Transformation of carbon tetrachloride by bisulfide treated goethite, hematite, magnetite, and kaolinite

This study investigated the transformation of carbon tetrachloride (CT) by goethite, hematite, magnetite, and kaolinite treated with bisulfide to form coatings of iron monosulfide (FeS) and other Fe(II) species. These coatings contribute to abiotic natural attenuation in anaerobic environments. Batch kinetic experiments were performed under anoxic conditions at pH 8.0. Surface-area-normalized pseudo-first-order rate constants for CT transformation did not differ significantly for the three HS^- treated iron oxides, but the rate of CT transformation by bisulfide-treated kaolinite was significantly lower, most likely due to kaolinite's lower iron content. The yield of chloroform (CF) from CT transformation was typically ∼1%. There was negligible or only slight adsorption of several natural organic matter (NOM) model compounds to the surface of HS^- treated goethite, and these compounds had no influence on CT transformation rate constants or CF yields. Juglone, on the other hand, adsorbed to a greater extent, and also significantly influenced the CF yield, increasing it by a factor of approximately 20 for HS^- treated hematite. We speculate that juglone or its HS^- addition product adsorbed to the mineral surface and acted as a hydrogen atom donor that reacted with the trichloromethyl radical intermediate, increasing the CF yield.