Impact of hydrothermal treatment of FEBEX and MX80 bentonites in water, HNO3 and Lu(NO3)3 media: Implications for radioactive waste control

•Bentonites exhibit good hydrothermal stability in water and acid media.•Lu2Si2O7 is formed during hydrothermal treatment of both bentonites in Lu3 + solution.•The formation of actinide analogous compound is more pronounced in MX80 than FEBEX.

Engineered barriers of deep geological repositories (DGR) are commonly constructed with bentonite. FEBEX and MX80 bentonites have been selected by different countries as reference materials for the sealing of repositories; however, their chemical reactivity with high-level long-lived radioactive wastes (HLRW) under subcritical conditions had not been explored before. The hydrothermal stability in neutral and acid media and chemical reactivity in contact with an actinide analogous compound were both studied. The long-range and short-range structural changes were analyzed by X-ray diffraction, nuclear magnetic resonance and scanning electron microscopy. Both bentonites have exhibited a good stability in neutral and acid media and have generated a new phase immobilizing the actinide analogous compound. The extent of the chemical reaction is higher in MX80 bentonite than in FEBEX bentonite.

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