Byproduct Formation During the Reduction of TCE by Zero‐Valence Iron and Palladized Iron

Liang, Liyuan; Korte, Nic; Goodlaxson, J.D.; Clausen, Jay L.; Fernaǹdo, Quintus; Muftikian, Rosy

doi:10.1111/j.1745-6592.1997.tb01191.x

Cited by 63 publications

(56 citation statements)

References 7 publications

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“…Reductive dechlorination of chlorinated solvents by iron was first reported by Sweeny (1). Later, Gillham and others proposed exploiting these reactions for in situ remediation of groundwater contaminated by chlorinated solvents (2,3,4,5). Although reaction rates and reaction byproducts of most one and two carbon chlorinated compounds with iron have been measured, little is known about the reaction mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Understanding Trichloroethylene Chemisorption to Iron Surfaces Using Density Functional Theory

Zhang

Luo

Blowers

et al. 2008

Environ. Sci. Technol.

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This research investigated the thermodynamic favorability and resulting structures for chemical adsorption of trichloroethylene (TCE) to metallic iron using periodic density functional theory (DFT). Three initial TCE positions having the plane defined by HCC atoms parallel to the iron surface resulted in formation of three different chemisorption complexes between carbon atoms in TCE and the iron surface. The Cl-bridge initial configuration with the HCC plane of the TCE molecule perpendicular to the iron surface did not result in C-Fe bond formation. The most energetically favorable complex formed at the C-bridge site where the initial configuration had the C=C bond in TCE at a bridge site between adjacent iron atoms. In the C-bridge complex one C atom formed two sigma bonds to different Fe atoms while the second C atom formed a sigma bond with a second Fe atom. Surface complexation at the C-bridge site resulted in scission of all three C-Cl bonds, and also resulted in a shortening of the C=C bond to a distance intermediate between a double and a triple bond. Initial configurations with the C=C bond adsorbed at top or hollow sites on the iron surface resulted in formation of C-Fe sigma bonds between a single C and two adjacent Fe atoms, and the scission of only two C-Cl bonds. Bond angles and bond lengths indicated that there were no changes in bond order of the C=C bond for top and hollow adsorption. Chemisorption at the C-bridge site had an early transition state in which all three C-Cl bonds were activated from ~1.7 to ~2.2 Å, with an activation energy of 49 kJ/mol. The early transition state and the loss of all three Cl atoms upon chemisorption are consistent with most experimental observations that TCE undergoes complete dechlorination in one interaction with the iron surface. The absence of chemisorption and scission of only two C-Cl bonds at the Cl-bridge site is consistent with experimental observations that trace amounts of chloroacetylene may also be produced from reactions of TCE with iron.

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Section: Introductionmentioning

confidence: 99%

Understanding Trichloroethylene Chemisorption to Iron Surfaces Using Density Functional Theory

Zhang

Luo

Blowers

et al. 2008

Environ. Sci. Technol.

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“…Production and accumulation of chlorinated byproducts due to the low reactivity of iron powders towards lightly chlorinated hydrocarbons. For example, reduction of PCE and TCE by zerovalent iron has been observed to produce cis-1,2-DCE and VC [12,13]. Both compounds are of considerable toxicological concern.…”

Section: Introductionmentioning

confidence: 99%

Treatment of chlorinated organic contaminants with nanoscale bimetallic particles

1998

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“…As such, degradation rates vary among Fe filings obtained fiom different sources as a result of differences in surface characteristics such as specific surface area; surface chemical composition, and extent of surface oxidation (Gillham and O'Hannesin 1994;Horney et al 1995;Liang et al 1997). Laboratory studies have suggested that single step is unlikely and that stepwise dechlorination must take place on the metal surface (O'Hannesin 1993; Gillham and O'Hannesin 1994;Matheson and Tratnyek 1994;Sivavec and Horney 1995;Liang et al 1995;Pds et al 1995).…”

Section: Dechlorination Of Chlorinated Solvents By Zero-valence Iron mentioning

confidence: 99%

“…In collaboration with the UofA, researchers in the Environmental Sciences Division at O W L found that a bimetallic preparation of Fe with a small amount i complete dechlorination (for example: fiom TCE to ethylene or ethane) in a 3 -2 of palladium (Pd) (nominally 0.05% by weight) was a superior reductant for TCE (Korte et al 1995b(Korte et al , 1997bMuftikian et al 1995;Liang et al 1997;Grittini et al 1996). The bimetallic system yielded dechlorination kinetics that were one to two orders of magnitude faster than those for zero-valence iron alone.…”

Section: Dechlorination Of Chlorinated Solvents By Zero-valence Iron mentioning

confidence: 99%

In situ treatment of mixed contaminants in groundwater: Application of zero-valence iron and palladized iron for treatment of groundwater contaminated with trichloroethene and technetium-99

Korte¹,

Muck²,

Zutman³

et al. 1997

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1This report has been reproduced directly from the best available copy. 4-7(a) Binding energies of the Pd 3d3,2 and the Pd3d, peaks in the x-ray photoelectron spectrum of elemental Pd deposited on the iron surf-ace. 4.8. 4.9.5.1. 5.2.5.3.6.1. 7-4Tc (pCi/g) distribution in Fe columns 580,000 gal of water treated . . . 7-6 Number of times influent TCE concentration was reduced by % as it passed through the Pd/Fe treatment columns. Laboratory research conducted at ORNL and the UofA led to the discovery that zero-valence iron treated with a trace of palladium (pd) (nominally 0.05%) rapidly dechlorinated a wide range of hydrocarbons. Other research at ORNL and elsewhere has shown that many metals and radionuclides either precipitate or are adsorbed by zero-valence iron. Technetium (Tc) is particularly amenable to treatment of this type. Consequently, a combined approach using zero-valence iron for Tc and palladized iron (Pd/Fe) for trichloroethene (TCE) was applied to a groundwater waste stream at the PORTS facility.Laboratory research preparatory to the field tests demonstrated that Pd/Fe dechlorinated TCE one to two orders of magnitude faster than untreated iron. Further studies examined the nature of the Pd/Fe surface and evaluated the reaction mechanism. Work with x-ray photoelectron spectroscopy demonstrated that Pd attaches to the iron surface in a two-step process whereby a Pd-oxygen bond forms first with Pd in the +2 oxidation state. The Pd is then rapidly fbrther reduced to the elemental state as it plates on the Fe surface.Mechanistic studies have demonstrated that Pd/Fe reduces chlorinated hydrocarbons by hydrogenation. Hydrogen gas, formed because of the corrosion of Fe, is absorbed by the Pd. The chlorinated hydrocarbon adsorbs to the iron and is then reduced by hydrogen at the Pd/Fe interface.Laboratory studies with zero-valence iron revealed a very high capacity for immobilization of Tc. In a column study, approximately an order of magnitude more Tccontaminated water could be treated by the iron as compared to a conventional ion xiii exchange resin. The primary removal mechanism is believed to be reductive precipitation.In the field test, approximately 600,000 gal of water were treated. Treatment was straightfonvard and completely effective for Tc. The influent concentration of Tc was lower than anticipated (<20 pCi/L). Nevertheless, all of the Tc contained in the treated water was adsorbed by approximately 12 in. of a coarse zero-valence iron.

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Byproduct Formation During the Reduction of TCE by Zero‐Valence Iron and Palladized Iron

Cited by 63 publications

References 7 publications

Understanding Trichloroethylene Chemisorption to Iron Surfaces Using Density Functional Theory

Understanding Trichloroethylene Chemisorption to Iron Surfaces Using Density Functional Theory

Treatment of chlorinated organic contaminants with nanoscale bimetallic particles

In situ treatment of mixed contaminants in groundwater: Application of zero-valence iron and palladized iron for treatment of groundwater contaminated with trichloroethene and technetium-99

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