The products of pyrite oxidation, including solution phase Fe2+, Fe3+, S2O32-, S4O62-, SO32- and SO42- and solid phase Fe(OH)3, were measured under controlled conditions in order to investigate the behavior of pyrite in calcareous and alkaline soils. The distribution of sulfur oxidation products is pH dependent and can be interpreted in terms of metastable equilibrium among thiosulfate, disulfane disulfonate and sulfite. Thisulfate and sulfite predominate in the pH range greater than about pH 7 or 8. Sulfane disulfonates are more predominant at more acid pH. Solution concentration data were consistent with the presence of Fe(OH)3. Concentrations of thiosulfate and sulfane disulfonate were consistent with a redox equilibrium among solution iron and sulfure species at pH 6 to 9. Linear or zero-order kinetics were found to be sufficient for description of pyrite oxidation in this study. Linear kinetics were observed as electrical conductivity, solution sulfur products and solution plus solid phase iron products. The measurement of solution iron plus solid-phase iron oxide is a more rigorous approach to the extent of reaction than the measurement of sulfate. The rate of pyrite oxidation is pH dependent, increasing from 10-20 pmol(Fe) m-2 s-1 to 40-60 pmol(Fe) m-2 s-1 between pH 5 and 9. This is consistent with an oxidation mechanism involving the reoxidation of solution Fe2+ via a reaction between an iron hydroxide complex and hydrated oxygen as the rate-determining step. The effect o background electrolytes on oxidation rates at low pH also supports this interpretation. Pyrite oxidation rates in the presence of calcium carbonate, sodium bicarbonate, sodium thiosulfate and calcium-saturated bentonite can be related to the pH effect. Sodium thiosulfate and DTPA appeared to have specific inhibitory effects. Column studies show that the disposal of pyritic mine spoils or tailings by mixing with calcareous material may produce thiosulfate, a good reducing agent for toxic metals. Burial of lime below pyritic materials may protect groundwater quality more effectively than application of lime to the surface.

Mining activities, particularly coal mining, lead to the excavation of large volumes of pyrite rich soils. When exposed to air (oxygen) and water these pyrite complexes are oxidised to form highly acidic and corrosive wastewaters collectively termed acid mine drainage (AMD). Containing elevated levels of sulphates (SO42-) and toxic dissolved heavy metals, AMD seeping from mining sites, active or abandoned, poses a major environmental risk to aquatic bio-systems – not only in South Africa but globally. Chemical neutralization of AMD is expensive and often challenging. Biological sulphate reduction provides a promising and cheaper alternative to the treatment of sulphate rich wastewaters. Little, however, is known about the microbial communities involved in biological treatment systems and the effect of external factors thereon. Studying microorganisms in their natural environment is extremely difficult. The limitations of culture-based methods only provide a limited insight into the bacterial diversity of natural habitats and the microbial communities present. With the progressive advances in molecular biology, non culture-based tools such as DGGE, FISH and more recently t-RFLP allow easier and much more accurate studies of microbial communities within their natural as well as man-made environments. This study specifically investigated the use of t-RFLP to study microbial communities and dynamics within sulphate removing bioreactors. The set up and optimization of a t-RFLP system to specifically study microbial communities from sulphate removing bioreactors were investigated and the applicability of t-RFLP demonstrated. Copyright / Dissertation (MSc)--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted