title: Sn(II) oxy-hydroxides as potential adsorbents for Cr(VI)-uptake from drinking water: An X-ray absorption study.
abstract: The feasibility of implementing a Sn(II) oxy-hydroxide (Sn6O4(OH)4) for the reduction and adsorption of Cr(VI) in drinking water treatment was investigated using XAFS spectroscopies at the Cr-K-edge. The analysis of the Cr-K-edge XANES and EXAFS spectra verified the effective use of Sn6O4(OH)4 for successful Cr(VI) removal. Adsorption isotherms, as well as dynamic Rapid Small Scale Test (RSSCT) in NSF water matrix showed that Sn6O4(OH)4 can decrease Cr(VI) concentration below the upcoming regulation limit of 10μg/L for drinking water. Moreover, an uptake capacity of 7.2μg/mg at breakthrough concentration of 10μg/L was estimated from the RSSCT, while the residual Cr(VI) concentration ranged at sub-ppb level for a significant period of the experiment. Furthermore, no evidence for the formation of Cr(OH)3 precipitates was found. On the contrary, Cr(III)-oxyanions were chemisorbed onto SnO2, which was formed after Sn(II)-oxidation during Cr(VI)-reduction. Nevertheless, changes in the type of Cr(III)-inner sphere complexes were observed after increasing surface coverage: Cr(III)-oxyanions preferentially sorb in a geometry which combines both bidentate binuclear ((2)C) and monodentate ((1)V) geometries, at the expense of the present bidentate mononuclear ((2)E) contributions. On the other hand, the pH during sorption does not affect the adsorption mechanism of Cr(III)-species. The implementation of Sn6O4(OH)4 in water treatment technology combines the advantage of rapidly reducing a large amount of Cr(VI) due to donation of two electrons by Sn(II) and also the strong chemisorption of Cr(III) in a combination of the (2)C and (1)V configurations, which enhances the safe disposal of spent adsorbents.
authors.affiliation: Aristotle University of Thessaloniki, School of Chemical Engineering, Analytical Chemistry Laboratory, 54124 Thessaloniki, Greece.
authors.forename: Fani
authors.initials: F
authors.lastname: Pinakidou
authors.affiliation: Aristotle University of Thessaloniki, School of Chemical Engineering, Analytical Chemistry Laboratory, 54124 Thessaloniki, Greece.
authors.forename: Efthimia
authors.initials: E
authors.lastname: Kaprara
authors.affiliation: Aristotle University of Thessaloniki, School of Physics, Department of Solid State Physics, 54124 Thessaloniki, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Katsikini
authors.affiliation: Aristotle University of Thessaloniki, School of Physics, Department of Solid State Physics, 54124 Thessaloniki, Greece.
authors.forename: Eleni C
authors.initials: EC
authors.lastname: Paloura
authors.affiliation: Aristotle University of Thessaloniki, School of Physics, Department of Solid State Physics, 54124 Thessaloniki, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Simeonidis
authors.affiliation: Aristotle University of Thessaloniki, School of Chemical Engineering, Analytical Chemistry Laboratory, 54124 Thessaloniki, Greece. Electronic address: manasis@eng.auth.gr.
authors.forename: Manassis
authors.initials: M
authors.lastname: Mitrakas
mesh_terms: D000327:Adsorption; D002857:Chromium / Q000032:analysis / Q000737:chemistry*; D060766:Drinking Water / Q000737:chemistry*; D052918:Environmental Restoration and Remediation / Q000379:methods; D017971:Tin Compounds / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*; D018508:Water Purification / Q000379:methods*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D060766:Drinking Water; D017971:Tin Compounds; D014874:Water Pollutants, Chemical; D002857:Chromium; C074702:chromium hexavalent ion; C045358:stannic oxide
keywords: Cr(VI) removal; EXAFS; Sn(II) oxy-hydroxides; XANES; water treatment