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PM07 Pollutant Chemistry Transport, Cycling and Fate
(PM090) Reduction of Cr(VI) by Elemental Iron: Batch Study and Implications to Groundwater and Sediment Remediation.
Zhang, C1, Aman, M1, Hughes, J2, 1 University of Houston-Clear Lake, Houston, Texas, USA2 Georgia Institute of Technology, Atlanta, Georgia, USA
ABSTRACT- Chromium (Cr) is a metal used in many industrial and manufacturing processes that ultimately finds its way into groundwater and sediments of lakes, streams, and other waters. In nature chromium has two stable ionic states, non-toxic Cr(III) and the carcinogenic Cr (VI). Chromium (IV) is a U.S. EPA priority pollutant, and remediation of Cr(VI) contaminated groundwater and sediments is necessary. Laboratory studies were conducted to evaluate the feasibility of using zero-valent iron (ZVI) to reduce Cr(VI) under batch conditions with and without a sediment collected from Anacostia River, Washington, DC. Results indicate that Cr(VI) reduction rate increased as pHs and initial Cr(VI) concentrations decreased. The complete reduction took weeks or only hours at ambient pH 7.0 and environmentally relevant concentrations (1 mg/L). In the presence of sediment, reduction rate was enhanced as compared to the controls containing only iron or sediment. Studies with various sizes of ZVI further indicated that fine-grained cast iron powder is suitable for rapid reduction in groundwater remediation scenario while slow-releasing granular iron may be a better candidate for use in sediment remediation. Zero-order kinetics fit the reduction data under intensive mixing conditions, and first-order kinetics can be used to describe the reduction under static condition that rate-limiting factors such as available iron surface area may become important. The redox chemistry of Cr(VI)-Fe (0) and interactions with other chemical species (S2- and HCO3-) were also analyzed with MINTEQ speciation model.
Key words: zero-valent iron, Chromium, remediation, oxidation-reduction
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