Solvent extraction of uranium, neptunium, plutonium, americium, curium and californium ions by bis(1-phenyl-3-methyl-4-acylpyrazol-5-one) derivatives

Comprehensive study has been performed on the extraction of actinide ions of various oxidation states, Ann+ (An=U, Np, Pu, Am, Cm and Cf), with bis(1-phenyl-3-methyl-4acylpyrazol-5-one) derivatives, H2BPn (n; number of polymethylene chain=3, 4, 5, 6, 7, 8, 10 and 22). All H2BPn derivatives showed higher extraction efficiencies for Ann+ than 1phenyl-3-methyl-4-benzoylpyrazol-5-one (HPMBP) did, which is attributable to the strong multidentate interaction with Ann+ or high hydrophobicity of H2BPn in comparison with HPMBP. The highest efficiency for all Ann+ examined was obtained with H2BP8 or H2BP7. The extracted species were confirmed as An(BPn)(HBPn) for Am3+, Cm3+ and Cf3+, and An (BPn)2 for U4+, Np4+ and Pu4+. The extracted species of UO22+ depended on the length of the polymethylene chain. The species UO2(HBPn)2 was extracted with H2BP3 or H2BP4 and UO2(BPn) with H2BPn of n=5. NpO2+ was hardly extracted from the solution of pH less than 9. On the basis of the correlation between the distribution ratio and pH the procedure for the successive separation of the actinides in nitric acid medium was developed. The recommended procedure using H2BP8 was applied to the mutual separation of UO22+, NpO2 +, Pu4+ and trivalent transplutonium ions.