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Effet de la temperature sur les mécanismes d'interaction entre l'ion uranyle et l'oxophosphate de zirconium

Abstract : Uranium sorption onto Zr2O(PO4)2 has been studied between 298 K and 363 K, in 0.1M NaClO4 medium. Potentiometric titrations were realized to determine temperature dependency of the acid-base properties (pHpcn, acidity constants). Classical batch experiments were performed at different temperatures. The sorption experiments revealed that the uranium sorption onto Zr2O(PO4)2 is favoured with the temperature. Structural characterization of the surface complexes was performed by both Time-Resolved Laser-Induced Fluorescence (TRLIF) and EXAFS spectroscopy. The TRLIF measurements vs temperature revealed two uranyl surface complexes. No influence of the temperature onto the nature surface complex was observed. The EXAFS analysis showed a splitting of the equatorial oxygen atoms in two shells, corresponding to uranyl bidentate, inner-sphere complexes. The obtained structural uranyl surface complex information was used to simulate (using a constant capacitance model) the sorption edges. The proposed complexes equilibrium model consists of the following surface complexes: (>ZrOH)2UO22+ and (>PO)2UO2. Besides the stability constants for the surface complexes, the thermodynamic parameters ΔH° and ΔS° were determined using the van't Hoff equation. The enthalpy values associated to the U(VI) retention onto Zr2O(PO4)2, determined by the temperature dependence of the stability constants, testify that the formation of the complex (>PO)2UO2 (55 kJ/mol) is endothermic, while no influence of the temperature was observed for the formation of the complex (>ZrOH)2UO22+. The adsorption reaction of the last complex is then driven by entropy. In addition, calorimetric measurements of uranium sorpt
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https://tel.archives-ouvertes.fr/tel-00145065
Contributor : Maria Guadalupe Almazan-Torres <>
Submitted on : Monday, May 7, 2007 - 4:26:22 PM
Last modification on : Wednesday, September 16, 2020 - 4:08:13 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 11:12:57 PM

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Maria Guadalupe Almazan-Torres. Effet de la temperature sur les mécanismes d'interaction entre l'ion uranyle et l'oxophosphate de zirconium. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00145065⟩

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