Reduction of Se(VI) to Se(-II) by zerovalent iron nanoparticle suspensions
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The reaction of selenate (Se(VI)) with zerovalent iron nanoparticles (nano Fe0) was studied using both conventional batch equilibrium and X-ray spectroscopic techniques. Nano Fe0 has a high uptake capacity for removal of dissolved Se(VI) reaching concentrations as high as 0.10 Se:Fe molar ratio in the solid product mixture. Kinetic studies of the Se(VI) uptake reaction in batch experiments showed an initial reaction rate (0–30 min) of 0.0364 min−1 which was four times greater than conventional Fe0 powder. Analysis of the oxidation state of Se in the solid products by X-ray absorption near edge structure (XANES) spectroscopy showed evidence for the reduction of Se(VI) to insoluble selenide (Se(-II)) species. Structural analysis of the product by extended X-ray absorption fine structure (EXAFS) spectroscopy suggested that Se(-II) was associated with nano Fe0 oxidation products as a poorly ordered iron selenide (FeSe) compound. The fitted first shell Se–Fe interatomic distance of 2.402 (±0.004) Å matched closely with previous studies of the products of Se(IV)-treated Fe(II)-clays and zero-valent iron/iron carbide (Fe/Fe3C). The poorly ordered FeSe product was associated with Fe0 corrosion product phases such as crystalline magnetite (Fe3O4) and Fe(III) oxyhydroxide. The results of this investigation suggest that nano Fe0 is a strong reducing agent capable of efficient reduction of soluble Se oxyanions to insoluble Se(-II).
KeywordsFe nanoparticles Reduction Selenium(VI) Selenium(-II) SEM EXAFS Soils Radioactive waste
We thank Matt Newville (APS-GSECARS) for assistance with XAS data collection and Sam Webb (SSRL) for assistance with SIXpack software work. The XAS work was performed at GSECARS (Sector 13, APS), Argonne National Laboratory, which is supported by the NSF (EAR-0217473), the U.S. DOE (DE-FG02-94ER14466), and the State of Illinois. This work was supported by the Research Corporation Cottrell College Science Program (CC6462 and CC5444) and the NSF-MRI program (0421285).
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