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

关键词: BIODEGRADATION;    CAPACITY;    CARBON TETRACHLORIDE;    CHEMISTRY;    CHLOROFORM;    DESIGN;    DEUTERIUM;    DIAGNOSIS;    IRON;    MAGNETITE;    PERFORMANCE;    PLUMES;    REACTION KINETICS;    SIMULATION;    SURFACE AREA Carbon Tetrachloride;    Chloroform;    Groundwater;   

DOI  :  10.2172/900346
RP-ID  :  ER63485-F
PID  :  OSTI ID: 900346
Others  :  TRN: US200717%%70

学科分类：环境科学（综合）

美国|英语

来源: SciTech Connect

【 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.