Adsorption mechanisms of cesium at calcium-silicate-hydrate surfaces using molecular dynamics simulations

JOURNAL OF NUCLEAR MATERIALS

卷:515

Article

Bu, J.¹  Teresa, R. Gonzalez¹  Brown, K. G.¹  Sanchez, F.¹ 

[1] Vanderbilt Univ, Dept Civil & Environm Engn, PMB 351831,2301 Vanderbilt Pl, Nashville, TN 37235 USA

关键词: Tobermorite;    Jennite;    Radionuclides;    Cement phases;    Immobilization;   

DOI  :  10.1016/j.jnucmat.2018.12.007

来源: Elsevier

【 摘 要 】

Understanding the mechanisms of interactions and immobilization of radionuclides in cement systems at the molecular level is key to developing safe and novel solutions for the long-term storage of nuclear wastes. The molecular level adsorption mechanisms of cesium (Cs+) ions onto tobermorite 9 angstrom, tobermorite 14 angstrom, and jennite - three crystalline structural analogues for calcium-silicate-hydrates, the main components in cement-based materials, were investigated using molecular dynamics (MD) simulations. Convergence monitoring of the simulations, using the root mean square displacement with average correlation analysis, indicated that MD trajectories of 10-15 ns were needed given the size of the selected computational cell to properly capture the dynamic process of adsorption. Cs+ ions adsorbed as inner-sphere complexes at the tobermorite surfaces, while they showed lower affinity for jennite. The charge and structure of the surface layer strongly influenced the adsorption mechanisms of Cs+ ions. Strong association with the hexagonal cavities of the silica sites were seen at the tetrahedral SiO4 surface of the tobermorite structures. Cs+ ion adsorption was attributed to co-ion adsorption at the octahedral CaO6 surface of tobermorite 9 angstrom, cation exchange at that of tobermorite 14 angstrom, and electrostatic interaction with the surface hydroxyl groups for jennite. Distribution coefficients of Cs+ ions onto cement pastes derived from molecular dynamics by taking the surface structure and dynamics of Cs+ ions directly into account showed a range of overlap with experimental results. (C) 2018 Elsevier B.V. All rights reserved.

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