III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Solvent extraction of Zr and Hf from HCl by Aliquat 336 using aflow-type extraction apparatus toward online chemical studiesof element 104, rutherfordium†
Y. Kasamatsu,∗1 N. Kondo,∗1 K. Nakamura,∗1 Y. Kuboki,∗2,∗3 H. Ninomiya,∗1 Y. Shigekawa,∗1 E. Watanabe,∗1Y. Yasuda,∗1 K. Toyomura,∗1 M. Nagase,∗1 T. Yokokita,∗1,∗3 Y. Komori,∗1,∗3 H. Haba,∗3 T. Yoshimura,∗4H. Itabashi,∗5 and A. Shinohara∗1
Chemical studies of the transactinide (superheavy) elements with atomic numbers Z ≥ 104 are imperative forsystematic understanding of all the elements in the periodic table. In particular, the inﬂuence of relativistic
eﬀects on orbital electrons of superheavy elements could
cause their unique chemical properties. For chemical
experiments on superheavy elements which can be produced only by nuclear reactions, repetitive or ﬂow-type
rapid chemistry apparatus connected with a gas-jet system which rapidly transports the nuclear reaction products from the accelerator room to the chemistry laboratory (“online” experiment) is required. The chemical
properties of heavy elements are discussed on the basis of comparison of their behaviors with those of thecorresponding homologues.
We plan to apply a ﬂow-type solvent extraction apparatus, having a chemical reaction unit which shortens
the time required for equilibrium, to transactinide chemistry in order to obtain equilibrium D values for shortlived transactinide elements. Thus, we developed such asolvent extraction apparatus for the online transactinide
chemistry and determined the conditions to rapidly obtain equilibrium D values for Zr and Hf toward the extraction of 261 Rf. In addition, we carried out the online
extraction experiment as a model experiment for Rf using the developed apparatus.
First of all, we carried out the solvent extraction ofZr and Hf by the conventional shaking (batch) method
to obtain the equilibrium D values using 88 Zr and 175 Hf
tracers. The D values were determined from the concentration ratio of the tracers between organic and aqueoussolutions.
Then, we developed an online ﬂow-type solvent extraction apparatus: ﬂow Injection Solvent Extraction
apparatus for heavy elements (ISE) for rapid solvent
extraction and phase separation toward the extractionof 68-s 261 Rf. The developed extraction apparatus isequipped with a reactor tube ﬁlled with PTFE chips
to mix aqueous and organic solutions thoroughly (extraction unit; EU).1) By this unit, the diﬀusion lengthof metal complexes between the aqueous and organic
solutions decreases, which is expected to aid the rapid
achievement of equilibrium in the extraction reactions.
†∗1
∗2
∗3
∗4
∗5

Condensed from the article in Solvent Extr. Ion Exch. 38, 318(2020)
Graduate School of Science, Osaka University
National Institute of Technology, Ibaraki College
RIKEN Nishina Center
Radioisotope Research Center, Osaka University
Faculty of Engineering, Gunma University

Accelerator room

Chemistry room

Pump（Aq.）
Beam
Dissolution
apparatus

TargetHe gasKCl cluster
generator

ISEPump（Org.）
γ-raymeasurement

Fig. 1. Schematic diagram of online solvent extraction experiment for heavy elements.

For rapid phase separation between aqueous and organic
solutions, a ﬂow-type phase separation unit (PSU) using
a PTFE membrane ﬁlter (pore size: 0.8 µm) is set downstream of the EU.2) The online extraction experimentemploying the ISE was carried out using the 89g, m Zrand 173 Hf nuclides produced at the AVF cyclotron inRCNP as shown schematically in Fig. 1.
The D values obtained with ISE in 7.8 M HCl are
clearly lower than the equilibrium D values, suggesting that the equilibrium D values cannot be obtainedin 7 M HCl. When the extraction was carried out in
9.3 and 11.2 M HCl using a 30-cm-long EU packed with250–500 µm PTFE chips, the D values obtained with
ISE are all equivalent with the equilibrium values, indicating that the extraction reactions rapidly reach equilibrium state under these conditions. It was also foundthat the elution of almost all the isotopes from PSU wasaccomplished within 55 s. Based on this time information, the time taken for extraction and evaporation forα measurements in Rf experiment can be estimated tobe <2 min, which is suﬃciently fast in comparison withthe previous experiment of 261 Rf (∼100 s).
A linear relationship was observed between the logarithm of D value and the logarithm of Aliquat 336
concentration for both Zr and Hf, suggesting that theextracted chloride complex determined from the slopes(net charge) could be [MCl6 ]2− . Similar discussion canbe made for Rf, which will help to understand the chloride complexation of Rf.
References

1) H. Itabashi, Y. Mesuda, J. Flow Inject. Anal. 20, 193 (2003).
2) S. Motomizu, M. Oshima, Analyst 112, 295 (1987).

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