title: Selenate removal by zero-valent iron in oxic condition: the role of Fe(II) and selenate removal mechanism.
abstract: In this study, batch experiments were conducted to investigate the effect of the concentration of ferrous [Fe(II)] ions on selenate [Se(VI)] removal using zero-valent iron (ZVI). The mechanism of removal was investigated using spectroscopic and image analyses of the ZVI-Fe(II)-Se(VI) system. The test to remove 50 mg/L of Se(VI) by 1 g/L of ZVI resulted in about 60% removal of Se(VI) in the case with absence of Fe(II), but other tests with the addition of 50 and 100 mg/L of the Fe(II) had increased the removal efficiencies about 93 and 100% of the Se(VI), respectively. In other batch tests with the absence of ZVI, there were little changes on the Se(VI) removal by the varied concentration of the Fe(II). From these results, we found that Fe(II) ion plays an accelerator for the reduction of Se(VI) by ZVI with the stoichiometric balance of 1.4 (=nFe(2+)/nSe(6+)). Under anoxic conditions, the batch test revealed about 10% removal of the Se(VI), indicating that the presence of dissolved oxygen increased the kinetics of Se(VI) removal due to the Fe(II)-containing oxides on the ZVI, as analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectra also showed that the reductive process of Se(VI) to Se(0)/Se(-II) occurred in the presence of the both ZVI and Fe(II). The final product of iron corrosion was lepidocrocite (γ-FeOOH), which acts as an electron transfer barrier from Fe(0) core to Se(VI). Therefore, the addition of Fe(II) enhanced the reactivity of ZVI through the formation of iron oxides (magnetite) favoring electron transfer during the removal of Se(VI), which was through the exhaustion of the Fe(0) core reacted with Se(VI).
authors.affiliation: Decontamination and Decommissioning Research Division, Korea Atomic Energy Research Institute, Daejeon, 305-353, Republic of Korea. ihyoon@kaeri.re.kr.
authors.forename: In-Ho
authors.identifier: http://orcid.org/0000-0001-8740-0573
authors.initials: IH
authors.lastname: Yoon
authors.affiliation: Korea Mine Reclamation Corporation (MIRECO), 30 Chungjin-dong Street, Jongno-gu, Seoul, 1100-727, Republic of Korea.
authors.forename: Sunbaek
authors.initials: S
authors.lastname: Bang
authors.affiliation: Department of Environmental Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea.
authors.forename: Kyoung-Woong
authors.initials: KW
authors.lastname: Kim
authors.affiliation: Pohang Accelerator Laboratory (PAL), Pohang, 790-784, Republic of Korea.
authors.forename: Min Gyu
authors.initials: MG
authors.lastname: Kim
authors.affiliation: Decontamination and Decommissioning Research Division, Korea Atomic Energy Research Institute, Daejeon, 305-353, Republic of Korea.
authors.forename: Sang Yoon
authors.initials: SY
authors.lastname: Park
authors.affiliation: Decontamination and Decommissioning Research Division, Korea Atomic Energy Research Institute, Daejeon, 305-353, Republic of Korea.
authors.forename: Wang-Kyu
authors.initials: WK
authors.lastname: Choi
mesh_terms: D000327:Adsorption; D052203:Ferrosoferric Oxide / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D064586:Selenic Acid / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D005296:Ferrous Compounds; D007501:Iron; D064586:Selenic Acid; D052203:Ferrosoferric Oxide
keywords: Ferrous ion; Iron corrosion; Oxic condition; Selenate; ZVI