ИСТИНА

Liquid radioactive waste (LRW) represent serious environmental problem due to their multicomponent composition: presence of long-lived radionuclides with variable oxidation states as well as nitrate ion in high concentrations. One of the most problematic types of LRW are alkaline waste generated in the PUREX process of spent nuclear fuel recovery. Annually are generated about 6490 mm3 of alkaline LRW with pH>9, which contain uranium in concentration up to 3 g l¡1 and sodium carbonate in concentration range 80–150 g l¡1. The aim of the present work was to use microorganisms: bacteria Halomonas mono and cyanobacterium Arthrospira (Spirulina) platensis, isolated from extremely alkaline habitat for uranium removal from synthetic LRW. Elemental composition of microbial biomass was determined using neutron activation analysis at the pulsed fast reactor IBR-2 (FLNP JINR, Dubna). Biosorption experiments showed that bacteria Halomonas mono possess higher maximum biosorption capacity for uranium in comparison with cyanobacterium Arthrospira (Spirulina) platensis. The kinetics of uranium sorption onto studied microorganisms follows a pseudo-first order rate equation. The strong involvement of carboxyl, hydroxyl, carboxyl and amide groups in studied metals binding was ascertained by FTIR analysis and potentiometric titration. Bioreduction studies carried out with Halomonas mono cells showed highness of uranium reduction in alkaline conditions, resulting in the bioreduction of 64% of uranyl ions. Results of geochemical modeling showed formation of uraninite by Halomonas mono. It can be concluded that bacteria Halomonas mono can be efficiently applied for uranium removal from liquid alkaline radioactive waste by means of biosorption and bioreduction processes.