TY - JOUR
T1 - Degradation of carbon tetrachloride by iron metal
T2 - Complexation effects on the oxide surface
AU - Johnson, Timothy L.
AU - Fish, William
AU - Gorby, Yuri A.
AU - Tratnyek, Paul G.
N1 - Funding Information:
Most experimental work was performed at the Battelle Pacific Northwest National Laboratories, Richland, WA, while T.L. Johnson was supported by an Energy Research Fellowship from the DOE. Other portions were supported by the University Consortium Solvents-In-Groundwater Research Program, the National Science Foundation through Award BCS-9212059, and the Petroleum Research Fund through award 29995-AC5. E.J. Reardon contributed through early discussions and speciation modeling, and J.C. Westall provided additional review of the manuscript.
PY - 1998/3/1
Y1 - 1998/3/1
N2 - Dehalogenation of chlorinated aliphatic contaminants at the surface of zero-valent iron metal (Fe0) is mediated by the thin film of iron (hydr)oxides found on Fe0 under environmental conditions. To evaluate the role this oxide film plays in the reduction of chlorinated methanes, carbon tetrachloride (CC14) degradation by Fe0 was studied under the influence of various anions, ligands, and initial CC14 concentrations ([ρ]0). Over the range of conditions examined in these batch experiments, the reaction kinetics could be characterized by surface-area-normalized rate constants that were pseudo-first order for CC14 disappearance (k(CC14)) and zero order for the appearance of dissolved Fe2+ (k(Fe2+)). The rate of dechlorination exhibits saturation kinetics with respect to [ρ]0, suggesting that CC14 is transformed at a limited number of reactive surface sites. Because oxidation of Fe0 by CC14 is the major corrosion reaction in these systems, k(Fe2+) also approaches a limiting value at high CC14 concentrations. The adsorption of borate strongly inhibited reduction of CC14, but a concomitant addition of chloride partially offset this effect by destabilizing the film. Redox active ligands (catechol and ascorbate) and those that are not redox active (EDTA and acetate), all decreased k(CC14) (and (kFe2+)). Thus, it appears that the relatively strong complexation of these ligands at the oxide-electrolyte interface blocks the sites where weak interactions with the metal oxide lead to dehalogenation of chlorinated aliphatic compounds.
AB - Dehalogenation of chlorinated aliphatic contaminants at the surface of zero-valent iron metal (Fe0) is mediated by the thin film of iron (hydr)oxides found on Fe0 under environmental conditions. To evaluate the role this oxide film plays in the reduction of chlorinated methanes, carbon tetrachloride (CC14) degradation by Fe0 was studied under the influence of various anions, ligands, and initial CC14 concentrations ([ρ]0). Over the range of conditions examined in these batch experiments, the reaction kinetics could be characterized by surface-area-normalized rate constants that were pseudo-first order for CC14 disappearance (k(CC14)) and zero order for the appearance of dissolved Fe2+ (k(Fe2+)). The rate of dechlorination exhibits saturation kinetics with respect to [ρ]0, suggesting that CC14 is transformed at a limited number of reactive surface sites. Because oxidation of Fe0 by CC14 is the major corrosion reaction in these systems, k(Fe2+) also approaches a limiting value at high CC14 concentrations. The adsorption of borate strongly inhibited reduction of CC14, but a concomitant addition of chloride partially offset this effect by destabilizing the film. Redox active ligands (catechol and ascorbate) and those that are not redox active (EDTA and acetate), all decreased k(CC14) (and (kFe2+)). Thus, it appears that the relatively strong complexation of these ligands at the oxide-electrolyte interface blocks the sites where weak interactions with the metal oxide lead to dehalogenation of chlorinated aliphatic compounds.
KW - Corrosion
KW - Dechlorination
KW - Groundwater remediation
KW - Iron oxide
KW - Passive film
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U2 - 10.1016/S0169-7722(97)00063-6
DO - 10.1016/S0169-7722(97)00063-6
M3 - Article
AN - SCOPUS:0032030747
SN - 0169-7722
VL - 29
SP - 379
EP - 398
JO - Journal of contaminant hydrology
JF - Journal of contaminant hydrology
IS - 4
ER -