Manganese and sulfate removal from a synthetic mine drainage through pilot scale bioreactor batch experiments

Mine drainage is a significant problem in the Appalachian Plateau due to elevated metal and solute concentrations. Most metals may be removed by oxidation/precipitation or natural buffering, but Mn is more difficult to remove due to its higher solubility. Some mine drainages in southeastern Kentucky have average sulfate and Mn concentrations exceeding 1,300 and 30 mg L^-1, respectively. Manganese does not readily form sulfidic minerals, and MnS precipitation following sulfate reduction has not proven to be a promising pathway for permanent Mn immobilization. Our study involved batch experiments with five different organic carbon sources in combination with five inorganic substrates to treat a simulated mine drainage with pH 6.2 and Mn and sulfate concentrations of 90 and 1,500 mg/L, respectively. The Mn removal capacity varied widely between treatment mixtures, from <10 to 100%. Sulfate removal showed a similar divergence, ranging from <10 to >80%. The most effective treatment was provided by the biosolids or wood mulch amendments in combination with the creek sediment. Sulfate reduction levels were not stoichiometrically matched with MnS formation, suggesting that the prevalent Mn removal mechanisms were sorption and precipitation as oxide, oxy-hydroxide and carbonate, rather than Mn-sulfide phases.