Abiotic reductive dechlorination of cis-DCE by ferrous monosulfide mackinawite

Abstract

Cis-1,2,-dichloroethylene (cis-DCE) is a toxic, persistent contaminant occurring mainly as a daughter product of incomplete degradation of perchloroethylene (PCE) and trichloroethylene (TCE). This paper reports on abiotic reductive dechlorination of cis-DCE by mackinawite (FeS1-x), a ferrous monosulfide, under variable geochemical conditions. To assess in situ abiotic cis-DCE dechlorination by mackinawite in the field, mackinawite suspensions prepared in a field groundwater sample collected from a cis-DCE contaminated field site were used for dechlorination experiments. The effects of geochemical variables on the dechlorination rates were monitored. A set of dechlorination experiments were also carried out in the presence of aquifer sediment from the site over a range of pH conditions to better simulate the actual field situations. The results showed that the suspensions of freshly prepared mackinawite reductively transformed cis-DCE to acetylene, whereas the conventionally prepared powder form of mackinawite had practically no reactivity with cis-DCE under the same experimental conditions. Significant cis-DCE degradation by mackinawite has not been reported prior to this study, although mackinawite has been shown to reductively transform PCE and TCE. This study suggests feasibility of using mackinawite for in situ remediation of cis-DCE-contaminated sites with high S levels such as estuaries under naturally achieved or stimulated sulfate-reducing conditions.

Effects of Sulfate Reduction on Trichloroethene Dechlorination by Dehalococcoides-Containing Microbial Communities

“…At remediation sites, sulfate reduction can overlap with iron reduction, which can lead to precipitated iron sulfide. The biogenic iron sulfide may reduce part of the sulfide toxicity and also perform abiotic chloroethene degradation when electron donor is in excess (43,44). The overall TCE remediation may benefit from the resulting iron sulfide formation.…”

Fe(II) Redox Chemistry in the Environment

“…The physicochemical properties of FeS influence its reductive reactivity. FeS is a metallic conductor with delocalized Fe 3 d electrons, which is thought to partially explain its effectiveness as a reductant. , This is why the orientation of FeS layers perpendicular to the iron surface is found to enhance the reductive reactivity. , The particle size of FeS also influences its reactivity, with nanosize FeS shown to be more reactive than macrosize FeS, due to a higher surface area and more available reactive sites . Indeed, one reason that freeze-dried FeS is less reactive than nonfreeze-dried FeS , is attributed to particle aggregation during the drying process, which increases its particle size and lowers its reactivity. , Many polymeric stabilizers (e.g., carboxymethyl cellulose) have been employed to stabilize FeS to improve its reactivity. ,, In addition, nanosize FeS containing various structural flaws , contributes to a higher reactivity compared with macrosize FeS.…”

“…On the other hand, the addition of 2,2′-bipyridine and 1,10-phenanthrolene resulted in enhanced degradation of hexachloroethane, which was attributed to the participation of delocalized π* molecular orbitals in the electron-transfer reaction . The addition of citrate enhanced the reductive reactivity of FeS, likely due to the inhibition of the passivation layer on the FeS surface or the formation of surface reactive groups facilitating the reaction …”

In Situ Chemical Reduction of Chlorinated Organic Compounds

“…Other minerals, e.g. iron sulfide FeS, pyrrhotite Fe 1-x S, mackinawite Fe 1+x S, pyrite FeS 2 , and magnetite Fe 3 O 4 , which are present in anaerobic environments, have been shown to contribute to the reductive dechlorination of chlorinated ethylenes under specific conditions Hayes 1998, 2000;Weerasooriya and Dharmasena 2001;Lee and Batchelor 2002b;Jeong et al 2007;Hyun and Hayes 2015;Gong et al 2016;Yang et al 2017;Culpepper et al 2018). Among all the reactants containing iron, ZVI is the prime example of an electrochemical redox system that have been implemented to intercept and remediate (i) COCs by funnel-and-gate system and (ii) overlapping plumes of COCs by iron barrier (Zhang 2003;Wilkin et al 2003).…”