Microbially-Mediated Metal Removal from Acid Mine Drainage

Abstract

Acid mine drainage (AMD) is generated through the microbially-mediated oxidation of pyrite-rich mining wastes and often contains high concentrations of heavy metals and acidity. AMD is traditionally treated with lime. However, such treatment is required indefinitely, representing a considerable economic burden to the mining industry and generates vast volumes of Fe(OH)3 sludges. The ARUM (Acid Reduction Using Microbiology) technology described in this paper provides a low-cost, low maintenance, environmentally acceptable alternative for the amelioration of AMD. ARUM exploits the ability of anaerobic microbial processes to generate alkalinity and ameliorate AMD through acidity reduction and precipitation of heavy metals, resulting from changes in pH and Eh. Anaerobic bacteria use a variety of electron donors and acceptors when molecular oxygen is depleted. In sediments, decomposition of organic matter provides electron donors such as volatile fatty acids and H2, and acid mine drainage (AMD) provides the electron acceptors, SO 4 2− and Fe3+. A test cell system was constructed near Sudbury, Ontario to test ARUM on an AMD seepage with high nickel concentrations. The system comprises two cells for iron precipitation in oxidising conditions and two cells for acidity and metal removal in reducing conditions through ARUM. The ARUM cells have a constructed sediment of organic materials and a floating cattail cover providing organic carbon for the anaerobic bacteria. In 1992, with flow rates of around 1 L/min, the test cell system removed > 88% of the Fe, 77% of the Ni, 39% of the S and 72% of the acidity in the seepage entering the system.