Effects of Surface Oxidation and Oxygen on the Removal of Trichloroethylene From the Gas Phase Using Elemental Iron

The reduction of trichloroethylene (TCE) in the gas phase byFe° was examined under water vapor saturatedconditions (relative humidity (RH) = 100%). The reactionconformed to first-order rate kinetics under anaerobic(N₂ atmosphere) conditions and acid-washedFe°exhibited a faster TCE removal rate than unamended (partially oxidized) Fe°, i.e., k_obs = 0.015 h^-1 versus0.012 h^-1. Analysis of the two types of Fe° showedthat 40.3% of the unamended Fe° surface was nonreactive. Experiments with iron oxides, which form commonly on the surface of Fe° exposed to humid air (magnetiteand 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 fastinitial rate followed by a slower later rate of reduction when the oxide layer was formed. Further experiments showed that theFe° surface was saturated with TCE at higher concentrations (K_1/2 = 5,397.4 ± 345.4 ppmv) and thatoxygen acted as an irreversible inhibitor of TCE reduction(maximum rate of reaction decreased when oxygen was present).