Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 53

Anion exchange of Nb and Ta in HF/HCl mixture solution for DbchemistryT. Yokokita∗1 and H. Haba∗1105

Kd / mL g–1

10[F––] =10–3
M–5[F ] =10 M

4––4[F ] =10M

103
102
101
100

0.01

0.1
[Cl–] / M

RIKEN Nishina Center[F–] =10–3 M[F–] =10–5 M

105[F–] =10–4 M

104
103
102

0.01

0.1
[Cl–] / M

1Fig. 2. Kd values of Ta in anion exchange as a function ofCl− concentration.

following equation:
Kd = Ar Vs /As wr = (Ac − As )Vs /As wr ,(1)where Ar and As are the radioactivities on the resin andin the solution, respectively; Vs is the volume (mL) ofthe solution; and wr is the mass (g) of the dry resin. Ac
denotes the radioactivity of the control solution.
The Kd values of Nb and Ta as a function of Cl− concentration in the anion-exchange experiment are shownin Figs. 1 and 2, respectively. The values of Nb andTa linearly decrease with increasing Cl− concentration,except for Nb in [F− ] = 10−5 M. These results suggestthat Nb and Ta form anionic complexes in [F− ] ≥ 10−4and ≥10−5 M, respectively. The slope values betweenlog Kd and log [Cl− ] of Nb are −1.1 ± 0.1 and −1.3 ± 0.1
in [F− ] = 10−4 and 10−3 M, respectively. These results
indicate that the net charge of the adsorbed Nb species
is −1. For Ta, the slope values between log Kd and log[Cl− ] are −0.8 ± 0.1, −0.4 ± 0.1, and −0.8 ± 0.4 in [F− ]= 10−5 , 10−4 , and 10−3 M, respectively. These results
indicate that the net charge of the adsorbed Ta species
is −1 at [F− ] = 10−5 and 10−3 M. However, at [F− ] =10−4 M, the net charge of the adsorbed Ta species cannot
be determined.
We also obtained the Kd values of Nb and Ta as afunction of F− concentration in [HCl] = 0.1 M. We also
obtained those of Pa in our previous study.4) The sequence of the Kd values is Ta > Nb > Pa, and it is consistent with that in the HF/HNO3 mixture system.2,3)
This point suggests that the eﬀect of the chloride ion issmall for the complexation agent. On the other hand,another study is needed to check the eﬀect of chlorideion.
References

1Fig. 1. Kd values of Nb in anion exchange as a function ofCl− concentration.
∗1106

Kd / mL g–1

Clarifying the chemical properties of superheavy elements with atomic number (Z) ≥ 104 is an intriguing
and important subject. These elements are produced ataccelerators using heavy-ion-induced nuclear reactions.
The production rates of these elements are low, and theirhalf-lives are short (T1/2 ≤ 1 min). Thus, chemical studies on these elements are conducted on a single-atombasis.1)
The ﬂuoride ion is a very strong complexing agent forgroup-5 elements (Nb and Ta). The ﬂuoride complex
species of the heaviest group-5 element, dubnium (Db),
is very interesting (Db forms oxyﬂuoride or ﬂuoride complexes) because Nb and Ta form diﬀerent ﬂuoride complexes (Nb: [NbOF5 ]2− ; Ta: [TaF7 ]2− ) in 0.1–10 M HF([F− ] = 8.9 × 10−3 − 1.9 × 10−2 M).2) To determine theﬂuoride complex species of Db, we plan to perform anion-exchange study of Db. In this study, we performed
an anion-exchange experiment on Nb and Ta in HF/HClmixture solutions to determine the suitable experimental
conditions and obtain comparable data for Db.
We produced 95 Nb and 179 Ta in the nat Zr(d, xn)
and nat Hf(d, xn)179 Ta reactions (nat = natural isotopicabundance), respectively, by using the RIKEN AVF
cyclotron. These radiotracers were puriﬁed by theanion-exchange method using the procedure reported inRef. 3).
In the anion-exchange experiments, the anionexchange resin (MCI GEL CA08Y) was added to 0.25 mLof an HF/HCl mixture solution containing both 95 Nband 179 Ta in a PP tube, and the mixture was shaken using a mixer. Next, the resin was removed by centrifugation. Subsequently, the ﬁltrate was pipetted into anothertube, weighed, and subjected to γ-ray spectrometry using a Ge detector. The concentration of HF and HCl
was determined by titration with a standardized NaOH
solution before the experiments. In all anion-exchange
experiments, control experiments without the resin wereperformed. The Kd values were determined from the1) A. Türler, V. Pershina, Chem. Rev. 113, 1273 (2013).
2) Y. Kasamatsu et al., J. Radioanal. Nucl. Chem. 279, 371(2009).
3) Y. Kasamatsu et al., J. Nucl. Radiochem. Sci. 8, 69 (2007).
4) T. Yokokita, H. Haba, RIKEN Accel. Prog. Rep. 52, 186(2019).

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