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/0.10M 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 logKd 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.
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