title: Modification of hectorite by organofunctionalization for use in removing U(VI) from aqueous media: thermodynamic approach.
abstract: A Hectorite sample (H) has been chemically modified with N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide. The resulting materials (H(3TPT) and H(NPTM)) have been characterized through elemental analysis, X-ray diffractometry, carbon nuclear magnetic resonance in the solid state, textural analysis, and thermogravimetric analysis. The adsorption experiments were performed under batch process with pH, ionic strength, contact time, and uranyl concentration as variables. The attached basic centers adsorbed uranyl cation to give maxima adsorption capacity of 5.55+/-0.21, 14.86+/-0.05, and 18.99+/-0.05 x 10(-3) mmol g(-1) for H, H(3TPT), and H(NPTM), respectively. From calorimetric determinations the quantitative thermal effects for UO(2)(2+)/center interactions gave exothermic enthalpy (Delta(int)H=-6.90 to -7.88 kJ mol(-1)), negative Gibbs free energy (Delta(int)G=-22.34 to -24.56 kJ mol(-1)), and positive entropy (Delta(int)S=51.80-56.00 JK(-1)mol(-1)). These thermodynamic data confirmed the energetically favorable condition of such interaction solid/liquid for all systems.
authors.affiliation: Universidade Federal de Mato Grosso, UFMT, Centro de Recursos Minerais, Cuiabá, Mato Grosso 78060 900, Brazil. dlguerra@pq.cnpq.br
authors.forename: Denis L
authors.initials: DL
authors.lastname: Guerra
authors.forename: Claudio
authors.initials: C
authors.lastname: Airoldi
authors.forename: Rúbia R
authors.initials: RR
authors.lastname: Viana
mesh_terms: D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D017646:Organosilicon Compounds / Q000737:chemistry*; D009994:Osmolar Concentration; D017640:Silicates / Q000737:chemistry*; D013057:Spectrum Analysis; D013816:Thermodynamics; D013997:Time Factors; D014501:Uranium / Q000302:isolation & purification*; D014875:Water Pollutants, Radioactive / Q000302:isolation & purification*; D014961:X-Ray Diffraction
chemical_list: D017646:Organosilicon Compounds; D017640:Silicates; D014875:Water Pollutants, Radioactive; C013547:hectorite; D014501:Uranium