Most raw montmorillonites (MMT) used for radioactive waste disposal (HLW) contain Ca in the interlayer space. When HLW and MMT come into contact, various ions, such as Sr2+ and Ba2+, enter the mineral. Therefore, the article presents the results of modeling, based on molecular dynamics, for four different models for the replacement of part of Ca2+ with Sr2+ and Ba2+ ions in Ca-MMT.

The general trend of MMT swelling does not change significantly after the introduction of Sr2+ and Ba2+ ions. The diffusion coefficient of water molecules increases with an increase in the number of H2O layers between mineral layers or the presence of a certain amount of large radius ions in the series Ca-MMT, Ca-Ba-MMT, Ca-Sr-MMT, Ca-Sr-Ba-MMT. It shown that in the state of single-layer clay hydration, all the studied cations form outer-sphere complexes. During two-layer clay hydration, Ca2+ tends to form outer-sphere complexes, while Sr2+ and Ba2+ ions predominantly form inner-sphere complexes. With a further increase in the number of water molecules, the interaction of Ca2+ with the basal surface of the MMT mineral layer increases.