Bentonite stability,speciation and migration behaviour of some critical radionuclides

The contribution is focused on chemical, geochemical and mineralogical research of bentonite stability with the aim to determine the effect of saturation medium composition and loading by heat on bentonite stability. The main part of the research is directed to the experimental results of bentonite and bentonite leachate samples obtained for the bentonite interaction under laboratory experiments. Computer-modeling methods were used to calculate equilibrium thermodynamic principles, the distributions of predominant aqueous species, and potential solubility controls for the environmentally important oxidation states of each investigated radioactive contaminants. The Eh–pH diagrams of individual chemical species of the tested radionuclides were calculated by the geochemical software tool Geochemist’s Workbench that included the actual chemical compositions of the solid–liquid systems under the given experimental conditions. It was confirmed that smectites are transformed to more stable silicate phases, such as illite/smectite mixed layers, illite. The data obtained from the model calculations conform with experimental results. The effect of the variable aqueous phase composition on bentonite stability using Ca–Mg and Na–Ca bentonites for the experiments was studied. The synthetic granitic waters with the higher concentration of the K⁺ and Mg²⁺ cations were applied for the study of bentonite stability.