B. H. Shabalin1, K. K. Yaroshenko1, 2, N. B. Mitsiuk1
1 State Institution “The Institute of Environmental Geochemistry of National Academy of Sciences of Ukraine”, 34-a, Acad. Palladin Ave, Kyiv, 03142, Ukraine
2 Institute of Geological Sciences of the National Academy of Sciences of Ukraine, 55-b, Olesia Honchara st., Kyiv, 01054, Ukraine
DOI: doi.org/10.31717/2311-8253.25.2.6
Abstract
The article presents the results of the experimental studies of physico-chemical properties of bentonite clays to assess the possibility of their use as engineered barrier components in radioactive waste disposal facilities at the “Vector” Complex. The object of the study are bentonite clays from the Cherkasy deposit of bentonite and palygorskite clays. Among the main physico-chemical characteristics that determine the technical and functional properties of clay barrier materials are the granulometric, mineral and chemical composition; bulk density, colloidity, moisture capacity, specific surface area; stability when interacting with a technogenic system; filtration properties under compression load, and sorption properties. However, the main attention should be paid to the sorption and filtration properties. In the sorption experiments, a high degree of strontium and caesium removal from model groundwater solutions of the “Vector” Complex is detected. The degree of 137Cs sorption from weakly alkaline (pH = 7.4) and lowsalt model solutions (with a Ca2+ concentration up to 16 mg/dm3 ) is over 96−99 % for the natural bentonite. With an increase in the Ca2+ cation concentration from 160 to 900 mg/dm3 and pH from 7.4 to 11.8, the degree of 137Cs sorption decreases to 80−86 %. At the same time, under these conditions, the maximum distribution coefficient of 137Cs is 4.8×103 ml/g. The degree of 90Sr sorption from weakly alkaline (pH = 7.4) and low-salt model solutions is 85 %. The maximum distribution coefficient is 0.7×103 ml/g. With an increase of the bentonite-model solution interaction time, the redistribution of mobile (exchangeable) and immobile (non-exchangeable) forms of 137Cs and 90Sr radionuclides is observed. The proportion of the non-exchangeable form which does not participate in the migration processes increases. The value of the filtration coefficient of the bentonite-sand mixture (mass ratio 1:4, density 1.92 g/cm3 ) depends on the hydraulic gradient and is on average 2.2 · 10-10 m/s at the gradient over 10, while at the hydraulic gradients less than 10, the filtration coefficient decreases sharply and drops to zero at the gradient less than 1.
Keywords: bentonite, Cherkasy deposit, isolation properties, caesium, strontium.
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