MICROBIAL REDUCTION OF MANGANESE OXIDES FROM AMD SOLIDS FOR THE BIOMINING OF CRITICAL MINERALS

Abandoned Coal-Mine Drainage (AMD) is a source of critical minerals (CMs) that can be biomined to increase domestic CM production for the growing technology industry while mitigating hazardous waste. Pennsylvania has ~11,000 abandoned mines, ~500 of which are currently being treated with passive remediation systems (PRS), designed to increase the pH and precipitate AMD waste onsite. Manganese (Mn) that precipitates from AMD waste can co-precipitate with CMs, leading to accumulation as solids in PRS. Solids high in Mn/CM could produce a valuable leachate if resolubilized, which can occur through microbial driven geochemical changes, and it is expected that Mn resolubilization will lead to a co-resolubilization of the CMs. Investigation and stimulation of this microbial resolubilization could result in an affordable CM release process that does not require chemical additives. However, the microbial mechanisms that contribute to Mn resolubilization are poorly understood. Here, we have isolated bacteria capable of resolubilizing Mn from AMD PRS. Five of the bacterial isolates have been identified as Bacillus spp. and two as Corynebacterium spp. that ferment glucose to reduce/solubilize MnO₂ by acidogenesis. The bacterial isolates are also capable of co-resolubilizing CMs (Y, Zr, Sb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) from AMD PRS solids through their production of organic acids. Determining the microbial metabolism and genes involved in the resolubilization of manganese is crucial to optimize the biomining of CMs from AMD solids. This work addresses the growing need to develop novel CM recovery methods from domestic sources.