Biosorption of long-lived radionuclides

摘要

The aim of our work was to study the possibility to reduce the volume of radioactive wastes, using the sorption of radioactive elements by biomass or transfer in less soluble state. We dealt with technetium-99 (half-life is 2.12* 10~5 y, specific activity - 1.7 mCi/mmol). The fungi Aspergillus niger, Scopulariopsis brevicaulis, yeasts, several species of Pseudomonas, thionic and sulfate-reducing bacteria were used in the experiments. The radioactivity of solution (Tc - 24 mg/l) was decreased on 58, 65 and 40 percent after contact with A. niger, & brevicaulis and yeast Pichia wicker, respectively. Anaerobic consortium of chromate-reducing bacteria removed techhetium-99 almost completely. The concentration factor was 4,1 * 10~3. In experiments with sulfate-reducing bacteria the radioactivity was decreased on 25-48 percent. Sulfides of technetium Tc_2S_7 and TcS_2 were formed. Vanadate-reducing bacteria decreased the radioactivity on 25 percent (concentration of Tc - 40 mg/l). The sorption by living cells was 4-5 times higher than by dead biomass. Thionic bacteria -Thiobacillus ferrooxidans and Thiobacillus thiooxidans can oxidize ferrous iron and sulfur in anaerobic conditions, using pertechnetate as electron acceptor. The decrease of radioactivity was 50-70 percent. By paper chromatography we shown that heptavalent technetium reduced to 4 and 5 valent states by cultures Pseudomonas vanadiumreductans in neutral conditions and thionic bacteria in acid media. Dead biomass of A. niger - a waste of citric acid plant was used in experiments for removing U, Am, Ce, Cs, Eu, Pa, Sb at joint presence. All elements were removed in different degree, which depends on their chemical properties and concentration.