Investigation of the surface properties and microstructure of TiO_2 sorbents prepared in supercritical CO_2 for the treatment of Sr~(2+) contaminated effluents

摘要

Nuclear facilities generate contaminated effluents containing radionuclides (such as Cs, Sr, Co…) that need to be removedfor human health and environment protection reasons. Inorganic sorbents are attractive candidate materials becauseof their high thermochemical and radiation stability. Furthermore, their microstructural and surface properties can beadjusted to increase the radionuclide extraction efficiency. In this study, nanostructured sorbents consisting of aggregatedTiO_2nanocrystals with different surface properties and microstructures were prepared in supercritical CO_2byvarying the synthesis temperature. The Sr~(2+)sorption process was characterized by measuring the surface propertiesand extraction capacity of the samples as a function of pH. In basic effluents, the Sr sorption capacity of these materialsis directly linked to their specific surface area and sorption site density through a classic physisorption mechanism. Sr~(2+)diffusion into the mesopores leads to rapid initial sorption, which is followed by a slower process driven by a proposedmultistep mechanism. This mechanism involves the initial adsorption of partially hydrated Sr~(2+)ions up to complete TiO_2surface coverage, which implies slower Sr ion diffusion due to steric hindrance in small mesopores thus limiting accessto additional secondary sites with lower adsorption energies.