Gas phase reduction of chlorinated VOCs by zero valent iron

The removal of trichloroethylene (TCE) by reduction with elemental iron was examined in batch reactors representing three phase gaseous systems (Fe-0 (solid), water vapor + TCE vapor + air mixture (gaseous), and condensed wat er on Fe-0 surface (aqueous)) and two phase aqueous systems (Fe-0 (solid), water (aqueous)) as the reaction medium. Two separate removal mechanisms we re found for TCE removal in the gas phase reactors: (1) adsorption onto the Fe-0 surface under low relative humidity (RH), and (2) reaction with Fe-0 to form other organic compounds, such as ethylene, isomers of dichloroethyl ene, and vinyl chloride under 100% RH conditions in the gas phase. The adso rption of TCE vapor onto the Fe-0 surface was fast initially and highest at low temperatures. The reduction reaction of TCE in the gas phase was first order with respect to the TCE concentration remaining in the gas phase und er conditions of 100% RH at 15, 22, and 35 degreesC, and the observed react ion rate constant (k(obs)) exhibited a maximum at elevated temperatures. Th e estimated k(obs) values for the degradation of dissolved TCE in aqueous s ystems were the same order of magnitude with the rate constants in the gas phase and exhibited an increasing rate at higher temperatures. The results suggest that Fe-0 represents an economical choice for vapor phase barriers to limit the spread of contaminants in soil gas and reduce fugitive air emi ssions from contaminated sites.