Overcoming Barriers to the Remediation of Carbon Tetrachloride through Manipulation of Competing Reaction Mechanisms--Final Technical Report

Tratnyek, Paul G. ; Amonette, James E. ; Bylaska, Eric J.

Oregon Health & Science University

关键词: Surface Area Carbon Tetrachloride, Chloroform, Groundwater, Remediation, In Situ Chemical Reduction, Dechlorination, Zerovalent Iron Metal, Nanoparticles;    Capacity;    Diagnosis;    Chloroform;    Carbon Tetrachloride, Chloroform, Groundwater, Remediation, In Situ Chemical Reduction, Dechlorination, Zerovalent Iron Metal, Nanoparticles;   

DOI  :  10.2172/900346
RP-ID  :  ER63485-F
RP-ID  :  FG07-02ER63485
RP-ID  :  900346

美国|英语

来源: UNT Digital Library

【 摘 要 】

The premise of this project was that if we understood the fundamental chemistry that controls the branching among product formation pathways for the degradation of CCl4, we could design remediation strategies that minimize the formation of CHCl3 and thereby provide badly needed alternatives for remediation of the large plumes of CCl4 that contaminate several DOE sites. To this end, we performed a series of coordinated batch, spectroscopic, and modeling experiments, to study the effect of a variety of factors on the yield of CHCl3 from CCl4 during reduction with zero-valent iron (Fe0). The factors studied include those with direct implications for field performance (e.g., the concentration of CCl4 relative to the amount of iron surface area) and others chosen for diagnosis of the reaction mechanism (e.g., incorporation of deuterium into CCl4 reduction products in the presence of D2O). The key mechanistic findings of this study are (i) that CCl3• probably is not an intermediate in the formation of CF, but CCl3− probably is, (ii) the high reductive capacity of the Fe0 core favors the concerted 2e− reduction, and (iii) magnetite on Fe0 favors the benign product formation pathway. The latter conclusion is based on the observation that one type of nano-sized Fe0 that is coated with magnetite shell produces low yields of chloroform (0-40%), whereas others produce the higher yields of chloroform (60-100%) that are typical of most methods for reducing CCl4 (including biodegradation). Since nano-Fe0 can, in principle, be introduced into the deep subsurface by injection, our results would suggest that the right type of nano-Fe0 introduced in the right way might be highly effective at dechlorinating CCl4 with minimal formation of CHCl3 or other undesirable by-products. This conclusion may offer a breakthrough in the search for remediation technologies that are suitable for the deep CCl4-contamination at DOE sites such as the 200-W area of Hanford.