Bioleaching-based dissolution of tungsten from scheelite using spent microbial media and H2SO4: process optimization and kinetic insights

Tungsten extraction from scheelite remains challenging due to the mineral’s refractory nature. Conventional extraction methods typically rely on high temperatures, elevated pressures, and alkaline reagents, resulting in significant energy consumption and operational complexity. While previous studies have demonstrated tungsten bioleaching using actively growing microorganisms, limited information is available regarding the role of spent microbial media and microbial metabolites in scheelite dissolution. Therefore, this study investigates the dissolution of tungsten from scheelite using spent media obtained from Acidithiobacillus ferrooxidans (BS) and Aspergillus niger (AS) in combination with sulfuric acid under atmospheric conditions. The influence of key process parameters, including temperature, sulfuric acid concentration, reaction time, solid content, and spent medium type, was evaluated to identify favourable conditions for tungsten dissolution. Under the investigated laboratory conditions, tungsten dissolution of up to 99% was observed at 55 °C, 2 M sulfuric acid, 1 wt% solid content, and a particle size below 75 µm after 180 min of leaching. Kinetic analysis showed that the diffusion-control model provided the best overall fit to the experimental data, suggesting that mass-transfer processes play an important role in tungsten dissolution under the investigated conditions. Activation energies of 59.95 kJ/mol and 55.56 kJ/mol were determined for the AS and BS systems, respectively. The results indicate that spent microbial media can enhance scheelite dissolution in the presence of sulfuric acid and provide preliminary insights into the potential role of microbial metabolites in scheelite dissolution. The findings contribute to the understanding of bio-assisted scheelite processing and provide a basis for future mechanistic investigations. Unlike previous studies focused on active microbial bioleaching, this work evaluates the contribution of spent microbial media to scheelite dissolution and provides kinetic information for this bio-assisted leaching system. The study is intended as an initial assessment of the potential role of microbial metabolites in enhancing scheelite dissolution rather than a definitive mechanistic investigation.