Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 52 (2019)

Anion and cation exchange of Pa in HF/HCl mixture solution for Db
chemistry
T. Yokokita∗1 and H. Haba∗1
Clarifying the chemical properties of superheavy elements with atomic number Z ≥ 104 is an intriguing andimportant subject. These elements are produced at accelerators using heavy-ion-induced nuclear reactions. The
production rates of these elements are low, and their halflives are short (T1/2 ≤ 1 min). Thus, chemical studies onthese elements are conducted on a single-atom basis.1)
F− ion is a very strong complexing agent for thegroup-5 elements (Nb and Ta). The ﬂuoride complex
species of the heaviest group-5 element, dubnium (Db),
is very interesting (Db forms [DbOFx ]n− or [DbFx ]n− )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 the ﬂuoride complex species of Db, we plan to perform an ionexchange study of Db. In this study, we performed anionand cation-exchange experiments of Pa (pseudo homologue of Db) in HF/HCl mixture solution to determine thesuitable experimental condition of Db and obtain comparable data for Db.
233
Pa was obtained as an α-decay daughter of 237 Np
in the following procedure. First, 237 Np in 9 M HCl containing 233 Pa was fed onto the TK400 resin’s (TRISKEM)
column. 237 Np was then eluted with 9 M HCl and 233 Pa
was adsorbed on the resin. The adsorbed 233 Pa species
was eluted with 1 M HCl. The eluent containing the Pa
tracers was evaporated and dissolved in 9 M HCl. Then,Pa nuclide was puriﬁed by anion-exchange column chromatography using a procedure found in Ref. 3).
In the anion-exchange experiments, the anion-exchange
resin (MCI GEL CA08Y) was added in 0.25 mL ofHF/HCl mixture solution containing 233 Pa in a PP tube
and the mixture was shaken using a mixer. Next, theresin was removed by centrifugation. Subsequently, theﬁltrate was pipetted into another tube, weighed, and subjected to γ-ray spectrometry using a Ge detector. The
concentration of HF and HCl was determined by titration with standardized NaOH solution before the experiments. In all anion-exchange experiments, control exper-Fig. 1. Kd values of Pa in anion exchange as a function of Cl−concentration.
∗1

RIKEN Nishina Center

Fig. 2. Kd values of Pa in cation exchange as a function ofH+ concentration.

iments without the resin were performed. We also performed cation-exchange experiments of Pa using a cationexchange resin (MCI GEL CK08Y). The experimental
procedures were the same as the anion-exchange experiments. The Kd values were determined from the following
equation:(1)
Kd = Ar Vs /As wr = (Ac − As )Vs /As wr

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 Pa as a function of Cl− concentrationin the anion-exchange experiment are shown in Fig. 1. Inanion exchange, the Kd values of Pa linearly decrease withincreasing concentration of Cl− in [F− ] = 10−6 − 10−2 M.
These results indicate that Pa forms anionic complexes
in the studied conditions. The slope values between log
Kd and log[Cl− ] are −1.4, −1.9, −1.6, −1.9, and −1.2
in [F− ] = 10−6 , 10−5 , 10−4 , 10−3 , and 10−2 M, respectively. These results indicated that the net charge of theadsorbed Pa species are −2 and −1.
The Kd values of Pa as a function of H+ concentrationin the cation-exchange experiment are shown in Fig. 2.
The Kd values of Pa were > 103 mL g−1 and Pa was adsorbed on the resin in [F− ] = 10− 7 − 10− 5 M and [H+ ]= 0.01 M. These results indicate that Pa forms cationicspecies in these F− concentrations. The linear relation
between log Kd and log [H+ ] is not obtained. It is suggested that some cationic Pa species coexist and/or Pa
forms chloride complexes.
Recently, we produced 95 Nb and 179 Ta (homologues ofDb) in the nat Zr(d, xn)95 Nb and nat Hf(d, xn)179 Ta reactions, respectively. We plan to study anion- and cationexchange behavior of Nb and Ta in HF/HCl using thesetracers for Db chemistry.
References1) 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).

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