Article

Adsorption mechanism of selenate and selenite on the binary oxide systems

Department of Agricultural Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
Water Research (Impact Factor: 5.53). 08/2009; 43(17):4412-20. DOI: 10.1016/j.watres.2009.06.056
Source: PubMed

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).

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    • "Considerable number of studies has been conducted on selenite adsorption in different types of minerals and its influential factors (Kamei-Ishikawa et al. 2007; Peak 2006; Chan et al. 2009). Chan et al. (2009) characterized the behavior of selenite at the adsorbent surface using X-ray absorption spectroscopy (XAS) and X-ray diffraction. However, soil is not a simple combination of OM and minerals but is rather a multiphase, inhomogeneous complex system. "
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    ABSTRACT: Purpose Selenium (Se) adsorption influences its mobility, transformation, and bioavailability in soil. Se interactions with soils and soil constituents have focused primarily on selenite retention. The dominant factors of selenite adsorption behavior and the impacts of exogenous Se concentration were investigated for the prediction of the rate of retention and release of selenium species in soils and the guidance of Se supplementation implementation. Materials and methods Eighteen typical agricultural soils with varying physicochemical characteristics and mineralogical composition were collected throughout China for the study of their adsorption and desorption behavior toward selenite and the effect of their physicochemical properties. Results and discussion Results showed that Se adsorbances among 18 soils varied considerably. Among numerous soil properties and components, soil pH exerted a significant negative effect on selenite adsorption in soil, whereas amorphous iron and amorphous aluminum had positive effect (P P K d) had no significant correlation with soil properties, other than with pH (P K d values of different soils were highly variable. Conclusions The observed adsorption behavior of selenite in soil is complicated: small amounts of exogenous Se were mainly adsorbed by a monolayer physical process, but multilayer adsorption occurred when the concentration increased. The soils that strongly adsorb selenite often showed low desorption rates, as well, which largely limited the migration, transformation, and bioavailability of selenite in soils. Therefore, residue problem must be considered when Se fertilizers are applied to these soils.
    Full-text · Article · May 2015 · Journal of Soils and Sediments
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    • "Adsorption kinetics A pseudo-second-order kinetic model was applied to fit the collected kinetic data. The kinetic rate equation is expressed as [9] [10] "

    Full-text · Article · Jan 2015
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    • "In natural environment, single oxide minerals are scarcer than binary oxide, thus it is presumed that the interaction of particles in binary oxide systems possibly influences the adsorption mechanism of adsorbents produced from such systems [14] [15]. Consequently, the oxyanions abstraction potentials of binary metal oxide (BMO) systems are being tested [16] [17] [18] [19] [20]. Thus far, the BMO of interest to researchers, for oxyanion abstraction, comprised of mainly transition metals; hence there is paucity of information on performance evaluation of mixed metal oxides of transition origin and alkali earth metals in this respect. "
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    ABSTRACT: Owing to the recent discovery about the potentials of pyrophosphate (PP) as a contributor to eutrophication, the ability of a binary metal oxide (BMO) as an adsorbent for PP removal from aqua system was investigated. The choice of a BMO was based on the synergy of the constituent metal oxides in sequestrating ionic species. The binary metal oxide (BMO) of Ca and Fe, synthesized using a Gastropod shell, as precursor, exhibited high removal efficiency (>99%) for pyrophosphate (PP), irrespective of initial PP concentration studied (25–300 mg/L). The pseudo second order kinetic model had the best (r2 − 1.00) fitting to the time-concentration profile data. The determination of the saturation index (SI) value of calcium pyrophosphate and application of the principle of constant solubility product affirmed the role of precipitation as a paramount factor in the PP removal process by BMO, in addition to the complex formation between any of the ionic species (i.e. Ca and Fe) in the system. The XRD analysis of the derived sludge revealed the formation of amorphous calcium pyrophosphate. Process variables optimization revealed that initial solution pH, organic load, and ionic strength had no negative impact on the PP removal efficiency. The results of the equilibrium isotherm analysis showed that the Freundlich isotherm equation gave the best description of the sorption process (r2 = 0.9109) and the Langmuir monolayer sorption capacity (qm, mg/g) value of 120.48 was obtained.
    Full-text · Article · Jun 2014 · Journal of Water Process Engineering
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