ИСТИНА

Being a transition element technetium (Tc) is exclusively interesting for investigations as it has 8 states of oxidation (between -1 and +7) and other specificities. The main source of Tc accumulation is the nuclear power industry. Today the management of radioactive waste containing Tc still causes the range of problems coming from its long half-life and high mobility in the form of a pertechnetate ion. There are also many complications with the radioactive waste containing Tc disposal since it has a low ability to immobilize in matrices and barrier materials and has high risks of uncontrolled migration in the environment. Bentonite clay is one of the most promising natural barrier materials for a multi-barrier system in radioactive waste disposal sites due to its low water permeability, high plasticity, and high sorption capacity (for Cs, Sr actinides) properties. Nevertheless, if the clay contains little of dissolved humic substances, reduced iron, sulfide sulfur, which have reducing properties, immobilization of technetium does not occur. Therefore, one of the promising areas of research for many groups today is the creation of a barrier material based on clays and concretes capable of immobilizing technetium. For this purpose, reducing additives are traditionally used, for example, ZVI, fly ash and others, which promote the immobilization of technetium in the +4 form. This study investigates bentonite clay from the 10th Khutor deposit (Khakassia) as a promising barrier material for the "Yeniseisky" deep geological repository for radioactive waste in the Krasnoyarsk Region. The clay was modified with both organic (thiourea) and mineral (reduced iron, ferrihydrite, etc.) additives. The experiments demonstrated that the addition of 5 wt.% iron powder resulted in a technetium sorption degree of 99%. Quantitative removal of technetium was achieved within 8 hours, with a residual content of no less than 36% of the technetium retained in a strongly fixed form. Furthermore, the incorporation of thiourea into the clay also led to the quantitative immobilization of technetium from the solution. Thiourea acts by effectively modifying technetium speciation, reducing it from the highly mobile pertechnetate ion [Tc(VII)] to immobile forms of Tc. Structural analysis of the resultant technetium-thiourea compound confirmed a reductive immobilization mechanism. This work was supported bу the Ministry of Science and Higher Education of the Russian Federation