Abiotic Reductive Dechlorination of Chlorinated Ethylenes by Iron-Bearing Soil Minerals. 2. Green Rust

Abiotic reductive dechlorination of chlorinated ethylenes by the sulfate form of green rust (GRSO4) was examined in batch reactors. Dechlorination kinetics were described by a modified Langmuir−Hinshelwood model. The rate constant for reductive dechlorination of chlorinated ethylenes at reactive GRSO4 surfaces was in the range of 0.592 (±4.4%) to 1.59 (±6.3%) day-1. The specific reductive capacity of GRSO4 for target organics was in the range of 9.86 (±10.1%) to 18.0 (±4.3%) μM/g and sorption coefficient was in the range of 0.53 (±2.4%) to 1.22 (±4.3%) mM-1. Surface area-normalized pseudo-first-order initial rate constants for chlorinated ethylenes by GRSO4 were 3.4 to 8.2 times greater than those by pyrite. Chlorinated ethylenes were mainly transformed to acetylene, and no detectable amounts of chlorinated intermediates were observed. The rate constants for the reductive dechlorination of trichloroethylene (TCE) increased as pH increased (6.8 to 10.1) but were independent of solid concentration and initial TCE concentration. Magnetite and/or maghemite were produced by the oxidation of GRSO4 by TCE. These findings are relevant to the understanding of the role of abiotic reductive dechlorination during natural attenuation in environments that contain GRSO4.