Tl. Johnson et al., DEGRADATION OF CARBON-TETRACHLORIDE BY IRON METAL - COMPLEXATION EFFECTS ON THE OXIDE SURFACE, Journal of contaminant hydrology, 29(4), 1998, pp. 379-398
Citations number
74
Categorie Soggetti
Water Resources","Environmental Sciences","Geosciences, Interdisciplinary
Dehalogenation of chlorinated aliphatic contaminants at the surface of
zero-valent iron metal (Fe-0) is mediated by the thin film of iron (h
ydr)oxides found on Fe-0 under environmental conditions. To evaluate t
he role this oxide film plays in the reduction of chlorinated methanes
, carbon tetrachloride (CCl4) degradation by Fe-0 was studied under th
e influence of various anions, ligands, and initial CCl4 concentration
s ([P](0)). Over the range of conditions examined in these batch exper
iments, the reaction kinetics could be characterized by surface-area-n
ormalized rate constants that were pseudo-first order for CCl4 disappe
arance (k(CCl4)), and zero order for the appearance of dissolved Fe2(k(Fe2+)). The rate of dechlorination exhibits saturation kinetics wit
h respect to [P](0), suggesting that CCl4 is transformed at a limited
number of reactive surface sites. Because oxidation of Fe-0 by CCl4 is
the major corrosion reaction in these systems, k(Fe2+) also approache
s a limiting value at high CCl4 concentrations. The adsorption of bera
te strongly inhibited reduction of CCl4, but a concomitant addition of
chloride partially offset this effect by destabilizing the film. Redo
x active ligands (catechol and ascorbate), and those that are not redo
x active (EDTA and acetate), all decreased k(CCl4) (and k(Fe2+)). Thus
, it appears that the relatively strong complexation of these Ligands
at the oxide-electrolyte interface blocks the sites where weak interac
tions with the metal oxide lead to dehalogenation of chlorinated aliph
atic compounds. (C) 1998 Elsevier Science B.V.