Degradation of carbon tetrachloride by iron metal: Complexation effects on the oxide surface

Timothy L. Johnson, William Fish, Yuri A. Gorby, Paul G. Tratnyek

Research output: Contribution to journalArticle

155 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)379-398
Number of pages20
JournalJournal of contaminant hydrology
Volume29
Issue number4
DOIs
StatePublished - Mar 1 1998

Keywords

  • Corrosion
  • Dechlorination
  • Groundwater remediation
  • Iron oxide
  • Passive film

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology

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