Reductive Dechlorination of Trichloroethylene and Carbon Tetrachloride at Iron Oxides and Basalt Minerals

Abiotic degradation of trichloroethylene (TCE) and carbon tetrachloride (CCl₄) in aqueous solutions in the presence of iron oxides, basalt, and its minerals was investigated. The objective of this work is to gain an understanding of chemical interactions of chlorinated solvents with basalt in order to aid remediation efforts. The basalt samples used in these studies were collected near the Idaho National Engineering and Environmental Laboratory. Additionally, basaltic minerals (plagioclase, olivine, augite, magnetite, and ilmenite) and iron oxides (FeO, Fe₂O₃, Fe₃O₄, FeTiO₃, FeOOH) were investigated. Reactivity studies were conducted in which these materials were exposed to 16 ppm aqueous solutions of TCE and CCl₄ under anaerobic conditions. The reaction products were monitored over time using solid phase microextraction coupled with gas chromatography. The results indicate that reductive dechlorination of TCE occurred at FeO and FeTiO₃ only. In contrast, reductive dechlorination of CCl₄ was observed when reacted with all Fe(II)-bearing materials. Degradation of the CCl₄ was significantly faster than the TCE when reacted under the same conditions (hours compared to days or weeks for FeTiO₃ and FeO). Additionally, dechlorination of CCl₄ was observed to occur at plagioclase which was unexpected since plagioclase cannot support reductive dechlorination.