We report on new and much more precise cation-exchange data of element 104, rutherfordium (Rf), in the fluoride ion concentration [F−] range of 5.29×10−5−1.04×10−3 M. The result based on one-atom-at-a-time chemistry clearly demonstrates that the distribution coefficients (Kd) decrease with increasing [F−], suggesting successive fluoride complexation of Rf. The complexation of Rf is briefly discussed in terms of fully relativistic density functional calculation theory.

We have investigated the cation-exchange behavior of element 104, rutherfordium (Rf), together with its lighter group-4 homologs Zr and Hf, and the tetravalent pseudo-homolog Th in HF/HNO3 mixed solution. The results, obtained on a one-atom-at-a-time scale, demonstrate that distribution coefficients (Kd) of Rf in HF/0.10 M HNO3 decrease with increasing concentration of the fluoride ion [F−]. This resembles the behavior of the homologs, indicating the consecutive formation of fluorido complexes of Rf. We also measured the Kd values of Rf and the homologs as a function of the hydrogen ion concentration [H+] in the range of [F−] = 5.29 × 10−7–3.17 × 10−6 M. The log Kd values decrease linearly with an increase of log[H+] with slopes between −2.1 and −2.5. This indicates that these elements are likely to form the same chemical compounds: mixture of [MF]3+ and [MF2]2+ (M = Rf, Zr, Hf, and Th) in the studied solution. It is also ascertained that the fluorido complex formation of Rf is significantly weaker than that of Zr and Hf, but it is stronger than that of Th.

Separation of 241AmIII from 152,154EuIII was carried out using an improved system of flow-counterbalanced capillary electrophoresis in a thiocyanate medium. In this system, EuIII was electrophoresed in the opposite direction to AmIII due to a combination of (1) the difference in the moving velocities of EuIII and AmIII, and (2) a constant flow in the capillary caused by a difference in the water levels of the inlet and outlet of the sample solution.

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