Control of acid rock drainage from mine tailings through the addition of dissolved organic carbon

Abstract

Acid mine drainage detrimentally affects thousands of surface watercourses throughout the world and costs tens of millions of dollars annually in site remediation expenditures. This process is accelerated by the activity of iron- and sulfur-oxidizing bacteria which grow chemolithotrophically in mine tailings. Low cost, environmentally acceptable, and low maintenance treatment technologies are needed to both treat acid mine drainage and prevent its occurrence. The addition of dissolved organic carbon to mine tailings has the potential to stimulate beneficial heterotrophic populations of bacteria at the expense of iron and sulfur oxidizers. These experiments investigated the use of three organic carbon sources: molasses, cheese whey and methanol in controlling acid mine drainage from two tailings sources. All three organic carbon sources are easily dissolved in water, relatively inexpensive, and easily transported to remote locations. Mine tailings were acquired from the Fox Lake Mine (Manitoba) and the Mammoth Mine (Montana) and were packed into columns. Columns were watered on a weekly basis and dissolved organic carbon was periodically applied. The treatments increased pH up to 3 units over untreated controls, while simultaneously decreasing oxidation-reduction potential over 300 mV. Sulfate reducing bacteria were stimulated in columns treated with organic carbon, as were heterotrophic populations. Some iron- and sulfur-oxidizing organisms were found to be capable of heterotrophic growth, a condition which compromised treatment effectiveness. Individual organic carbon treatments were found to vary in pH/ORP effect from several months to over 2 years. Phylogenetic analysis of column samples suggests both a robust population of bacteria in untreated mine tailings and the growth of SRB resulting from treatment.