Effects of surface oxidation and oxygen on the removal of trichloroethylene from the gas phase using elemental iron

Abstract

The reduction of trichloroethylene (TCE) in the gas phase by Fedegrees was examined under water vapor saturated conditions (relative humidity (RH) = 100%). The reaction conformed to first-order rate kinetics under anaerobic (N-2 atmosphere) conditions and acid-washed Fedegrees exhibited a faster TCE removal rate than unamended (partially oxidized) Fedegrees, i.e., k(obs) = 0.015 h(-1) versus 0.012 h(-1). Analysis of the two types of Fedegrees showed that 40.3% of the unamended Fedegrees surface was nonreactive. Experiments with iron oxides, which form commonly on the surface of Fedegrees exposed to humid air (magnetite and maghemite), showed that these solids were nonreactive with TCE under anaerobic conditions. Under aerobic conditions (air), TCE reduction occurred in two distinct phases. There was a fast initial rate followed by a slower later rate of reduction when the oxide layer was formed. Further experiments showed that the Fedegrees surface was saturated with TCE at higher concentrations (K-1/2 = 5,397.4 +/- 345.4 ppmv) and that oxygen acted as an irreversible inhibitor of TCE reduction (maximum rate of reaction decreased when oxygen was present).