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Cs-137 immobilization in C-S-H gel nanopores


Cementation is a widespread technique to immobilize nuclear wastes due to the low leachability of cementitious materials. The capacity of calcium silicate hydrate (C-S-H), the main component of cement, to retain radionuclide Cs has been empirically studied at the macroscale, yet the specific molecular scale mechanisms that govern the retention have not been determined. In this work, we employed molecular dynamics simulations to investigate the adsorption and diffusivity of Cs into a C-S-H gel nanopore. From the simulations, it was possible to distinguish three types of Cs adsorption configurations on the C-S-H surface: an inner-sphere site where Cs is strongly bound, an outer-sphere site where Cs is loosely bound, and Cs free in the nanopore. For each configuration, we determined the adsorption energy, and the diffusion coefficients, up to two orders of magnitude lower than in bulk water due to the effect of nanoconfinement in the worst case scenario. It has also proved that Cs cannot displace to the intrinsic Ca from the C-S-H surface, and we calculated the binding strength and the residence time of the cations in the surface adsorption sites. Finally, we quantified the average number of adsorption sites per nm2 of C-S-H surface. All these results are the first insight of Cs retention in cement at the molecular scale and will be useful to build macroscopic diffusion models and devise cement formulations to improve radionuclide Cs retention from spent nuclear fuel.

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Publication details

The article was received on 29 Jan 2018, accepted on 14 Mar 2018 and first published on 14 Mar 2018

Article type: Paper
DOI: 10.1039/C8CP00654G
Citation: Phys. Chem. Chem. Phys., 2018, Accepted Manuscript
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    Cs-137 immobilization in C-S-H gel nanopores

    E. DUQUE REDONDO, Y. Kazuo, I. López-Arbeloa and H. Manzano, Phys. Chem. Chem. Phys., 2018, Accepted Manuscript , DOI: 10.1039/C8CP00654G

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