Prevention of acid mine drainage by sulfate reducing bacteria: Organic substrate addition to mine waste piles

Coal or mineral mining operations generate pyritic wastes that are often deposited at open lands near the mine sites. Chemical or biochemical oxidation of pyrites in the waste piles results in the production of sulfuric acid solutions with pH values frequently less than 2. In addition, these low pH leachates often contain high concentrations of toxic heavy metals. This study addresses an innovative approach to prevent the production of acidic leachate from mining waste piles by promoting the growth of sulfate-reducing bacteria (SRB) within the piles. The activity of SRB is known to neutralize acids and, stabilize toxic metals as non-bioavailable metal sulfide precipitates. Batch and column studies were conducted to evaluate the feasibility of inoculating mine waste piles with SRB and stimulating their activities for in situ treatment of acidic leachates containing toxic metals. Inoculation of mine waste materials in batch reactors with SRB cultures resulted in the neutralization of acidic supernatant (pH similar to 3) to pH values of 7.0 and above. During batch incubation of SRB, the dissolved concentrations of Cd, Cu, Ni, and Zn in the supernatant were decreased to undetectable levels. In continuous-flow column experiments containing SRB/mine waste materials, effluent pHs above pH 7 and metal removal efficiencies of greater than 99% for Cd, Cu, and Zn, and 87% for Ni were attained due to the activity of SRB in mine waste columns.