Aqueous oxidation of trichloroethene (TCE): a kinetic and thermodynamic analysis

摘要

An empirical kinetic rate law was determined for the aqueous oxidation of trichloroethene (TCE). By measuring both the rate of disappearance of TCE and the rate of appearance of carbon dioxide and chloride ion, mass balances were monitored to confirm that 'mineralization' was the ultimate reaction. Dilute buffer solutions were used to fix pH and stoichiometrically sufficient amounts of dissolved oxygen were used to make the reactions zero-order in oxygen. Using standard chemical kinetic methods, two orders of magnitude were spanned in initial TCE concentration and used in the resulting double-log plot vs. initial rate (regressed using both linear and polynomial fits) to determine the rate constant and 'true' reaction order (i.e., with respect to concentration, not time). By determining rate constants over the temperature interval 343-373K, an Arrhenius activation energy was determined for the reaction. A study was made of the potential effect of buffer ligand concentration and type (phosphate, borate, acetate, carbonate, sulfate), ionic strength, specific electrolytes, and pH on the rate of TCE. The aqueous oxidation reaction rate was found to be pH dependent over the pH range pH 2 to pH 1O and strongly inhibited by high dissolved bromide concentration. The equilibrium aqueous solubilities of TCE was determined by making reversed measurements from 294-390K. Together with the kinetic rate law, the thermodynamic data are required to develop in situ thermal remedial techniques for TCE and to model the reactive transport behavior of TCE in the subsurface.