Photon Factory Activity Report 2005 #23 Part B (2006)
Chemistry

27B/2003G285

XAFS analysis of UO2(NO3)x(TcO4)2-x(TBP)2
Shinichi SUZUKI*1, Tsuyoshi YAITA2, Yoshihiro OKAMOTO2, Hideaki SHIWAKU2
1JAEA, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
2
JAEA, Kouto, Sayo-cho, Sayo-gun Hyogo 679-5198, Japan
Introduction
In the nuclear fuel re-processing, technetium exists as
per-technetate ion. The per-technetate ion iscomparatively large tetrahedral structure which consistsof four oxygen, while the effective charge iscomparatively smaller than other anion. Therefore, it isextracted in ion pair as a pertechnetic acid by tri-butyl
phosphate(TBP) easily. Furthermore, the per-technetateion is co-extracted with counters ions such as UO22+, Pu4+
and Zr4+ with TBP. However, there is few reported about
structural analysis of these co-extracted complexes until
now. In this study, the structural analysis of the coextracted complexes were performed about Tc-complexes
UO2(NO3)x(TcO4)2-x(TBP)2 [1].
Experimental
The technetium samples were made as following
procedure. 1 ml of n-dodecane as an organic solvent
containing 30 % tri-butyl phosphate was shaken with thesame volume of the various nitric acid containing 40 mMof UO22+ with about 0.7 M of TcO4-. After centrifugation,
0.45 ml of the organic solution was separated to use as asample. 0.45 ml of Tc-U-TBP complex solution wasenclosed in polyethylene tube. The XAFS measurement
carried out at beam line BL27B. The absorption edges
were 17.16 keV for U(LIII), and 21.05 keV for Tc(K).
Results and Discussion
The radial structural functions of Tc-K XAFS for TcU-TBP complex in dodecane prepared by the solvent
extraction method is shown in Fig.1. The first peak in thesample is attributed to the four oxygen atoms of TcO4- ion.
The bond distance of Tc-O, i.e. about 1.74 Å, agrees wellwith the previous data [2]. Generally, technetium isfurther extracted in the presence of U(VI) ion in thesolvent extraction with TBP. Therefore, technetium isregarded to behave as a counter ion in the extraction ofuranium. Accordingly, the peaks around 3.2 Å (in RSF)
can be attributed to the Tc-U interaction. The curve fitting
for the UO2-TcO4-NO3-TBP complexes of Tc-K XAFS isalso shown in Fig.1. The bond distance of Tc-O and Tc-U
are about 1.74 Å and 3.59 Å, respectively. These
structural analysis data suggest that TcO4- ion coordinates
to uranium with bidentate fashion instead of a nitrate ion
in the Tc co-extraction system. The comparison of radial
XAFS
forstructuralfunctionsofU-LIIIUO2(NO3)2(TBP)2
andUO2(TcO4)(NO3)(TBP)2,UO2(NO3)2(H2O)2 are shown in Fig.2. The U-O(O-Tc)
and U-Tc of UO2(NO3)(TcO4)(TBP)2 are also confirmed,
and a significant evidence of TcO4- for direct coordination
to UO22+. The distance of U-Tc is 3.60 Å, which wellagrees with the Tc-K XAFS result. The interaction ofuranium are mainly 5, U=Oaxial, U-Oeq1 (O=P), U-Oeq2(O2-NO), U-Oeq3 (O-Tc), and U-Tc. The bond distance ofthe U-Oeq3 (O-Tc): 2.97 Å is longer than the U-Oeq2 (O2NO): 2.51 Å and U-Oeq1 (O=P): 2.31 Å. Therefore, TcO4would be weaker interaction than the other oxygen.

N=4R=1.74 Å
σ2=0.002 Å2
N=1
R=3.59 Å
σ2=0.005 Å2Fig.1. The radial structural functions and the curve
fitting of Tc K-EXAFS spectra on the basis of UO2TcO4-NO3-TBP model.
* The N, R, σ2 present the coordination number, bonddistance, and debye-waller factor, respectively.
**The phase shifts were not corrected.

123Fig.2. The comparison of radial structural functions ofTc-ligand complexes.
1 : UO2(NO3)(TcO4)(TBP)2, 2 : UO2(NO3)2(TBP)2,
3 : UO2(NO3)2(H2O)2*The phase shifts were not corrected.
References[1] S.Suzuki et al., Physica Pcripta, T115, 306(2005).
[2] P.G.Allen et al., Radiochimca. Acta, 76,77(1997)*suzuki.shinichi@jaea.go.jp

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