Oral Presentation International Solvent Extraction Conference 2025

Extraction mechanisms in fluorous and organic extraction systems and structuring extractants in bulk extraction phases (122690)

Yuki Ueda 1 , Cyril Micheau 1 , Kazuhiro Akutsu-Suyama 2 , Kohei Tokunaga 3 , Masako Yamada 4 , Norifumi L. Yamada 4 , Damien Bourgeois 5 , Ryuhei Motokawa 1
  1. Japan Atomic Energy Agency, Tokai-mura, Naka-gun, IBARAKI, Japan
  2. Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society, Tokai, Ibaraki, Japan
  3. Ningyo-toge Environmental Engineering Center, Japan Atomic Energy Agency, Tomata, Okayama, Japan
  4. Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan
  5. Institut de Chimie Séparative de Marcoule, Marcoule, Bagnols-sur-Cèze, France

The extraction of Zr(IV) as a major fission product from aqueous HNO3 solutions have been investigated extensively because the presence of Zr in the tri-n-butyl phosphate (TBP)-based PUREX process for reprocessing spent nuclear fuel is problematic.[1] We have recently shown that a Zr-loaded organic phase from liquid–liquid extraction with TBP shows hierarchical aggregation behaviors of Zr(NO3)4(TBP)2 coordination complexes, which self-assemble into primary clusters that coalesce further to form superclusters. This supercluster formation portends the formation of the third phase and interfacial cruds.[2] In this study, we develop a fluoroalkylated phosphate, tris(4,4,5,5,6,6,7,7,7-nonafluoroheptyl) phosphate (TFP), for Zr(IV) extraction to increase the extractability and prevent third-phase formation. Fluorous solvents have excellent chemical properties and immiscibility with both water and organic solutions.[3] Considering these properties, the hierarchical aggregating behaviors of Zr(IV) and the highly hydrophobic fluorous extractant should be different from that of Zr(IV) with TBP, and this may reduce the formation of a third phase and interfacial crud. We investigated the extraction performance and mechanism of TFP extraction of Zr(IV) from HNO3 solutions into perfluorohexane and compared them with the conventional organic extraction system using tri-n-alkyl phosphate (TAP) in n-hexane.

The extraction experiments were carried out by the batch method. The fluorous and organic phases were 0.05 M TFP in perfluorohexane and 0.50 M TAP in n-hexane, respectively. The aqueous phase was prepared by mixing the 1.12 M Zr(IV) stock solution and the 15.6 M HNO3 solution to obtain the 0.01 M Zr(IV) and the 0.1–15 M HNO3 solutions. Equal volumes of both phases were mixed at 25°C and 1800 rpm. After phase separation, the Zr(IV), HNO3, and H2O concentrations were measured by inductively coupled plasma mass spectrometer, ion chromatography, and Karl-Fischer titration, respectively. The distribution ratio of Zr(IV) was calculated by the mass balance. In addition, 31P nuclear magnetic resonance, small-angle neutron scattering, and neutron reflectometry were used to observe the bulk and interface structure of the extracting phases after Zr(IV) extraction. Despite TFP concentration being one-tenth of that of TAP, the 0.05 M TFP had a much higher Zr(IV) extraction performance. Moreover, no third phase formed, even as the concentration of TFP was increased. To verify the reason for the superior Zr(IV) extraction performance of TFP, the compositions of each phase before and after water, HNO3, and Zr(IV) extraction were determined using both TFP and TAP. The concentrations of water and HNO3 molecules in the fluorous phase lowered during Zr(IV) extraction, indicating that, unlike with TAP, water and HNO3 molecules do not preferentially interact with TFP. In this work, a new fluorous phosphate extractant, TFP, was synthesized and its extraction performance for Zr(IV) from HNO3 aqueous solution was evaluated. The Zr(IV) extraction strength of TFP in the perfluorohexane was much higher than that of TAP in n-hexane. We believe that the superior performance of TFP in perfluorohexane makes it suitable as an alternative extractant to TAP in the Zr(IV) extraction system and to other conventional organic extraction systems.

  1. [1] Blazheva, I. V.; Fedorov, Y. S.; Zilberman, B. Y.; Mashirov, L. G. (2008). Extraction of Zirconium with Tributyl Phosphate from Nitric Acid Solutions. Radiochemistry, 50, 256–260.
  2. [2] Motokawa, R.; Kobayashi, T.; Endo, H.; Mu, J.; Williams, C. D.; Masters, A. J.; Antonio, M. R.; Heller, W. T.; Nagao, M. (2019). A Telescoping View of Solute Architectures in A Complex Fluid System. ACS Central Science, 5, 85–96.
  3. [3] Gladysz, J. A.; Emnet, C. (2004). Fluorous Solvents and Related Media. In Gladysz, J. A., Curran, D. P., Horváth, I. T. (Eds.). Handbook of Fluorous Chemistry (pp 11–23). Weinheim: Wiley-VCH.
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