Persulfate Activation by Major Soil Minerals

by MUSHTAQUE AHMAD, M.S. Washington State University December 2008 Chair: Richard J. Watts Oxidant interaction with subsurface materials is a major factor influencing the effective application of in situ chemical oxidation (ISCO) for contaminant destruction. The newest and least explored ISCO oxidant source is persulfate. Persulfate interaction with subsurface minerals was investigated as a basis for understanding persulfate activation in the subsurface. The mineral-mediated decomposition of persulfate and generation of oxidants and reductants was investigated with four iron and manganese oxides and two clay minerals at both low pH (<7) and high pH (>12). At both low and high pH, persulfate decomposition was minimal in the presence of all six minerals. The manganese oxide birnessite was the most effective catalyst for degrading the hydroxyl radical probe nitrobenzene, indicating hydroxyl radical generation at both low and high pH regimes. The iron oxide goethite was the most effective catalyst for degrading the reductant probe hexachloroethane. Several fractions of a natural soil were used to confirm the catalytic behavior of synthetic minerals. Natural soil fractions did not effectively catalyze the generation of hydroxyl radicals or reductants. However, soil organic matter was found to promote reductant generation at high pH. The results of this research demonstrate that synthetic iron and manganese oxides can activate persulfate to generate reductants and oxidants, however, iron and manganese oxides