title: Adsorption mechanism of selenate and selenite on the binary oxide systems.
abstract: Removal of selenium oxyanions by the binary oxide systems, Al- or Fe-oxides mixed with X-ray noncrystalline SiO(2), was previously not well understood. This study evaluates the adsorption capacity and kinetics of selenium oxyanions by different metal hydroxides onto SiO(2), and uses X-ray absorption spectroscopy (XAS) to assess the interaction between selenium oxyanions and the sorbents at pH 5.0. The binary oxide systems of Al(III)- or Fe(III)-oxides mixed with SiO(2) were prepared, and were characterized for their surface area, point of zero charge (PZC), pH envelopes, X-ray diffraction analysis (XRD), and then macro-scale adsorption isotherm and kinetics of selenite and selenate, micro-scale adsorption XAS. The adsorption capacity of selenite and selenate on Al(III)/SiO(2) is greater than on Fe(III)/SiO(2). Adsorption isothermal and kinetic data of selenium can be well fitted to the Langmuir isotherm and pseudo-second-order kinetic models. Based on simple geometrical constraints, selenite on both the binary oxide systems forms bidentate inner-sphere surface complexes, and selenate on Fe(III)/SiO(2) forms stronger complexes than on Al(III)/SiO(2).
authors.affiliation: Department of Agricultural Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
authors.forename: Ya Ting
authors.initials: YT
authors.lastname: Chan
authors.forename: Wen Hui
authors.initials: WH
authors.lastname: Kuan
authors.forename: Tsan Yao
authors.initials: TY
authors.lastname: Chen
authors.forename: Ming Kuang
authors.initials: MK
authors.lastname: Wang
mesh_terms: D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010087:Oxides / Q000737:chemistry*; D064586:Selenic Acid; D018036:Selenium Compounds / Q000737:chemistry*; D018038:Sodium Selenite / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D014961:X-Ray Diffraction
chemical_list: D010087:Oxides; D018036:Selenium Compounds; D018038:Sodium Selenite; D064586:Selenic Acid