Interaction of Chloroethanes and Chloroethenes with Unrusted and Rusted High Carbon Iron Filings

Abstract

Reductive dehalogenation of several chloroethanes, viz., 1,1,1-trichloroethane (1,1,1-TCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1-dichloroethane (1,1-DCA), 1,2-dichloroethane (1,2-DCA), and chloroethenes, viz., 1,1-dichloroethene (1,1-DCE), cis-1,2-dichloroethene (cis-1,2-DCE), and trans-1,2-dichloroethene (trans-1,2-DCE) by unrusted and rusted high carbon iron filings (HCIF) was studied. None of the above compounds adsorbed appreciably on the HCIF surface. 1,2-DCA and cis-1,2-DCE were not appreciably dehalogenated by either unrusted (HCIF-1) or rusted (HCIF-2) HCIF. In all other cases, the dehalogenation rates could be described using pseudo-first-order kinetics. Pseudo-first-order dehalogenation rates with HCIF-1 were considerably higher than the corresponding rates with HCIF-2 in all cases. This suggested that gradual rusting of HCIF used in continuous systems such as permeable reactive barriers was likely to adversely affect the long-term dehalogenation rate of the above compounds. Reduction in dehalogenation rates was more for compounds like 1,1,2-TCA (half-life [t_1/2] increased from 6 to 92 hours) and trans-1,2-DCE (t_1/2 increased from 10.7 to 89.7 hours), which dehalogenated predominantly by the reductive α-elimination mechanism during interaction with HCIF, as compared to compounds like 1,1,1-TCA (t_1/2 increased from 1.7 to 9.4 hours), 1,1-DCA (t_1/2 increased from 184 to 388 hours), and 1,1-DCE (t_1/2 increased from 84 to 210 hours), which dehalogenated predominantly by the reductive β-elimination mechanism.