Thermal and saline effects on the swelling deformation of montmorillonite: a molecular dynamics study

WJ Dai and YG Chen and WM Ye and Q Wang and DB Wu, BULLETIN OF ENGINEERING GEOLOGY AND THE ENVIRONMENT, 83, 11 (2024).

DOI: 10.1007/s10064-023-03506-8

Compacted bentonite is often considered the optimum buffering material in deep geological repository for high-level radioactive waste (HLRW). The investigation of Mt (montmorillonite) swelling behaviors under non- isothermal saline conditions is essential for understanding the buffering property deterioration of compacted bentonite. To reveal the coupling relationship of swelling deformation and interlayer molecular behaviors of Mt, molecular models of Mt-salt system were constructed. The cation exchange and swelling process were studied by molecular dynamics (MD) simulation. We find that counterion replacement is closely related to the interlayer interactions and hydrated complex structure. The entry of K+ and Ca2+ into the Na-Mt interlayer brings about a significant increase in its stability and water retaining capacity, enhancing local agglomeration of interlayer water molecules. This results in inhibition of the swelling deformation of Mt. Besides, elevated temperature reduces the order of interlayer water molecules and increases the interlayer ionic correlation, leading to an increase in basal space. However, these variations of interlayer properties are antagonistic for Mt swelling, resulting in a weaker thermal effect compared to the salination effect. And the swelling behaviors of Mt is essential to evaluate the final swelling deformation of bentonite. These findings provide a clear insight into the mineral changes in bentonite swelling from a molecular view.

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