Mineralogical characterization of microbial ferrihydrite and schwertmannite, and non-biogenic Al-sulfate precipitates from acid mine drainage in the Donghae mine area, Korea

Abstract

The waters from abandoned coal mines and dumps contain high amounts of SO4, Al, Fe, Ca, Mg, and Mn. They are precipitated in the stream bottom as oxides and/or sulfates as brown or whitish flocculated biomats. Three types of biomats, the reddish brown, brownish yellow, and white precipitates, are found in the stream bottom of the Donghae coal mine area in Taebaek, Korea. The biomats consist mainly of ferrihydrite with small amounts of goethite and schwertmannite with minor quartz and clay minerals, and Al-sulfate. The ferrihydrite and schwertmannite were directly precipitated from acid mine drainage (AMD) containing high concentrations of Fe and SO4. Goethite was transformed to ferrihydrite and/or schwertmannite depending on pH values. Many spherical and rod-shaped bacteria were observed from the reddish brown biomats. The brownish yellow biomats are composed mainly of spherical type bacteria of 0.5–5 µm in diameter. The reddish brown and brownish yellow biomats show the characteristic shape of twisted stalks of Gallionellaferruginea. Energy dispersive X-ray spectrometer (EDS) analysis of Gallionellaferruginea in the reddish brown and brownish yellow biomats shows Fe>>Si>Ca>Al>P, S and Fe>>Si>S>Al>>P, Ca in concentrations, respectively.