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 (Fe0 (solid), water vapor + TCE vapor + air mixture (gaseous), and condensed water on Fe0 surface (aqueous)) and two phase aqueous systems (Fe0 (solid), water (aqueous)) as the reaction medium. Two separate removal mechanisms were found for TCE removal in the gas phase reactors: (1) adsorption onto the Fe0 surface under low relative humidity (RH), and (2) reaction with Fe0 to form other organic compounds, such as ethylene, isomers of dichloroethylene, and vinyl chloride under 100% RH conditions in the gas phase. The adsorption of TCE vapor onto the Fe0 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 under conditions of 100% RH at 15, 22, and 35 degrees C, and the observed reaction rate constant (kobs) exhibited a maximum at elevated temperatures. The estimated kobs values for the degradation of dissolved TCE in aqueous systems 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 Fe0 represents an economical choice for vapor phase barriers to limit the spread of contaminants in soil gas and reduce fugitive air emissions from contaminated sites.