Journal of Nuclear and Radiochemical Sciences, Vol. 13, No.1, pp. 9-12, 2013

ArticlesAdsorption Behavior of 95Nb and 179Ta as Homologues of Element 105, Db, on Cation
Exchanger in HF/HNO3 Solution
Yoshitaka Kasamatsu,a,b,* Atsushi Toyoshima,a Hayato Toume,a Kazuaki Tsukada,aMasato Asai,a Hiromitsu Haba,c and Yuichiro NagameaaAdvanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japanc
Nishina Center for Accelerator-Based Science, RIKEN, Wako, Saitama 351-0198, Japanb

Received: January 23, 2013; In Final Form: June 7, 2013
Adsorption behavior of the group-5 elements, 95Nb and 179Ta, on cation-exchange resin was studied in mixed solution of HF and HNO3 (HF/HNO3) as a model experiment of their heavier homologue, element 105 (dubnium, Db).
Chemical reactions of these elements in the cation exchange rapidly reached the equilibrium. It was found that
distribution coefficients of Nb and Ta decrease with increasing the fluoride ion concentration in the studied rangeof 10 −7–10 −5 M. Clear difference between Nb and Ta was observed in the variations of the distribution coefficients
against the fluoride ion concentration. This would originate from their different chemical species of fluoride complexes. We propose the cation-exchange experiment of Db based on the present experimental results to understandits fluoride complex formation.

1. Introduction
Relativistic effects on orbital electrons become increasingly
strong in transactinide elements with the atomic number Z ≥104 because of high positive charges of nuclei of these heavy
atoms. As a consequence of the mass increase of the innershell electrons, these electrons are stabilized. In contrast, theouter shell electrons are destabilized due to enhanced shieldingof the nuclear charge by the inner shell electrons. Thus,
chemical properties of the transactinide elements cannot be
deduced from those of lighter homologues.1,2 Chemical studies
on these elements are very attractive for many chemists.
Furthermore, studies of the transactinides produced in heavyion-induced nuclear reactions are fairly challenging. Becauseof low production rates and short half-lives of the transactinide
nuclides, chemical experiments of these elements must be
conducted on a single atom scale.3 Partition experiments suchas column chromatography are required to be performed within
the lifetime of an objective nuclide. In addition, chemical
reactions should be fast to rapidly reach the equilibrium. Thesesituations make it very difficult to study chemical properties of
the transactinide elements. Prior to carrying out chemical
experiments with the transactinide elements, therefore, we needto search for suitable chemical reaction systems and to
determine appropriate conditions of the experiments for theseelements. For these purposes, generally, chemical experiments
using homologues of respective transactinide elements are
performed. Through these experiments, we can also obtaincomparative data to discuss the chemical properties of thetransactinide elements.
So far, solution chemistry was conducted mainly for thelighter transactinide elements, rutherfordium, 10 4 Rf, anddubnium, 105Db. For Db, only a few experiments to investigate
its chemical behavior such as a distribution equilibrium in twophase partition have been carried out4– 6 after some primarychemical experiments such as a mutual separation.7–11 In ourprevious studies,12–15 anion- and cation-exchange behavior of
Rf has been investigated in detail using the automated ion*Corresponding author. E-mail: kasa@chem.sci.osaka-u.ac.jp
Fax: +81-6-6850-5418

exchange separation apparatus coupled with the detection
system for alpha spectroscopy (AIDA).16 Interesting results
have been obtained especially in the f luoride complex
formation; the properties of Rf are largely different from thoseof the homologues. Following these successful works, using
the apparatus and method, adsorption behavior of Db on anion
exchanger has been studied together with its homologues Nb
and Ta and the pseudo-homologue Pa in HF6 and in the mixed
solution of HF and HNO3 (HF/HNO3).4 In 13.9 M HF solution,
the adsorption of Db on the resin is weaker than that of Nb andTa, and is stronger than or equal to that of Pa within counting
statistics.6 This provided the adsorption sequence of Ta ≈ Nb >Db ≥ Pa which qualitatively follows inverse sequence of theirionic radii. In 0.31 M HF/0.1 M HNO3, it was found that theadsorption behavior of Db is similar to that of Nb and Pa, while
the adsorption of these elements is clearly weaker than that of
Ta.4 The adsorption sequence of Ta > Nb ≥ Db ≥ Pa is different
from the order of the ionic radii, suggesting that chemical
species in this solution should be different among these group5 elements. In more dilute fluoride ion concentration, [F−], thebehavior of the cationic fluoride complexes is expected to beinvestigated by cation-exchange method. The cation-exchange
behavior of Db in addition to the anion-exchange one4,6 leads tofurther understanding of its fluoride complexation. The cationexchange behavior of the cationic fluoride complexes of Nb
and Ta is not well-known, although the cation-exchange
technique has been applied to the chemical separations of theseelements.17,18 It is difficult to investigate the behavior of theseelements in aqueous solutions without ligand anions due totheir instabilities and polymerizations in macro amounts.17
In this paper, we report adsorption behavior of Nb and Ta on
cation-exchange resin in HF/HNO3 solution using carrier-freeradiotracers 95Nb and 179Ta to obtain fundamental information
about cationic fluoride species of Nb and Ta and this is a modelexperiment of Db. After examining cation-exchange kineticsof 95 Nb and 179 Ta, distribution coefficients (Kd [mL g−1]) in
equilibrium are determined for these elements as a function of[F − ]. The fluoride complex formation of Nb and Ta are
discussed based on the present results together with the results
obtained in the anion-exchange experiment in the HF/HNO3
solution.4© 2013 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 06/19/2013

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Kasamatsu

J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013

104

2. Experimental

Kd =

ArVs
,
As m r(1)

where Ar and As are the radioactivities in the resin and solution,
respectively, Vs is the volume of the solution (mL), and mr is themass of the dry resin (g). In the present experiment, the radioactivity in the resin, A r , was evaluated by subtracting theradioactivity in the supernatant solution, As, from that in thestandard solution.
According to the results of the above kinetics experiments,
the Kd values of 95Nb and 179Ta in equilibrium were determined
as a function of [F−] in 10 −5 –10 −3 M HF/0.1 M HNO3 with themixing time of 1440 min.
3. Results and Discussion
In Figures 1 (a), 1(b), and 1(c), the Kd values of 95 Nb and
Ta in the cation exchange are shown as a function of themixing time in 10 −5 , 10 − 4 , and 10 −3 M HF/ 0.1 M HNO 3 ,respectively. The fluoride ion concentrations in these solutions
were calculated to be 1.1 × 10 −7, 1.1 × 10 −6, and 1.1 × 10 −5 M,
respectively, using the dissociation constants of HF and HF2−.20
As shown in Figures 1(a) to 1(c), the Kd values of Nb and Ta
are almost constant in the studied time range of 10–2880 min,except for those of Ta at [F−] = 1.1 × 10 −7 M. This means thatthe cation-exchange and fluoride-complexation reactions
reached the equilibrium states more rapidly than the studied
time range. For Ta, in the lowest concentration solution at [F−]= 1.1 × 10 −7 M, these reactions might be relatively slow.
Figure 2 shows variations of the Kd values of 95Nb and 179Ta
179

Nb
Ta

-

(a) [F ] = 1.1

-7

10 M

102

Kd / mL g

-1

10

3

101

100
10-1
0
104

Nb
Ta

-

(b) [F ] = 1.1

-6

10 M

102

Kd / mL g

-1

103

3000

2000
1000
Time / min

101
100
10-1
0
10

103
-1

1000
2000
Time / min

4

Nb
Ta

-

(c) [F ] = 1.1

3000
-5

10 M

102

Kd / mL g

The nuclides 95 Nb (T1/2 = 34.97 d) and 179 Ta (T1/2 = 665 d)were produced in the proton bombardments of nat Zr and nat Hf
metallic foil targets, respectively, at the RIKEN K70 AVF
cyclotron. The incident energy of the proton beam was 14 MeV
with the beam current of approximately 5 µA. The 95Nb and179
Ta radiotracer solutions were prepared by the same method
as described in our previous paper19 and were stocked in 0.001
and 0.01 M HF solutions in perfluoro alkoxy (PFA) tubes.
The cation-exchange resin used was a strongly acidic cationexchanger MCI GEL CK08Y with a particle size of 25 µm suppl ie d f rom M it subish i C hem ica l Cor p or at ion. T hecommercially available resin in the Na+ form was washed with
distilled water and then stirred in 2 M HNO3 and 2 M NaOH
solutions alternately three times. After stirred in 2 M HNO3,
the resin was washed with distilled water until it is neutralized,
and then dried in a vacuum oven at 70 °C for 24 h. After
grinding the resin, it was kept in a desiccator.
Kinetics of the cation-exchange reaction for 95Nb and 179Ta
was investigated in 10 −5, 10 −4 , and 10 −3 M HF/0.1 M HNO3
solutions by measuring the time dependence of the Kd values in
the cation exchange. The dried resin with a weight of 20–100
mg and 3 mL of HF/HNO3 solution containing the 95 Nb and179
Ta radiotracer solution were mixed in a polypropylene (PP)
tube. The mixture was shaken at 22 ± 1 °C and then separated
by centrifugation. Mixing time which includes the time consumed for the shaking and centrifugation was varied between
10 and 2880 min. After centrifugation, 1 mL of the supernatantsolution was precisely pipetted into a small polyethylene tube
and it was subjected to γ-ray spectrometry using a Ge detector.
A standard 1 mL solution of 95Nb and 179Ta was prepared in thesame way without the resin and was subjected to γ-ray
spectrometry. Non-adsorption of these radiotracers onto walls
of PFA and PP tubes was also verified in 10 −5, 10 −4, and 10 −3 M
HF/0.1 M HNO3 by the same method as that in Reference 19.
The distribution coefficient in an ion exchange is obtained
from eq 1:

101
100
10-1
0

1000
2000
Time / min

3000

Figure 1. Distribution coefficients of 95Nb and 179Ta as a function of
mixing time in (a) 10 −5, (b) 10 −4, and (c) 10 −3 M HF/0.1 M HNO3
solutions. The values of 95Nb and 179Ta are depicted by open triangles
and open circles, respectively.

in the cation exchange as a function of [F−] in HF/0.1 M HNO3.
For comparison, the Kd values of 95Nb and 179 Ta in the anion
exchange previously obtained in HF/0.1 M HNO3 4 are alsoplotted. As [F−] increases, the Kd values of Nb and Ta in the
cation exchange decrease in the studied [F − ] range between
10 −7 and 10 −5 M, representing that the abundance of the cationiccomplexes of Nb and Ta in the solution decreases withincreasing [F − ] owing to the consecutive formation of theneutral and anionic fluoride complexes. This result gives aconsistent picture with their anion-exchange behavior that theKd values increase with increasing [F−]. The Kd values in boththe cation and anion exchange are low around [F−] of 10 −5 and10 −6 M for Nb and Ta, respectively, suggesting that the neutral
complexes of these elements are dominant in each concentration
range.
The stable oxidation states of Nb and Ta in aqueous solution
are both +5 and their ionic radii in the same coordination

Adsorption Behavior of 95Nb and 179Ta as Homologues of Element 105

-1

11

102

on the cation-exchange resin was clearly different between Nb
and Ta in the studied [F−] range of 10 −7–10 −5 M. This suggeststhat the chemical species of the f luoride complexes aredifferent between these elements. The investigation on the
cation-exchange behavior of Db under the present experimental
conditions would lead to the further understanding of thefluoride complex formation of Db.

101

Acknowledgement

100

The authors express their gratitude to the crew of the RIKEN
K70 AVF cyclotron for their invaluable assistance in the production of 95Nb and 179Ta.

104

Kd / mL g

J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013

Nb (CIX)Ta (CIX)

103

10-1

10-7

10-6

Nb (AIX) 4
Ta (AIX) 4

10-5 10-4[ F- ] / M

Figure 2. Distribution coefficients of

95

10-3

10-2

179

Nb and Ta in the
cation exchange (CIX) in HF/0.1 M HNO3 solutions as a function of the fluoride ion concentration together with the data of95
Nb and 179Ta obtained in our previous anion-exchange (AIX)
experiment4. The plots of 95Nb and 179Ta obtained in this work
are depicted by open triangles and open circles, respectively,
and those of 95Nb and 179Ta in the anion exchange are shown as
closed triangles and closed circles, respectively.

number are almost the same. The charge densities of thecomplexes of Nb and Ta are, therefore, expected to be very
close with each other if these metal ions form the complexes
with the same configuration. Indeed, the group-4 elements Zr
and Hf, having the +4 stable oxidation state and very closeionic radii, form the same complexes and represent similar
adsorption behavior on resins.12–15 In contrast, the adsorption
behavior on the cation- and also anion-exchange resin is clearly
different between Nb and Ta as shown in Figure 2. In ourprevious report,4 different behavior between Nb and Ta in theanion-exchange distribution was attributed to the difference intheir chemical species; Nb forms oxo-fluoro complexes and Ta
forms fluoride complexes,21–24 which leads to higher Kd valuesof Ta than those of Nb. For the present results, therefore, it
could be also suggested that Nb and Ta exist as different
cationic species in the studied [F−] range between 10 −7 and 10 −5
M. Metal ions of Nb and Ta may form the complexes such as
fluoride or oxo-fluoro species with different positive charges.
Otherwise, Nb may form oxo-fluoro complexes having lower
charge densities than those of the fluoride complexes the sameas that in higher [F−] range,21–24 which leads to lower Kd valuesof Nb than Ta.
We are planning to perform the on-line cation-exchange
experiment of Db as well as Nb and Ta under the present
conditions. Formation of the cationic fluoride complexes of Db
will be investigated by comparing the data for Db with thepresent ones for Nb and Ta. The comprehensive discussion
with the results obtained in the anion- and cation-exchange
experiments will further deepen understanding of theproperties of the fluoride complexes of Db.
4. Conclusion
Cation-exchange behavior of 95Nb and 179Ta was studied in
HF/0.1 M HNO3 by batch method. It was found that reaction
kinetics of both the elements in the cation exchange is fast
under the present experimental conditions, whereas that of Ta
in the solution with the lowest [F − ] of 10 −7 M may not be
sufficiently fast. The Kd values of Nb and Ta decreased withincreasing [F−], indicating that the neutral and anionic fluoride
complexes are formed as [F−] increases. Adsorption behavior

References(1) M. Schädel, The Chemistry of Superheavy Elements ed. M.
Schädel (Kluwer Academic Publishers, Dordrecht, 2003).
(2) M. Schädel, Angew. Chem. Int. Ed. 45, 368 (2006).
(3) R. Guillaumont, J. P. Adloff, A. Peneloux, and P.
Delamoye, Radiochim. Acta 54, 1 (1991).
(4) Y. Kasamatsu, A. Toyoshima, M. Asai, K. Tsukada, Z. J.
Li, Y. Ishii, H. Toume, T. K. Sato, T. Kikuchi, I. Nishinaka,
Y. Nagame, H. Haba, H. Kikunaga, Y. Kudou, Y. Oura, K.
Akiyama, W. Sato, K. Ooe, H. Fujisawa, A. Shinohara, S.
Goto, T. Hasegawa, H. Kudo, T. Nanri, M. Araki, N.
Kinoshita, A. Yokoyama, F. L. Fan, Z. Qin, Ch. E.
Düllmann, M. Schädel, and J. V. Kratz, Chem. Lett. 38,
1084 (2009).
(5) W. Paulus, J. V. Kratz, E. Strub, S. Zauner, W. Brüchle, V.
Pershina, M. Schädel, B. Schausten, J. L. Adams, K. E.
Gregorich, D. C. Hoffman, M. R. Lane, C. Laue, D. M.
Lee, C. A. McGrath, D. K. Shaughnessy, D. A. Strellis, andE. R. Sylwester, Radiochim. Acta 84, 69 (1999).
(6) K. Tsukada, H. Haba, M. Asai, A. Toyoshima, K. Akiyama,
Y. Kasamatsu, I. Nishinaka, S. Ichikawa, K. Yasuda, Y.
Miyamoto, K. Hashimoto, Y. Nagame, S. Goto, H. Kudo,
W. Sato, A. Shinohara, Y. Oura, K. Sueki, H. Kikunaga, N.
Kinoshita, A. Yokoyama, M. Schädel, W. Brüchle, and J. V.
Kratz, Radiochim. Acta 97, 83 (2009).
(7) M. K. Gober, J. V. Kratz, H. P. Zimmermann, M. Schädel,W. Brüchle, E. Schimpf, K. E. Gregorich, A. Türler, N. J.
Hannink, K. R. Czerwinski, B. Kadkhodayan, D. M. Lee,
M. J. Nurmia, D. C. Hoffman, H. Gäggeler, D. Jost, J.
Kovacs, U. W. Scherer, and A. Weber, Radiochim. Acta 57,
77 (1992).
(8) K. E. Gregorich, R. A. Henderson, D. M. Lee, M. J.
Nurmia, R. M. Chasteler, H. L. Hall, D. A. Bennett, C. M.
Gannett, R. B. Chadwick, J. D. Leyba, D. C. Hoffman, and
G. Herrmann, Radiochim. Acta 43, 223 (1988).
(9) J. V. Kratz, H. P. Zimmermann, U. W. Scherer, M. Schädel,W. Brüchle, K. E. Gregorich, C. M. Gannett, H. L. Hall, R.
A. Henderson, D. M. Lee, J. D. Leyba, M. J. Nurmia, D. C.
Hoffman, H. Gäggeler, D. Jost, U. Baltensperger, Ya. NaiQi, A. Türler, and Ch. Lienert, Radiochim. Acta 48, 121(1989).
(10) M. Schädel, W. Brüchle, E. Schimpf, H. P. Zimmermann,
M. K. Gober, J. V. Kratz, N. Trautmann, H. Gäggeler, D.
Jost, J. Kovacs, U. W. Scherer, A. Weber, K. E. Gregorich,
A. Türler, K. R. Czerwinski, N. J. Hannink, B.
Kadkhodayan, D. M. Lee, M. J. Nurmia, and D. C.
Hoffman, Radiochim. Acta 57, 85 (1992).
(11) H. P. Zimmermann, M. K. Gober, J. V. Kratz, M. Schädel,W. Brüchle, E. Schimpf, K. E. Gregorich, A. Türler, K. R.
Czerwinski, N. J. Hannink, B. Kadkhodayan, D. M. Lee,
M. J. Nurmia, D. C. Hoffman, H. Gäggeler, D. Jost, J.
Kovacs, U. W. Scherer, and A. Weber, Radiochim. Acta 60,
11 (1993).
(12) H. Haba, K. Tsukada, M. Asai, A. Toyoshima, K. Akiyama,

12

J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013

I. Nishinaka, M. Hirata, T. Yaita, S. Ichikawa, Y. Nagame,K. Yasuda, Y. Miyamoto, T. Kaneko, S. Goto, S. Ono, T.
Hirai, H. Kudo, M. Shigekawa, A. Shinohara, Y. Oura, H.
Nakahara, K. Sueki, H. Kikunaga, N. Kinoshita, N.
Tsuruga, A. Yokoyama, M. Sakama, S. Enomoto, M.
Schädel, W. Brüchle, and J. V. Kratz, J. Am. Chem. Soc.
126, 5219 (2004).
(13) A. Toyoshima, H. Haba, K. Tsukada, M. Asai, K. Akiyama,
S. Goto, Y. Ishii, I. Nishinaka, T. K. Sato, Y. Nagame, W.
Sato, Y. Tani, H. Hasegawa, K. Matsuo, D. Saika, Y.
Kitamoto, A. Shinohara, M. Ito, J. Saito, H. Kudo, A.
Yokoyama, M. Sakama, K. Sueki, Y. Oura, H. Nakahara,
M. Schädel, W. Brüchle, and J. V. Kratz, Radiochim. Acta
96, 125 (2008).
(14) Y. Ishii, A. Toyoshima, K. Tsukada, M. Asai, H. Toume, I.
Nishinaka, Y. Nagame, S. Miyashita, T. Mori, H.
Suganuma, H. Haba, M. Sakamaki, S. Goto, H. Kudo, K.
Akiyama, Y. Oura, H. Nakahara, Y. Tashiro, A. Shinohara,
M. Schädel, W. Brüchle, V. Pershina, and J. V. Kratz,
Chem. Lett. 37, 288 (2008).
(15) Y. Ishii, A. Toyoshima, K. Tsukada, M. Asai, Z. Li, Y.
Nagame, S. Miyashita, T. Mori, H. Suganuma, H. Haba,
M. Sakamaki, S. Goto, H. Kudo, K. Akiyama, Y. Oura, A.
Shinohara, M. Schädel, V. Pershina, and J. V. Kratz, Bull.
Chem. Soc. Jpn. 84, 903 (2011).
(16) Y. Nagame, K. Tsukada, M. Asai, A. Toyoshima, K.

Kasamatsu
Akiyama, Y. Ishii, T. S. Kaneko, M. Hirata, I. Nishinaka, S.
Ichikawa, H. Haba, S. Enomoto, K. Matsuo, D. Saika, Y.
Kitamoto, H. Hasegawa, Y. Tani, W. Sato, A. Shinohara, M.
Ito, J. Saito, S. Goto, H. Kudo, H. Kikunaga, A. Yokoyama,
K. Sueki, Y. Oura, H. Nakahara, M. Sakama, M. Schädel,W. Brüchle, and J.V. Kratz, Radiochim. Acta 93, 519(2005).
(17) B. Remenec and S. Dulanská, J. Radioanal. Nucl. Chem.
295, 907 (2013).
(18) R. Caletka and V. Krivan, Talanta 30, 465 (1983).
(19) Y. Kasamatsu, A. Toyoshima, H. Toume, K. Tsukada, H.
Haba, Y. Nagame, J. Nucl. Radiochem. Sci. 8, 69 (2007).
(20) P. M. Plaisance and R. Guillaumont, Radiochim. Acta 12,
32 (1969).
(21) D. Schumann, S. Fischer, R. Dressler, St. Taut, H. Nitsche,
N. Trautmann, M. Schädel, W. Brüchle, B. Schausten, A. F.
Novgorodov, R. Misiak, B. Eichler, H. Gäggeler, D. Jost,
A. Türler, and H. Bruchertseifer, Radiochim. Acta 72, 137(1996).
(22) R. Caletka and V. Krivan, J. Radioanal. Nucl. Chem. 142,359 (1990).
(23) O. L. Keller and S. A. Chethan, Inorg. Chem. 5, 367(1966).
(24) D. Trubert, F. Monroy-Guzman, C. Le. Naour, L. Brillard,
M. Hussonnois, and O. Constantinescu, Anal. Chim. Acta
374, 149 (1998).