| Corrosion of iron pipes leads to the release of ferrous iron, Fe(II), and the formation of iron oxides, such as goethite and magnetite, on the pipe surface in drinking water distribution systems. Such Fe(II)-bearing minerals can mediate the reduction of disinfection byproduct (DBPs), which are small, halogenated organic compounds.; Batch experiments were performed to investigate the kinetics and pathways of the degradation of six different chemical classes of DBPs in the presence of aqueous Fe(II), Fe(II)-bound to goethite and magnetite, magnetite, and carbonate green rust. Halonitromethanes and haloacetic acids were degraded via reduction, while halo acetonitriles, haloketones and haloacetaldehyde hydrates were transformed via both hydrolysis and reduction. Chloroform was unreactive with any of the corrosion products. DBP reduction kinetics were influenced by DBP chemical structure and identity of the reductant. Carbonate green rust had the greatest reactivity, followed by Fc(II) bound to goethite and magnetite, aqueous Fe(II), and structural Fe(II) present in magnetite. For DBPs of structure Cl3C-R, reduction rate constants correlated with the electron egativity of the -R group and with one electron reduction potential. In addition to chemical transformation, sorption onto the iron oxide minerals was also an important loss process for 1,1,1-trichloropropanone. These findings will facilitate the development of models for predicting the fate of these compounds in distribution systems.; To investigate the relationship between changes in reactivity and changes in the mineral surface, reductive degradation of 4-chloromtrobenzene and trichloronitromethane by Fe(II) bound to goethite was examined by performing sequential-spike batch experiments combined with material characterization (transmission electron microscopy and X-ray diffraction). Results demonstrate that the degradation reactions result in goethite growth in the c-direction and altered morphology of particle tips. These changes led to decreased reactivity, suggesting that the newly formed material is less reactive than the original goethite. The results presented here conclude that the reactive surface responsible for organic contaminant reduction is the (021) face on goethite. These results represent an important step towards elucidating the link between mineral surface changes and the evolving kinetics of contaminant degradation at the mineral-water interface. |
