Fast Dechlorination of Chlorinated Ethylenes by Green Rust in the Presence of Bone Char

Layered iron­(II)–iron­(III) hydroxides [green rusts (GRs)] constitute fast reductants for chlorinated methanes, but most studies of the reaction of GRs with chlorinated ethylenes (CEs) have reported little or no reduction. In this work, we demonstrate that bone char (BC) can eliminate the kinetic hindrance of dehalogenation of CEs by GR. Dechlorination of perchloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene, and trans-dichloroethylene (∼10 μM in aqueous phase) by GR/BC mixtures (∼3.2 g/L GR and 0.15 g/L BC) followed pseudo-first-order kinetics with half-lives of 3.15, 3.01, 7.97, and 0.63 h, respectively, with acetylene as the main product (>85%), while no reaction took place in the absence of BC or GR. The rate of TCE removal was almost independent of GR concentration but increased linearly with BC concentration, indicating that the reactive sites for dechlorination are on the BC phase. GR could directly reduce BC in amounts of ≤0.21 mmol of e–/g, suggesting that CEs were dechlorinated by reduced functional groups on BC that functions as an electron mediator with GR acting as the “bulk” reductant. The GR/BC mixture exhibited a similar rate of removal of PCE and TCE in contaminated groundwater and in the laboratory-spiked solutions. This opens new perspectives for both in situ remediation and natural attenuation of CEs in anoxic, neutral, and alkaline iron-rich contaminated sediments and aquifers.