Field Demonstration of Direct Mine-Pool Treatment to Mitigate Acid Mine Drainage

Abstract

One of the most significant environmental challenges faced by the mining industry is the management of acid drainage from former underground mine workings and waste rock piles. The conventional methods typically employed to manage acid-mine drainage (AMD) and reduce its impact on the environment include diverting drainage through systems that can neutralize the acidity and precipitate metals. These methods can require a significant commitment of land and resources, and focus on point-sources that can be diverted for treatment. They cannot account for fugitive subsurface flow which can also be a significant contributor to the overall environmental impact of AMD. By comparison, in-mine treatment to neutralize acidity, break the acid generation cycle, and improve the quality of the discharge would be more effective and less costly than conventional approaches to AMD management and source control. ARCADIS completed a three-month field-scale demonstration of a patented process for in situ treatment and prevention of acid mine drainage (AMD) within the workings of an abandoned bituminous coal mine located in the eastern United States. The phased treatment approach decreased oxygen concentrations above the mine pool from over 20% (ambient air conditions) to less than 5% for the entire second half of the demonstration, raised the pH from a baseline of approximately 2.5 to over 6, and then maintained a pH above 5 through microbially-produced alkalinity. Ferric iron was reduced to non-detectable concentrations with a steady decreasing trend in soluble aluminum concentrations (approximately 30% reduction in the study period). Additional precipitation of metals in solution would be expected with longer operation, in response to further pH moderation and increases in sulphate reduction. These results indicate that in-mine treatment is effective at breaking the AMD cycle and has significant potential for managing the acidity from underground mine workings.