The ion-exchange behavior of Zr and Hf in H2SO4 and H2SO4/HClO4 mixed solutions has been studied by a batch method using the carrier-free radiotracers 88Zr and 175Hf. It is found that the ion-exchange behavior of Zr and Hf is basically similar to each other, and that Zr and Hf are adsorbed on the cation-exchange resin as well as on an anion-exchange one in H2SO4. In 0.11−0.99 M H2SO4, the logarithmic values of distribution coefficients (Kd) of Zr and Hf on the cation- and anion-exchange resins linearly decrease with log[H+]eq and log[HSO4-]eq, respectively, indicating that M4+ and M(SO4)32- (M=Zr and Hf) are the predominant cationic and anionic species adsorbed on the resins, respectively. The Kd values of Zr and Hf on the cation-exchange resin in H2SO4/HClO4 at [H+]eq=1.0 M also decrease with an increase of [HSO4-]eq, reflecting successive formation of sulfate complexes. The slope analysis demonstrates that Zr and Hf are coordinated by one SO42- ion at 0.011 and 0.020 M [HSO4-]eq, respectively, and by two SO42- ions at 0.079 and 0.20 M [HSO4-]eq, respectively.
We developed a new apparatus for the study of electrochemical properties of the heaviest elements. The apparatus is based on a flow electrolytic cell combined with column chromatography. Glassy-carbon fibers modified with Nafion perfluorinated cation-exchange resin are used as a working electrode as well as a cation-exchanger. The elution behavior of 139Ce with the number of 1010 atoms in 0.1 M ammonium α-hydroxyisobutyric acid solution from the column electrode was investigated at the applied potentials of 0.2–1.0 V versus the Ag/AgCl reference electrode in 1.0 M LiCl. It was found that 139Ce3+ is successfully oxidized to 139Ce4+ even with tracer concentration at around the redox potential determined by cyclic voltammetry for the macro amounts of Ce with 1017 atoms (10−3 M). The present oxidation reaction and separation of Ce4+ was accomplished within a few minutes.
Chemical studies on element 104, rutherfordium (Rf), at JAERI (Japan Atomic Energy Research Institute) are reviewed. The transactinide nuclide 261Rf has been produced in the reaction 248Cm(18O, 5n) at the JAERI tandem accelerator with the production cross section of about 13 nb. On-line anion-exchange experiments on Rf together with the lighter homologues, group-4 elements Zr and Hf, in acidic solutions have been conducted with a rapid ion-exchange separation apparatus. From the systematic study of the anion-exchange behavior of Rf, it has been found that the properties of Rf in HCl and HNO3 solutions are quite similar to those of Zr and Hf, definitely confirming that Rf is a member of the group-4 elements. However, we have observed an unexpected chemical behavior of Rf in HF solutions; the fluoride complex formation of Rf is significantly different from those of the homologues. Prospects of extending chemical studies on transactinide elements in the near future at JAERI are briefly considered.
Formation of anionic fluoride-complexes of element 104, rutherfordium, produced in the 248Cm(18O,5n) 261Rf reaction was studied by anion-exchange on an atom-at-a-time scale. It was found that the hexafluoro complex of Rf, [RfF6]2−, was formed in the studied fluoride ion concentrations of 0.0005–0.013 M. Formation of [RfF6]2− was significantly different from that of the homologues Zr and Hf, [ZrF6]2− and [HfF6]2−; the evaluated formation constant of [RfF6]2− is at least one-order of magnitude smaller than those of [ZrF6]2− and [HfF6]2−.
The extraction behavior of rutherfordium (Rf) into tributylphosphate (TBP) from hydrochloric acid (HCl) has been studied together with those of the lighter group-4 elements Zr and Hf. The extractability of 261Rf, 169Hf, and 85Zr into TBP was investigated under identical conditions in 7.2–8.0 M HCl by on-line reversed-phase extraction chromatography. The percent extractions of Rf, Hf, and Zr into the TBP resin increase steeply with increasing HCl concentration, and the order of extraction is Zr > Hf ≈ Rf. By considering the order of chloride complexation among these elements, it is suggested that the stability of the TBP complex of Rf tetrachloride is lower than those of Zr and Hf.