Effective extraction performance of a fluorous phosphate for Zr(IV) from HNO3
solution: comparison with a tri-n-butyl phosphate

Y. Ueda1,3), K. Kikuchi1,2), T. Sugita1), R. Motokawa1,3)
1): R. G. for Interfacial Reaction-Field Chemistry, JAEA2): Ibaraki Univ. 3): R. G. for Hierarchical Structure, JAEA

BeforeOrg. phase
Aq. phase

AfterExtraction
Third phaseFig. 1 Snapshot of the third phase formation.

In this contribution, we developed a fluoroalkylated
phosphate (TFP) for Zr(IV) extraction to increase the extraction
performance and prevent third-phase formation (Figure 2) [3].
Fluorous solvents such as perfluorinated alkanes have uniquechemical properties, including low toxicity, non-flammability,and immiscibility with both water and organic solutions. The
high hydrophobicity of a fluorous solvent reduces the formationof a third phase and interfacial crud.
The dependences of the Zr(IV) extraction from HNO3
solution by 0.05 M TFP and 0.5 M TBP on HNO3 concentration
were determined to compare the fluorous and conventionalorganic extraction systems. Figure 3 shows the effect of theinitial HNO3 concentration in the aqueous phase on thedistribution ratio of Zr(IV) (= [Zr(IV)]ext,eq / [Zr(IV)]aq,eq). FromOOO P OOC4F9O P OO

C4F9C4F9TFP

TBPFig. 2 Chemical structures of the fluorous phosphate (left) and theconventional organic phosphate (right).

this result, 0.05 M TFP had a much higher Zr(IV) extraction
performance than 0.5 M TBP despite the TFP concentration inthe fluorous phase being one-tenth of that of TBP. Moreover, nothird phase formed even in the high concentration-TFP system.
To verify the reason for the superior Zr(IV) extraction
performance of TFP compared with TBP, the compositions ofeach phase before and after water, HNO3, and Zr(IV) extraction
were determined. The concentrations of water and HNO3
molecules in the fluorous phase become low during the Zr(IV)extraction, indicating that water and HNO3 molecules do notpreferentially interact with TFP in contrast to TBP. We believethat the superior performance of TFP makes it suitable as analternative extractant to TBP in the Zr(IV) extraction system andto other conventional organic extraction systems.

Distribution ratio of Zr(IV)An efficient separation technology for various radionuclides
is important to reduce the amount and toxicity of radioactive
waste and to concentrate high radioactivity in small waste
volumes. The separation of metal ions such as radionuclides iscarried out by a hydrometallurgical process mainly based on asolvent extraction method. Solvent extraction is a separation
technique for concentrating and separating a certain target
component by using distribution of a solute between twoimmiscible solutions. The solvent extraction method has been
widely adopted to practical process for reprocessing spent
nuclear fuel and refining valuable metals. The extraction andseparation of Zr(IV) as a fission product from aqueous HNO3solutions has been investigated extensively because the presenceof Zr species in the tri-n-butyl phosphate (TBP)-based
reprocessing of spent nuclear fuel is problematic [1]. Zr species
are likely to form a liquid–liquid (water, oil) interfacial crud or
third phase during Zr extraction procedure by TBP from HNO3
aqueous solution (Figure 1). Formation of third phase is anundesirable process in the reprocessing of spent fuel, as it could
potentially cause safety and criticality concerns due to the highmetal concentrations. We have recently reported that a Zrloaded organic phase from liquid–liquid extraction with TBP
shows hierarchical aggregation behaviors of Zr(NO3)4(TBP)2
coordination complexes, which self-assemble into primaryclusters that coalesce further to form superclusters [2]. This
supercluster formation portends the formation of third phase andinterfacial crud. However, there are still few proposals fordevelopment of the extraction system with a new extractant that
does not suffer from these problems.

104

TFP

103
102
101

TBP

100
10−110−210−30.1

110[HNO3]aq,in (mol dm−3)

Fig. 3 Effect of HNO3 concentration on the distribution ratio ofZr(IV) by TFP and TBP. [TFP] = 0.05 M in perfluorohexane, [TBP]= 0.5 M in n-octane, [Zr(IV)] = 0.01 M, [HNO3] = 0.1–15.6 M.

References[1] T. V. Healy et al., Trans. Faraday Soc. 52, 633 (1956).
[2] R. Motokawa et al., ACS Cent. Sci. 5, 85 (2019).
[3] Y. Ueda et al., Solvent Extr. Ion Exch. 37, 347 (2019).