Extractive waste residues are large waste streams and contain significant amounts of metals, which when poorly managed, could constitute various environmental hazards such as acid mine drainage. Reprocessing could reduce the environmental risks associated with mine wastes, as well as contribute substantially to the ever-growing global demands for metals. Biomining, the use of microorganisms for the extraction of metals from primary and/or secondary ores, may be useful in the treatment of extractive waste residues. This is due to its competitive cost-effectiveness for the processing of low-grade ores, in addition to its minimal carbon footprints, in comparison to other extractive metallurgies such as pyrometallurgy. Chemolithoautotrophic acidophilic bacteria are extensively studied and can effectively catalyze the solubilization of metals from ores or waste materials. However, bioleaching activities with acidophilic bacteria are performed at low pH (pH ≤ 2) which could lead to the acidification of the environment. Also, the tolerance of many acidophilic bacteria to high chloride concentrations is limited, therefore freshwater is mostly used for bioleaching. We hereby present a new bioleaching approach for the treatment of metal-contaminated mine wastes at a higher pH (pH ≥ 4) and chloride concentration, using two marine (halophilic) sulfur-oxidizing bacteria: Thioclava electrotropha and Thioclava pacifica. Bioleaching with the two bacterial strains seems promising, as up to 30% Co and 10% Cu, Pb, Zn, Cd, As, K and Mn were solubilized from a fresh waste rock sample. Though still requiring process optimization, this new biotechnology offers remarkable benefits, as it could prevent extreme acidification of the environment while also being applicable in seawater. The mine waste residues cleaned via this approach will be analyzed for subsequent valorization into various circular-economy applications such as inorganic polymer, green cement, and ceramics.

Novel bioleaching approach for the treatment of mine waste

ACS Spring 2022

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