Linear free-energy relationship analysis of the fate of chlorinated 1- and 2-carbon compounds by redox-manipulated smectite clay minerals.

This paper expands on earlier work on the effect of molecular structure on the fate of a series of chlorinated 1- and 2-carbon compounds (RCl), including carbon tetrachloride, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, hexachloroethane, trichloroethene, tetrachloroethene, trichloronitromethane, and trichloroacetonitrile, in the presence of unaltered (SWa-U) and reduced (SWa-R) ferruginous smectite. A linear free-energy relationships (LFERs) analysis was conducted to explain kinetic data for RCl adsorption and dechlorination. Correlation analyses based on RCl hydration energies, hydrolysis rate constants, or bond dissociation energies were significant (r2 > 0.87) for RCl adsorption by SWa-R but not so for RCl adsorption by SWa-U (r2 < 0.5). The most statistically significant relationships describing RCl kinetic data were achieved using multivariable regression analysis including RCl hydration energies (or hydrolysis rate constant) and bond dissociation energies for RCl heterolysis. The outcome of this study indicates that the oxidation state of structural Fe in the clay strongly influences RCl hydration. A mechanism consistent with the present LFERs analysis corresponds to RCl hydration as the limiting step for adsorption and dechlorination by redox-manipulated smectites.