CHARACTERIZATION OF MN OXIDES ACROSS A COAL MINE DRAINAGE REMEDIATION SYSTEM IN GLASGOW, PA

Pennsylvania coal mine drainage sites often contain high concentrations of Mn and other metal contaminants. Passive treatment systems have been built to remediate the acidic wastewater. These systems may contain a dolostone bed to increase the pH of the stream water, and/or organic substrates such as coconut coir to stimulate biotic precipitation of Mn oxides. The cation-exchange and sorption properties of Mn oxides then promote the removal of other metal contaminants. In this work, we examine one such passive treatment system in Glasgow, PA (near Bellwood) with a focus on characterization of the Mn oxide phases. Mn oxides were collected across a 6-trench dolostone bed and analyzed with X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and Raman spectroscopy. Water samples were also collected from the trenches and analyzed for pH and metal concentrations with inductively coupled plasma-optical emission spectroscopy (ICP-OES).

XRD analyses of the Mn oxides typically showed strong 10 Å basal peaks, consistent with a buserite-like layer structure, resembling that of synthetic Ca-birnessite. Mn oxides typically formed as aggregates of nano-sized platelets and as coatings on bacteria cells and other microorganisms. Raman maps showed that triclinic birnessite was intermixed with hexagonal birnessite and todorokite at the micron scale. Elemental analyses of Mn oxides revealed that triclinic birnessites had higher Ca and Mg concentrations than did hexagonal birnessite, along with a stronger association with Al, Ni, and Co. Our proposed formula for the hexagonal birnessite-like phase is (Mn²⁺_0.26Mn³⁺_0.28Ca_0.04Mg_0.02Na_0.01K_0.01)(Mn⁴⁺_1.50Mn³⁺_0.18□_0.32)O₄·nH₂O. For the triclinic phase, our proposed formula is (Ca_0.16Mg_0.17K_0.02)(Mn⁴⁺_1.32Mn³⁺_0.68)O₄·nH₂O. Characterization of samples from across the site showed a range of relative abundances of triclinic versus hexagonal birnessite. Analyses of water samples indicated that the Mn removal bed was successful in increasing pH across the trenches, and at removing Na, K, Ni, Fe, Al, and Mn.