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Abstract
Recent studies of contaminant reduction by zero-valent iron metal (Fe0) have highlighted
the role of iron oxides at the metal-water interface and the effect that sorption
has at the oxide-water interface on contaminant reduction kinetics. The results suggest
that a variety of organic surface-active substances might enhance or inhibit contaminant
degradation, depending on the degree to which they promote solubilization, sorption.
and/or reaction. Of particular interest is the effect of natural organic matter (NOM),
because of its ubiquitous presence in natural waters and amphiphilic properties; anthropogenic
surfactants, because of their use in groundwater remediation; and certain quinones,
which represent the redox-active functional groups associated with NOM. In this study,
no well-defined effects of these substances were found on the reduction of nitro benzene
by Fe0, but the reduction of carbon tetrachloride and trichloroethylene (TCE) was
inhibited by NOM. Results with carbon tetrachloride showed that the inhibitory effect
of humic acids was greater than fulvic acids, but that several quinonoid NOM model
compounds (juglone, lawsone. and anthraquinone disulfonate) increased the rate of
reduction by Fe0. Isotherms for adsorption of TCE and NOM onto Fe0 showed evidence
of competition for surface sites.