RIKEN Accel. Prog. Rep. 48 (2015)

Ⅲ-3. Radiochemistry & Nuclear Chemistry

Liquid-liquid extraction of Nb and Ta with Aliquat 336
from 0.27 M HF solution
D. Sato,*1,*2 M. Murakami,*1,*2 K. Ooe,*1 H. Haba,＊2 H. Kikunaga,*3 S. Goto,*1 and H. Kudo*4
The elements with atomic numbers ≥ 104 are called
transactinide elements. Their chemical properties aregreatly interesting because it is expected that chemical
behavior of these elements would deviate from that oflighter homologs by strong relativistic effects on valence
electrons1). Therefore, it is very important to study thechemical behavior of transactinide elements comparing withthat of lighter homologs.
Among the transactinide elements, we are interested in thechemical properties of 105th element Db, especially, forcomplex formation with a fluoride ion which is a strong
complexing reagent for group 5 elements. Anionic fluoride
complex formation of Db has been investigated throughanion exchange study from HF solution2). The result of thisexperiment showed that the Kd value of Db in 13.9 M HF
was smaller than that of Nb and Ta, which are lighterhomologs of Db. However, the chemical form of Db was
not yet determined in this condition. Therefore, forinvestigation of fluoride complex formation of Db in detail,we have been studying the liquid-liquid extraction behaviorof Nb and Ta from HF solutions with quaternary ammonium
salt, Aliquat 336. So far, a clear difference of the extraction
behavior between Nb and Ta in 10-2-27 M HF was observed.
While distribution ratios (D) of Nb were decreased withincreasing HF concentration, those of Ta were a maximum
at around 0.3 M HF3). Since linear relations with slope ≈ 1
for both elements were observed from log D vs. log[Aliquat 336] plots, it was suggested that univalent anionic
fluoride complex of NbOF4- and TaF6- were extracted by
Aliquat 336 in 2.7 M and 10 M HF. However, in previous
study, we have not obtained information of chemical
species in 0.27 M which those of Ta are most extracted.
Therefore, in the present work, variation of D values of95gNb and 179Ta vs. concentration of Aliquat 336 in 0.27 M
HF was studied.
Long-lived radiotracers, 95gNb (T1/2 = 34.97 d) and 179Ta(T1/2 = 665 d), were produced during deuteron irradiation ofZr and Hf metallic foil targets with natural isotopic
abundances, respectively, using the RIKEN K70 AVF
Cyclotron. These radiotracers in the targets were chemicallyisolated by ion-exchange separation. The tracers weredissolved in 600 μL of 0.27 M HF and then mixed with thesame volume of 10-8-10-1 M Aliquat 336/1,2-dichloroethane
solutions in a polypropylene tube. After shaking of thesolutions for 5 min, followed by centrifugation, the twophases were separately pipetted into sample tubes. TheGraduate School of Science and Technology, Niigata University
RIKEN Nishina Center*3
Research Center for Electron Photon Science, Tohoku University*4
Department of Chemistry, Faculty of Science, Niigata University*1*2

radioactivities of the two samples were measured with a Ge
detector. D values of Nb and Ta were obtained from theratio of the radioactivities of the two phases.
The dependences of the distribution ratios of 95gNb and179
Ta in 0.27 M HF on the concentrations of Aliquat 336 areshown in Fig. 1. The results show a linear relation with aslope of ≈1 for both Nb ([Aliquat 336] = 10-5-10-1 M) andTa ([Aliquat 336] = 10-8-10-7 M), which indicates that
univalent anionic fluoride complexes are extracted byAliquat 336. Therefore, it is suggested that NbOF4- andTaF6- were also extracted by Aliquat 336 in 0.27 M HF
along with 2.7M and 10 M HF.

Fig. 1: Variation of the distribution ratio D of 95gNb and179
Ta vs. concentration of Aliquat 336 in 0.27 M HF.
From the obtained results and reference [4-5], it isassumed that the chemical species of Nb and Ta change
from NbOF4- to NbOF52- and from TaF6- to TaF72-,
respectively, with increasing HF concentration in the rangeof 0.27-10 M, expressed as following equations:NbOF4- + F- ↔ NbOF52-(1)TaF6- + F- ↔ TaF72-(2)

In the near future, dependence of D values of 95gNb andTa on concentration of Aliquat 336 in HF solution lower
than 0.27 M will be investigated for further study offluoride complex formation of group 5 elements.

179

References

1) P. Pyykko: Chem. Rev. 88, 563 (1988)
2) K. Tsukada et al.:,Radiochim. Acta 97, 83 (2009).
3) D. Sato et al.: Accel. Prog. Rep. 47 271 (2014).
4) F. Monroy Guzman et al.: J. Radioanal. Nucl. Chem. 208, 461(1996).
5) A. Agulyansky: The Chemistry of Tantalum and Niobium
Fluoride Compounds, 125-134- 286 -完全版2014_本文.indd 286

15/10/16 18:04