OPTIMIZING MANGANESE REMEDIATION FROM COAL MINE DRAINAGE: THE ROLE OF MINERAL STRUCTURES, MICROBES, AND LINER ROCKS

Coal mine drainage (CMD) impacted waters remains a persistent issue throughout much of the Appalachian coalfield. Passive manganese (Mn) removal beds (MRBs) are deployed in several CMD remediation sites throughout the region, designed to promote the oxidation of aqueous Mn(II) to solid Mn(III/IV) (oxyhydr)oxide minerals via flow through ponds lined with carbonate rocks (to buffer the pH), and microbial Mn oxidizers (either colonized by native communities or actively seeded from known Mn oxidizers). We investigated the role of water chemistry on Mn remediation at a passive MRB near Altoona, PA. We find that water pH and aqueous Mn(II) concentrations vary throughout the dolostone-lined MRB flow through ponds, with X-ray diffraction, Raman spectroscopy, and Mn K-edge X-ray absorption spectroscopy (XAS) finding consistent and predictable differences in Mn oxide mineral structures (e.g., hexagonally symmetric vs. triclinic birnessites) related to differences in water chemistry. These Mn oxides play an important role in sequestering other metal contaminants (e.g., Ni, Zn, and Co). Filter sterilizing CMD from Altoona, PA yields little to no Mn oxidation, indicating that microbial Mn oxidizers are critically important to Mn remediation. With water chemistry potentially impacted by carbonate liner rocks, we investigated the kinetics and overall efficacy of Mn remediation from synthetic CMD with various potential liner rocks (limestone, dolostone, zeolite, and quartz sand as a control), with and without the Mn oxidizing fungus, Stagonospora sp. SRC1lsM3a. We find that fungal systems outperform their abiotic counterparts and produce solids with higher average Mn oxidation states. The limestone-fungal system successfully remediates aqueous Mn down to just 2 ppb by day 16 while dolostone and zeolite systems never achieve World Health Organization standards for aqueous Mn (<80 ppb). However, zeolites do result in rapid Mn removal from solution (>95% Mn within 24 hours). While all liner rock systems produce appreciable fractions of solid-associated Mn(II/(III/IV), the Mn(II) in zeolites is susceptible to desorption with changing water chemistry. These results highlight the importance of water chemistry and microbes in controlling the effectiveness of CMD passive remediation and resulting Mn oxide structures.