Radiochemical method for assessment of plutonium after radionuclide interaction with microorganisms

Abstract

In this study, referring to the co-precipitation method (Lovett and Nelson 1981), separation of oxidized and reduced plutonium fractions was achieved. Based on differences in property to form (Pu - IV) and not to form (Pu - III) anionic complexes in high molar (8 mol/L) HNO3 solution, the anion exchange method for separation and determination of Pu (V, VI), Pu (III) and Pu (IV) was developed. The developed radiochemical method was examined using real samples. Fungi Absidia spinosa and Paecilomyces lilacinus as well as Gram-positive bacteria Bacillus mycoides and Rhodococcus luteus and one morphotype of Gram-negative bacterium isolated from the samples in the radioactive waste repository territory were tested for their ability to participate in Pu(IV) redox reactions. To determine Pu in its different oxidation states the method of Pu co-precipitation with neodymium fluoride and the modified anion exchange method were applied. Alpha spectrometric counting following radiochemical analysis showed that out of tested microorganisms the highest ability to change Pu oxidation state should be attributed to bacteria Bacillus mycoides and Gram–negative bacterium. Pu (IV) after its interaction with above-mentioned bacteria for 24 hours in brine at pH 2.7-2.9 under aerobic conditions was reduced by up to 15 % to valence (III) plutonium.