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Uranium retention in a Callovo-Oxfordian clay rock formation: From laboratory-based models to in natura conditions

Abstract : For the performance assessment of radioactive waste disposal, it is critical to predict the mobility of radionuclides in the geological barrier that hosts it. A key challenge consists of assessing the transferability of current knowledge on the retention properties deduced from model systems to in natura situations. The case of the redox-sensitive element uranium in the Callovo-Oxfordian clay formation (COx) is presented herein. Extensive experimental work was carried out with respect to parameters affecting uranium speciation (pH, PCO2, [Ca] and redox potential) with illite, COx clay fraction and raw COx claystone. The “bottom-up” approach implemented, with illite and montmorillonite as reactive phases, quantitatively explains the adsorption results of U(VI) and U(IV) on COx. While retention is high for U(IV) (Rd∼104 L kg−1), it remains very low for U(VI) (Rd∼4 L kg−1) due to the formation of soluble ternary Ca(Mg)–U(VI)-carbonate complexes. The applicability of the sorption model was then assessed by comparing predictive analyses with data characterizing the behavior of naturally-occurring U (<3 mg kg−1). The COx clay phase is the largest reservoir of naturally-occurring U (∼65%) but only a small fraction appears to be adsorbed (∼1%). Under representative site conditions (especially with respect to reducing conditions), we have concluded that ternary U(VI) complexes control U speciation in solution while U(IV) surface species dominate U adsorption, with Rd values > 70 L kg−1. (Elsevier)
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https://hal.archives-ouvertes.fr/hal-03623475
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Submitted on : Wednesday, November 23, 2022 - 12:38:15 PM
Last modification on : Friday, November 25, 2022 - 3:38:13 AM

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Gilles F Montavon, Solange Ribet, Y. Hassan Loni, F. Maia, C. Bailly, et al.. Uranium retention in a Callovo-Oxfordian clay rock formation: From laboratory-based models to in natura conditions. Chemosphere, 2022, 299, pp.134307. ⟨10.1016/j.chemosphere.2022.134307⟩. ⟨hal-03623475⟩

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