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Sorption et transport réactif d'ions dans des monolithes de silice fonctionnalisés aux hexacyanoferrates pour le traitement d'effluents radioactifs

Abstract : The nuclear industry produces high amounts of contaminated water from various sources that require specific treatments depending on their chemical composition. Cesium-137 and strontium-90 are among the most abundant radionuclides in those effluents, which have to be removed as efficiently as possible in order to generate the lowest amount of waste. The column process is one of the most suitable processes to achieve this solid-phase extraction. Its principle is based on the sorption capacity of the radionuclide by copper hexacyanoferrates (HCF), highly cesium-selective mineral ion-exchangers. Investigations on HCF pointed out the structural effects of the cesium insertion within the crystal, which were linked to the high affinity of HCF for this ion. The functionalization of HCF on silica monolith with hierarchical pore structure was carried out in order to benefit the remarkable properties of these supports used as a column. Sorption kinetics evaluated down to trace concentrations have shown a fast capture of the cesium, which proves the interest of this material for a column process purpose. In addition, the performances of functionalized silica monolith have been highlighted in comparison with those made of particulate fixed beds. Finally, those materials were implemented for a simultaneous decontamination of cesium and strontium by a double extraction mechanism of ion exchange and coprecipitation of barium sulfate, allowed by the high permeability of the monolith. A simplified model of reactive transport was built with the HYTEC code, based on the actual morphology of the monolith. To do so, a dispersive flow in the macroporous intraskeletal channels and a diffusive flow inside the walls of the structure and the HCF aggregates were assumed.
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Submitted on : Monday, December 2, 2019 - 9:44:07 AM
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Clément Cabaud. Sorption et transport réactif d'ions dans des monolithes de silice fonctionnalisés aux hexacyanoferrates pour le traitement d'effluents radioactifs. Radiochimie. PSL Research University, 2019. Français. ⟨NNT : 2019PSLEM034⟩. ⟨tel-02388702⟩

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