Dept. of Environmental and Biomolecular Systems
Oregon Health & Science University
Carbon tetrachloride (CT), and 1,2,3-trichloropropane (TCP)-two chlorinated aliphatic compounds that have very different susceptibilities to dechlorination-were studied for their reactivity via different abiotic pathways. Batch experiments performed with CT involved reduction by Fe[superscript 0], which produced chloroform as the major product via hydrogenolysis. The yield of chloroform-Y[subscript CF], which is a parameter that we want to minimize-was found to be dependent on the nature of the surface, and was low when the surface contained magnetite. Based on results from batch experiments with nano-Fe[superscript 0] with a magnetite shell (Fe[superscript H2]), we proposed an alternate pathway for CT dechlorination where CCl[subscript 3] [superscript _] is formed by a concerted 2e[superscript _] reduction (with simultaneous dissociation of a C-Cl bond), without CCl[subscript 3][superscript.] being formed as an intermediate. We concluded that conditions that can force CCl[subscript 3][superscript _]to go to the carbene versus into solution, will help lower Y[subscript CF]. Other batch experiments studying kinetics of CT dechlorination indicated that nano-Fe[superscript 0] is not faster than larger iron on a surface-area normalized basis. We investigated the aging of Fe[superscript H2] in water-which is one of the most important uncertainties associated with the use of iron nanoparticles for remediation-by various analytical techniques including XRD, TEM, CT reaction kinetics, electrochemistry, etc. Our results show evidence for rapid destruction of the original Fe(III) oxide film on Fe[superscript H2] during immersion (0-2 days)and the subsequent formation of a new mixed-valence Fe(II)-Fe(III) oxide shell. Batch experiments with TCP were performed under all possible abiotic degradation pathways. TCP is more recalcitrant than CT towards remediation by oxidation-reduction processes, and exhibits little or no reaction with common reductants, such as Fe[subscript 0]. It does, however, react at measurable rates with some unaged dry Fe[superscript H2], palladized nano-Fe[superscript 0], and zinc. TCP can also be significantly (but slowly) degraded via hydrolysis at high pH and temperatures. Oxidation of TCP is much more feasible than reduction, especially when involving strong free-radical intermediates like hydroxyl radical (in activated hydrogen peroxide) and sulfate radical (in activated persulfate). Activated persulfate, in particular, not only quickly oxidizes, but also completely dechlorinates TCP, and may be among the most viable options for field applications.
OGI School of Science and Engineering
Sarathy, Vaishnavi, "Engineered remediation and natural attenuation of halogenated alkanes (carbon tetrachloride and 1,2,3-trichloropropane) a study of contaminant reactivity and reductant morphology" (2008). Scholar Archive. 331.