FUNGAL TOLERANCE TO BAUXITE RESIDUE AS A PATHWAY TO CIRCULAR METAL RECOVERY *F. Soto-Montandon1,2; L.J. Webster1,2; R. Gillane1,2; E. Marcellin1; S.T.L. Harrison3 and D. Villa-Gomez1,2 1 Australian Institute for Bioengineering and Nanotechnology; University of Queensland, 4072, QLD, Australia 2 School of Civil Engineering; University of Queensland, 4072, QLD, Australia 3 University of Queensland, 4072, QLD, Australia (*Presenting author: f.soto@uq.edu.au) ABSTRACT Bauxite residue, a by-product of alumina refining, is one of the largest-volume industrial waste streams wastes on Earth. This residue is characterized by high alkalinity and salinity, posing significant environmental risks and high disposal costs. With over 150 million tons generated annually and less than 3% currently recycled, new techniques for its valorization and remediation are needed. However, bauxite residue also represents an untapped source of critical metals necessary for sustainable technologies. This research investigates the potential of two filamentous fungal strains, Aspergillus niger and Penicillium oxalicum, for the valorization, remediation, and rehabilitation of bauxite residue disposal areas. Specifically, this study evaluates their tolerance to high salinity, alkalinity, and bauxite residue, determines their neutralization capacity, and highlights their potential applications. KEYWORDS Bioleaching, Bauxite residue, Waste valorization, Critical Minerals, Circular economy. 1. INTRODUCTION Bauxite residue (BR) is the highly alkaline solid waste produced during the alkaline digestion of bauxite ore to produce alumina during the Bayer process. This residue is characterized by its high alkalinity (pH 10.5-12.8), high salinity, with exchangeable sodium percentage values ranging from 53% to 91%, and high electrical conductivity values between 1.4 and 28.4 mS/cm (Jiang, Qin, et al., 2023). Over 4 billion tons of alumina refinery waste are currently stockpiled worldwide, with an additional 150 million tons generated annually, making it one of the most abundant industrial wastes globally (Bandopadhyay, 2006; Lyu, Hu, Wang, & Sun, 2021). Yet recycling rates remain below 3%, underscoring the critical need for sustainable management strategies (U. S. Environmental Protection Agency, 2024). Untreated BR pose significant hazards, affecting natural ecosystems and threatening the safety of nearby communities, soil, and groundwater resources through the leaching of caustic liquor, toxic metals, and alkaline dust (Päivärinta-Antikainen et al., 2023; Pradhan, Tripathy, Ram, Digal, & Das, 2024). Moreover, the cost of safely disposing of alkaline BR is significant, varying between 1% and 5% of the production value of alumina (Bandopadhyay, 2006; Tsakiridis, Agatzini-Leonardou, & Oustadakis, 2004). Given the low reuse rate, the significant hazards it poses, and the high costs associated with
RkJQdWJsaXNoZXIy MTM0Mzk2