reduction for highly chlorinated compounds like HCA and PCA for chlorinated
ethanes (O’Loughlin and Burris 2004) or PCE and TCE for chlorinated ethylenes
(Lee and Batchelor 2002a). However, Huang et al. (2018) report that only small
molecules can be transported through the interlayer of the layered double hydroxide
structure. Other minerals, e.g., iron sulfide (FeS), pyrrhotite (Fe 1Àx 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 (Butler and 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).
Among all the reactants containing iron, ZVI is the prime example of an electrochemical redox system that have been implemented to intercept and remediate
(1) COCs by funnel-and-gate system and (2) overlapping plumes of COCs by iron
barrier (Zhang 2003; Wilkin et al. 2003). After 4 years of operations, ZVI appears as
a long-term sink for carbon, sulfur, calcium, silicon, nitrogen, and magnesium
(Wilkin et al. 2003). Moreover, and in agreement with the literature, consistent
patterns of spatially variable mineral precipitation and microbial activity have been
observed during the treatment. Also, while pore space has been lost and due to the
accumulation of endogenic components, no pervasive pore clogging was evidenced
(Wilkin et al. 2003).
For these reasons, this chapter focuses on the development and the improvement
of ZVI particles application for the chemical reduction of COCs.
6.3.2 Zero-Valent Iron
6.3.2.1 History, Reactivity, and Characterization
Zero-valent iron (ZVI) particles have been considered in the late 1970s for the
remediation of COCs (Sweeny 1980) and was first applied for in situ remediation
in the 1990s as granular iron in permeable reactive barriers (PRBs) (Gillham and
O’Hannesin 1994; O’Hannesin and Gillham 1998; Obiri-Nyarko et al. 2014). One of
the first studies concerning in situ remediation of polyhalogenated hydrocarbons
with zero-valent metals has been reported by Tratnyek et al. (2003). Since then,
several sites have been cleaned up using ZVI, and remediation yields of 90% were
achieved within a few weeks (Brown 2010).
Three reactions were proposed to explain degradation mechanisms: the direct
reduction on ZVI surface (Eq. 6.28), the reduction by ferrous iron Fe
2+ species
(Eq. 6.30), and by hydrogen H 2 (hydrogenation reactions, Eq. 6.31), both produced
during anaerobic corrosion of iron (Eq. 6.29) (Matheson and Tratnyek 1994).
However, reduction by dissolved Fe
2+ is quite slow and reduction by H 2 requires
an effective catalyst.
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
303
ethanes (O’Loughlin and Burris 2004) or PCE and TCE for chlorinated ethylenes
(Lee and Batchelor 2002a). However, Huang et al. (2018) report that only small
molecules can be transported through the interlayer of the layered double hydroxide
structure. Other minerals, e.g., iron sulfide (FeS), pyrrhotite (Fe 1Àx 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 (Butler and 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).
Among all the reactants containing iron, ZVI is the prime example of an electrochemical redox system that have been implemented to intercept and remediate
(1) COCs by funnel-and-gate system and (2) overlapping plumes of COCs by iron
barrier (Zhang 2003; Wilkin et al. 2003). After 4 years of operations, ZVI appears as
a long-term sink for carbon, sulfur, calcium, silicon, nitrogen, and magnesium
(Wilkin et al. 2003). Moreover, and in agreement with the literature, consistent
patterns of spatially variable mineral precipitation and microbial activity have been
observed during the treatment. Also, while pore space has been lost and due to the
accumulation of endogenic components, no pervasive pore clogging was evidenced
(Wilkin et al. 2003).
For these reasons, this chapter focuses on the development and the improvement
of ZVI particles application for the chemical reduction of COCs.
6.3.2 Zero-Valent Iron
6.3.2.1 History, Reactivity, and Characterization
Zero-valent iron (ZVI) particles have been considered in the late 1970s for the
remediation of COCs (Sweeny 1980) and was first applied for in situ remediation
in the 1990s as granular iron in permeable reactive barriers (PRBs) (Gillham and
O’Hannesin 1994; O’Hannesin and Gillham 1998; Obiri-Nyarko et al. 2014). One of
the first studies concerning in situ remediation of polyhalogenated hydrocarbons
with zero-valent metals has been reported by Tratnyek et al. (2003). Since then,
several sites have been cleaned up using ZVI, and remediation yields of 90% were
achieved within a few weeks (Brown 2010).
Three reactions were proposed to explain degradation mechanisms: the direct
reduction on ZVI surface (Eq. 6.28), the reduction by ferrous iron Fe
2+ species
(Eq. 6.30), and by hydrogen H 2 (hydrogenation reactions, Eq. 6.31), both produced
during anaerobic corrosion of iron (Eq. 6.29) (Matheson and Tratnyek 1994).
However, reduction by dissolved Fe
2+ is quite slow and reduction by H 2 requires
an effective catalyst.
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
303