Bioleaching Rare Earth Elements from Abandoned Coal Mine Drainage as an Unconventional Feedstock for Biomining

Abandoned coal-mine drainage (CMD) is a domestic source of rare earth elements (REEs) that can be biomined. Pennsylvania has ~11,000 abandoned mines, with ~500 CMD passive remediation systems (PRSs). REEs found in CMD accumulate as solid precipitants in PRSs. Microbial biogeochemical manganese (Mn) resolubilization could co-resolubilize REEs, producing an affordable and valuable leachate. However, microbial mechanisms that contribute to REE resolubilization are poorly understood. We have previously isolated six acidogenic bacteria (four Bacillus spp. and two Corynebacterium spp.) that solubilize Mn oxide. Here, we determined all acidogenic isolates can solubilize Mn from Glasgow CMD solids, and that B. mycoides JR07 and B. pseudomycoides KB7 can solubilize (bioleach) REEs from four REE-enriched acidic CMD PRSs (Glasgow, Scootac, Sterrett, Kentucky Hollow). Successful REE bioleaching by B. mycoides JR07 and B. pseudomycoides KB7 is likely due to lactic acid production, interactions with CMD solids, and biofilm formation. We found that aluminum (Al) solubilization is a better indicator of CMD REE release than Mn. Determining the microbial metabolism and genes involved in the release of REEs from CMD solids is crucial to optimizing biomining. Our work addresses the growing need to develop novel REE recovery methods from unconventional domestic sources.