Institute of Ore Geology, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Moscow, Russia:

V. V. Krupskaya, Senior Researcher, Candidate of Geological-Mineralogical Sciences, krupskaya@ruсlay.com

Lomonosov Moscow State University, Moscow, Russia:

S. V. Zakusin, Post-Graduate Student
M. S. Chernov, Senior Researcher, Candidate of Geological–Mineralogical Sciences

Mendeleev University of Chemical Technology of Russia, Moscow, Russia:

E. A. Tyupina, Assistant Professor, Candidate of Engineering Sciences

Bentonite is an important constituent of engineering barrier systems in high-level radioactive waste disposal. Probable alteration of composition, structure and properties of montmorillonite, as a main component of bentonite clay, is the determining factor in the short- and long-term prediction of stability of engineering barrier systems. Radioactive waste usually contain fission products (REE, transition metals, alkali and alkaline earth metals, etc.), and transuranium elements (plutonium, neptunium, americium, curium). Among them, cesium, as the most reactive element with a relatively long half-life period, is the most promising for the study, because it maintains radiation hazard for hundreds of years and plays an important role in migration of radionuclides. Features of cesium adsorption on montmorillonite in engineering barriers are yet not fully understood. This paper presents the results of experimental studies into adsorption of cesium on montmorillonite. It contains newly obtained and experimentally confirmed facts on Cs–O bonding between cation and oxygen in tetrahedral sheet of 2:1 montmorillonite. As a result of such bonding, Cs participates in the tetrahedral layer charge compensation, which leads to a reduction of the whole layer charge and to its redistribution between octahedral and tetrahedral sheets. Such conversion of the layer charge leads to the formation of large microaggregates carrying out face-to-face and edge-to-face interaction, as opposed to natural montmorillonite, where individual particles and ultra-microaggregates maintain edge-to-face interaction. Although the study was conducted on bentonite suspensions, the mechanism of transformation in composition, structure and properties will be similar to the compacted bentonite barrier systems. It can be assumed that adsorption of Cs in interlayer space of montmorillonite in bentonite barrier will bring it out of the migration processes, but it will reduce the swelling ability and increase the density and permeability of the barrier. The experimental results can be used in predicting stability of bentonite barriers for disposal of high level radioactive waste for the entire period of potential radiation hazard.
The authors are grateful to B. B. Zvyagina, Candidate of Geological-Mineralogical Sciences, Geological Institute, RAS, M. V. Vigasina, Senior Researcher, Geological Faculty, Lomonosov Moscow State University, and to O. V. Dorzhieva, Postgraduate student, Institute of Ore Geology, Petrography, Mineralogy and Geochemistry, RAS, for the assistance in infrared spectroscopy testing and the data interpreting, as well as to T. G. Shimko, M. L. Kuleshova and Z.P. Malashenko, Laboratory for Geological Environment Protection, Geological Faculty, Lomonosov Moscow State University, for the help in experimentation on cesium adsorption. The research was carried out using equipment delivered in the framework of development program for the Lomonosov Moscow State University.
The study was implemented under governmental order on “Highly Local Analysis of Mineral Composition and Structure”.

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