Investigations of reductive dechlorination reactions of chlorinated ethenes and ethanes on zero-valent metals using compound specific isotopic analysis
By: by Nancy Anne VanStone.
Published: 2006
Language: eng
Number of pages: 213
ISBN-13: 9780494157541
Description: Reductive dechlorination reactions occurring on zero-valent metal surfaces for chlorinated ethenes and chlorinated ethanes are investigated using compound specific isotopic analysis (CSIA) to measure carbon isotopic fractionation and carbon kinetic isotope effects (KIE). Reductive dechlorination of chlorinated contaminants on zero-valent iron (Fe0) is used for remediation purposes at over 100 sites worldwide employing permeable reactive barrier (PRB) technology. Degradation can occur via 3 main pathways: (1) alpha-elimination, (2) beta-elimination and (3) hydrogenolysis. Experiments documenting carbon isotopic fractionation observed during degradation of a suite of chlorinated ethenes are described, and it is demonstrated that reproducible carbon isotopic fractionation occurs for perchloroethene (PCE), trichloroethene (TCE),  cis-dichloroethene (cis-DCE) and vinyl chloride (VC). The results for Fe0 from two different sources show distinct differences in both rates of reaction and isotopic fractionation factors (epsilon), particularly for the cis-DCE and VC. Using ground water samples from pre- and post-treatment of a Fe0 PRB at F. E. Warren Air Force Base, it is established that carbon isotopic fractionation of chlorinated ethenes follows the same principles under field conditions, and it is shown that CSIA, in combination with traditional compositional analysis, can help to resolve complex performance-related problems for PRBs. Finally, it is demonstrated that reaction pathways and mechanisms can be investigated using CSIA and ranges of epsilon and KIE are established for the investigated reactions on different zero-valent metals. In batch experiments monitoring dichloroethane (DCA) degradation on Zn0, CSIA was used to determine that a common rate limiting step occurs for hydrogenolysis and alpha-elimination reactions of 1,1-DCA. As well, overall epsilon and KIE are greater for beta-elimination of 1,2-DCA than for hydrogenolysis and alpha-elimination of 1,1-DCA. The degradation of a chlorinated ethene, cis-DCE, was investigated on Fe0. Direct measurements of epsilon and KIE for hydrogenolysis and beta-elimination were measured using CSIA. It is established that these reactions do not share a rate limiting step, and unique and reproducible carbon isotopic fractionation is associated with each reaction pathway. CSIA has been shown to be a versatile tool, aiding research as both a reliable diagnostic (i.e. identification of degradation) and as a valuable analytical instrument for mechanistic studies.
Notes: Source: Dissertation Abstracts International, Volume: 67-06, Section: B, page: 3144.

Thesis (Ph.D.)--University of Toronto, 2006.

Includes bibliographic references.

Electronic version licensed for access by U. of T. users.