ИСТИНА

The most modern concepts for the isolation of radioactive waste, especially high‐level waste, are based on the use of a multi‐barrier system in which bentonite is a one of the important components of engineering safety barriers. Currently, the Russian Federation is considering a concept for the construction of a deep disposal facility for radioactive waste in the Nizhne‐ Kansky massif (Krasnoyarsk region). The construction of the Underground Research Laboratory (Exploratory Rock Laboratory In Krasnoyarsk region ‐ ERLIK) has already begun and full‐scale experiments are planned to begin in 2021 In this regard, the identification of structural criteria and stability of montmorillonite in aggressive conditions will allow to make predictions of the evolution of the properties of engineering barriers for the near and far prospects with higher accuracy. This work presents the results of an experimental study of changes in the composition, structure and properties of bentonites from industrial deposits in Russia and the near abroad (Kazakhstan, Azerbaijan), which are considered promising for the isolation of radioactive waste. The experiments were carried out under acidic (in the presence of HNO3 solutions) and alkaline (KOH) conditions at room (~ 25 ° C) and high (90 ° C) temperatures during various time intervals (from 1 hour to 1 year). As a research methods were used: XRD, FTIR, DTG/TG, XRF, ICP‐MS, Sbet, pore size and volume, grain size, adsorption (including radionuclides). The conducted studies led to the conclusion that one of the most important structural criteria for the stability of montmorillonites under such conditions is the predominance of cis or trans‐vacant octahedra. All studied montmorillonites with a predominance of trans‐ vacant octahedra showed low resistance to thermochemical treatments compared to montmorillonites with a predominance of cis‐vacant octahedra. This criterion turned out to be more pronounced than the actual number of isomorphic substitutions of Al, Mg or Fe