Biogeochemical factors of Uranium and Technetium migration in subsurface water near to RW repository
A. Safonov1, R. Aldabaev1, N. Andryushchenko1, K. Boldyrev2, T. Babich3, K. German1, E. Zakharova1, A. Novikov4
1A.N. Frumkin Institute of Physical Chemistry and Electrochemistry of Russian Academy of Sciences
2. The Nuclear Safety Institute (IBRAE) Russian Academy of Sciences
3. Research Centre of Biotechnology RAS Russian Academy of Sciences
4. V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry
The report presents our data on the impact of microbiological factors on the behavior of uranium and technetium in the upper aquifers (10-15 m) near to the radioactive waste surface repository (Russia, Tomsk region). Pollution of groundwater continued for 50 years, and now, in addition to radionuclides, the concentration of nitrate ions reached 5000 mg/L. Nitrate ions and some dissolved oxygen lead to high values of redox potential, forming conditions for high mobility of uranium and technetium in higher oxidation states.
In the samples of ground water an active microbial community capable of using nitrate, uranyl, pertechnetate ions for cell respiration was found. Treatment of microflora with organic substrates in the laboratory modeling tests has led to the microbial processes intensification followed with consumption of nitrate ions to molecular nitrogen, reduction of pertechnetate and uranyl ions to less soluble species. The results of geochemical modeling have shown that the immobilization of technetium in the environmental occurs mainly in the form of a tetravalent oxide and in a mixture with a biogenic sulfide. Uranium was immobilized as uraninite. Biogenic sulfide ions can play the role of an antioxidant buffer when new portions of the oxidant enter the system.
The process of formation of polysaccharide microbial biofilms on the host sand horizons was studied. It was found that in some cases microbial biofilms supported on the surface of minerals and rocks can increase their sorption capacity for uranium and technetium.
The work was supported by the Russian Science Foundation, project No. 17-17-01212.