Surface chemical reactivity in selected zero-valent iron samples used in groundwater remediation

Permeable iron barriers have become a popular choice as a passive, cost-eff ective in situ remediation technology for chlorinated solvents. However, lo ss of reactivity over time, due to a build up of corrosion products or othe r precipitates on the iron surface, is a great concern, Because first-order rate constants for trichloroethylene (TCE) degradation have differed by ir on pre-treatment and sonication history, X-ray photoelectron spectroscopy ( XPS) was used to explore the changes in near surface chemistry of several i ron samples. Both sonicated and unsonicated filings were analyzed in unwash ed and groundwater-soaked conditions. Unsonicated acid-washed iron, with th e highest first-order rate constant for TCE degradation, was characterized by greater surface oxygen content and was more ionic relative to the unwash ed samples. The unsonicated, unwashed sample, with the lowest rate constant , exhibited a mixture of nonstoichiometric iron oxide and oxyhydroxide spec ies. Sonication of groundwater-soaked iron removed weakly bonded iron hydro xide species and decreased the ionic character of the surface as was observ ed in the unwashed samples. Thus, this type of study might provide a better understanding of the chemical reactivity of selected iron samples and desi gn better material in remediation technology. (C) 2000 Elsevier Science B.V . All rights reserved.