiency significantly decreased at temperatures below 10°C due to the metabolic limitations of acidophilic microorganisms. To mitigate these limitations, extracellular polymeric substances (EPS) overproduction was induced through monosaccharide supplementation, with D-sucrose yielding the highest ferric ion production and pyrite dissolution. Despite these improvements, the microbial biooxidation approach remained highly sensitive to environmental fluctuations and required precise control of pH, aeration, and nutrient availability to maintain microbial activity, making it less viable for cold-climate applications. Moreover, machine learning models, including Artificial Neural Networks (ANN) and Genetic Programming, were employed to predict biooxidation efficiency based on key parameters such as time, pH, oxidation-reduction potential (ORP), pyrite content, and monosaccharide concentrations. To address the limitations of microbial biooxidation in low-temperature environments, enzymatic biooxidation technology (EnBiTe) was developed as an alternative pretreatment strategy. This method employed glucose oxidase (GO) immobilized on modified sawdust to catalyze the oxidative dissolution of pyrite and arsenopyrite, thereby liberating encapsulated gold. The process optimization study revealed that EnBiTe achieved up to 89.2% pyrite dissolution for high-grade ore and 73.4% for low-grade ore under conditions including a 100 mM glucose substrate concentration, 5 g immobilized enzyme, and a pH range of 5–6. Unlike microbial biooxidation, EnBiTe functioned effectively at low temperatures (~5–10°C) without requiring extensive aeration or pH adjustments. Furthermore, a modular enzyme system incorporating catalase (CAT) was introduced to mitigate oxidative stress and enzyme degradation, extending process stability. Column test evaluations confirmed that EnBiTe not only enhanced pyrite oxidation but also facilitated faster gold liberation, demonstrating a significant advantage over microorganism-assisted methods. The controlled enzymatic approach also reduced operational uncertainties, providing a scalable and environmentally sustainable alternative to conventional biooxidation. A comparative analysis of the two biooxidation strategies indicated that enzymatic biooxidation significantly outperformed microbial biooxidation in low-temperature conditions, achieving higher pyrite oxidation rates and gold recovery efficiencies. Cyanidation trials following biooxidation showed that gold recovery reached 90% after EnBiTe pretreatment, compared to 60% following microbial biooxidation under optimized conditions. The findings of this research establish EnBiTe as a promising alternative to microbial biooxidation for gold recovery from refractory sulfide ores, particularly in cold regions where traditional methods struggle. By offering a more efficient, scalable, and environmentally friendly approach, this research contributes to the advancement of biohydrometallurgical processing and provides a foundation for potential industrial applications of enzymatic biooxidation in the mining sector.