Bentonote clays are widely used as engineering barrier materials for radioactive waste disposal into geological formations due to their low permeability, considerable sorption capacity in relation to radionuclides, good swelling ability, heat resistance, thermal conductivity. Nowdays several bentonites deposits in Russia and
CIS countries are currently being developed that are Zyryanskoe (Russia), 10th Khutor (Russia, Khakassia republic), Dashkovskoe (Russia), Taganskoe (CIS, Kazakhstan).
Possible transformations of bentonite barrier properties, which can happen when isolating liquid radioactive waste, were modeled by the treatment with concentrated nitric acid at 90 ° C during 5 hours.
Sorption of microquantities of 90-Sr, 137-Cs, 233-U, 241-Am was held from aqueous dispersions (liquid to solid ratio 1:100) and рН magnitude at 7.2-8. Results of sorption experiments are shown in Table 1.
Table 1. The results of radionuclides sorption on bentonite samples from distilled water
Bentonite sample Condition of samples Radionuclides adsorption (S,%) Specific surface area, m2 / g
90 Sr 137Cs 233U 241Am
Taganskoe natural 95 83 95 99 110,2
acid modified 99 98 98 99 280,1
Dashkovskoe natural 94 95 81 97 63,9
acid modified 99 98 99 99 135,4
10th Khutor natural 89 89 74 99 13,33
acid modified 94 89 95 99 95
Zyryanskoe natural 89 89 85 99 44,8
acid modified 99 96 96 96 192,98
Adsorption values of thermo-chemically modified bentonite samples appeared to exceed the values of adsorption for natural samples. Therefore the adsorption degree for 137Cs on natural Taganskoe bentonite is 83%, whereas on modified one it is 98%.
The increase in radionuclides sorption on modified bentonite clays samples is likely due to the transformation of surface properties. Acid treatment of bentonites resulted it washing the octahedral cations out as well as dissolvation of presumable organic films on the surface of the montmorillonite particles. That leads to an increase in the specific surface area and the appearance of relatively large pores. (Zakusin et al., 2015, Krupskaya et al., 2017).
Speciation of radionuclides were investigated by sequential extraction method.
This work was financed by the Russian Science Foundation (Project #16-17-10270).
Krupskaya, V., Zakusin, S., Tyupina, E., Dorzhieva, O., Zhukhlistov, A., Belousov, P., Timofeeva, M., 2017. Experimental Study of Montmorillonite Structure and Transformation of Its Properties under Treatment with Inorganic Acid Solutions. Minerals 7, 49. doi:10.3390/min7040049.
Zakusin S.V., Krupskaya V.V., Dorzhieva O.V., Zhuhlistov A.P., Tyupina E.A. Modification of theadsorption properties of montmorillonite by the thermochemical treatment. Сорбционные и хроматографические процессы. 2015. Т. 15. Вып. 6. С. 874-883.