Enhancement of bacterial iron respiration as a means to inhibit acid mine drainage

The change in the biogeochemistry of acid mine drainage sites by enhancement of bacterial iron reduction have been investigated. The objectives of this research were to: (i) determine the factors that have an impact on iron respiration reactions (initial pH, dissolved oxygen, iron complexation), (ii) determine the role of iron-reducing bacteria in controlling acid generation, (iii) investigate the growth of indigenous iron reducing bacteria by addition of a carbon source in column reactors as a close simulation of the conditions in a waste-rock pile.; Iron reduction by bacteria resulted in a pH increase in some cases. However in some experiments even though iron respiration was observed, no pH increase was observed. Therefore, experiments under varying pH concentrations conducted. Results indicate experiments started at an initial pH of 2 resulted in no pH increase. Iron chemistry around pH 2 was investigated by using Osteryoung Square Wave Voltammetry (OSWV) technique. It was found that iron (III) forms complexes with hydroxide.; Experiments conducted with pyrite as the substrate and mixed cultures of Acidithiobacillus ferrooxidans and Acidiphilium acidophilium, to investigate the competition for oxygen and the effect of the accumulation of microbial organic by-products. No pH increase was observed at the end of the experiments even though iron respiration occurred. Therefore, OSWV experiments were conducted to investigate the complexation of Fe(III) with microbial organic by-products. Results indicated microbial organic carbon is forming complexes with Fe(III) under pH 2.; Column reactor experiments were conducted under three different phases. The first phase was the comparison of the response of reactors containing pyrite mineral to reactors containing waste rock during pyrite oxidation. Results showed that pyrite oxidation in pyrite and waste-rock columns were significantly different regarding concentrations of soluble iron and sulfate produced and the final pH. Second phase of the experiments were conducted only with waste-rock columns. Iron respiration resulted in a pH increase even though the baseline pH was extremely low. The third phase of the column experiments was to investigate the recovery of pyrite oxidation if the carbon source was no longer available. No appreciable pyrite oxidation was initiated 40 days after carbon addition stopped, indicating that addition of soluble carbon has potential for long term restoration of acid generating waste rock.