Palladized iron (Pd/Fe) has been successfully used for the rapid dechlorination of organic environmental contaminants in aqueous solutions. We have investigated the nature of the Pd/Fe surface by X-ray photoelectron spectroscopy. Our results indicate that the reactive Pd/Fe surface is formed by the stepwise reduction of Pd(IV) in solution to Pd(II), which replaces protons on the hydroxylated iron oxide surface and forms Pd(II)-O-Fe bonds. These bonds are unstable and collapse spontaneously to yield the reactive palladized iron in which the palladium is in the elemental state. Prolonged exposure of this Pd/Fe surface to a saturated solution of aqueous TCE results in the growth of the hydroxylated iron oxide film that deactivates the Pd/Fe surface. The thick hydroxylated iron oxide film can be removed, and the original activity of the Pd/Fe surface can be restored by washing the surface with a dilute acid solution.
Trichloroethene (TCE) was reduced with zero‐valence iron and palladized iron in zero‐head‐space extractors. Progress of the reaction in these batch studies was monitored with purge‐and‐trap gas chromatography and a flame ionization detector. When a 5 ppm initial concentration of TCF. reacts with zero‐valence iron, approximately 140 ppb of vinyl chloride persists for as long as 73 days. The concentration of vinyl chloride (approximately If) ppb) remaining with palladized iron is approximately an order of magnitude less than when zero‐valence iron is the reductant. These data suggest that volatile byproducts may be under‐represented in oilier published data regarding reduction with zero‐valence metals. These results also demonstrate that the reduction of TCE with palladized iron (0.05 percent palladium) is more than an order of magnitude faster than with zero‐valence iron. Wilh a 5:1 solution‐to‐solid ratio the TCE half‐life with zero‐valence iron is 7.41 hours. but is only 0.59 hours with the palladized iron.
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