Reductive Dechlorination of DNAPL Trichloroethylene by Zero-Valent Iron

Abstract

The reduction of trichloroethyl (TCE) by metallic iron was studied under conditions in which the trichloroethylene would exist as a separate phase in a water/iron system. The products of the reaction were determined over time using gas chromatography (GC) and mass spectrometry (MS). The kinetics of the loss of TCE and the formation of chloride were determined to follow zero-order kinetics under these conditions with zero-order rate constants of 4.8 × 10−3 mg TCI h−1 g−1 iron and 3.8 × 10−3 mg Cl− h−1 g−1 iron. The zero-order rate constant was observed to depend on the mass of iron present. The reaction was carried out in deuterium oxide to compare the reaction pathways suggested in the literature for solution reduction of TCE. It was observed that the major product was acetylene with minor components of ethane and ethene. The deuterium oxide showed that the ethene and ethane were composed of a 68% totally deuterated ethene and 32% ethene containing only one hydrogen. No deuterium was evident when acetylene formed in the deuterium oxide system, indicating that all of the hydrogen in the dense nonaqueous phase liquid (DNAPL) arises from TCE. The result of this study indicates that metallic iron can dechlorinate DNAPL TCE.