ИСТИНА

The role of microbial and biogenic-mediated colloids on actinide behavior in subsurface radioactive wastes repository environment (10-15 m) and in deep underground aquifers (380- 400 m) nearby the deep well injection radioactive waste repositories (Russia, Tomsk region) were studied. These sites have been operating for more then 50 years for disposal of radionuclide solutions containing nitrate ions. The current concentration of nitrate ions in aquifers is up to 5000 mg/l. Using 16S rRNA genes sequencing technique we have found an active microbial community capable of reducing major radioactive wastes macrocomponents (nitrates, sulfates, etc.) in ground water. Glucose stimulation tests led to microflora activation which caused Eh decreasing up to -300 mV, consumption of nitrate ions with producing molecular nitrogen, reduction of sulfates to sulfides and uranyl ions to U(IV) consequently. This study was dedicated to behavior of laboratory stimulated microbial communities in water ambient in presence of clay particles and iron containing phases. It has been shown that microbial activity led to colloidal particles coagulation with time. Coagulation of clay colloids occurred to be rapid process in simulated deep underground water, whereas in iron containing solution coagulation was slower due to formation of organic stabilized ferrous colloids. Formation of large pseudo-colloidal particles of complex structure followed by coagulation was found in real deep underground water. It was shown that in 21 days particles with size of more than 200 nanometers in size appear. In 104 days content of particles larger than 200 nm increased by 60-80%. In the meanwhile neptunium and uranium concentrations in solutions containing microbiota were reduced by 60–90% depending on metal concentration. In control solution (without microbiota) neptunium was generally found as a part of colloidal particles of 5-50 nanometers in size. Considering that actinides in +4 oxidatiuon state are very inclined to hydrolytic polymerization which products of microbial activity, they can form rather large particles due to association and adsorption. The proportion of Np(VI) and Np(V) in microbiota containing solutions associated with particles over 200 nm obtained by filtration was estimated as 15–18% and 11–25% respectively while in the control solution no particles larger than 200 nanometers have been revealed. The critical coagulation concentration (CCC) values for the considered colloids and zeta potentials have been defined. The thermodynamic model of Np and U containing colloidal particles formation and the kinetic model of coagulation and size distribution of colloidal particles has been developed. The modeling of the considered colloidal particles transport through a model column has been carried out.