Bioleaching of critical raw materials from bauxite resid 2027 Minerals Engin

Bauxite residue (red mud) represents a promising secondary resource for critical raw materials (CRMs). Bio-hydrometallurgy offers an eco-friendly route for CRM recovery. In this study, an Aspergillus sp. was used to bioleach CRMs from bauxite residue (BR) at a relatively low temperature (22 °C), a short contact time (5 days), and high pulp densities (up to 20 w/w%). During one-step bioleaching, fungal activity lowered the pH to 3.1 – 5.3, depending on the BR concentration. The highest recovery efficiencies were achieved at 1% BR, reaching 77% Al, 47% Ti, 50% V, 42% Ga, 61% Y, 65% Zr, 20% La, 18% Ce, and 35% Nd. Increasing the BR concentration led to higher CRM concentrations in the leachate but reduced overall recovery efficiency. Vanadium extraction was maximised at 20 w/w% BR, yielding 48 mg/L in the leachate, corresponding to an 18% leaching efficiency. Ecotoxicological assessment revealed increased toxicity of the leaching residue obtained at 20% BR compared with the original material. Washing further increased residue toxicity and generated a toxic washing effluent, indicating that alternative post-treatment strategies are required. Overall, the results demonstrate that low-temperature, short-term fungal bioleaching at lower pulp densities can provide a promising approach for CRM recovery from bauxite residue.