Photon Factory Activity Report 2017 #35 (2018)

BL-27B/2016G557

Local Structural Analysis of Rare Earth Complex in the Adsorbents for Extraction
Chromatography
Yuya Katai 1, Sou Watanabe 2, Hirohide Kofuji 2, Ryoji Abe 3, Tomoaki Sakurai 3, Tsuyoshi Arai 3,and Haruaki Matsuura 1
1

Department of Nuclear Safety Engineering, Tokyo City University, 1-28-1, Tamazutsumi,
Setagaya-ku, Tokyo, 1588557, Japan
2
Japan Atomic Energy Agency, 2-4, Shirakata, Nakagun,Toukai-mura, Ibaraki, 3191195, Japan3
Shibaura Institute of Technology, 3-7-5, Toyosu, Koto-ku, Tokyo, 1358548, Japan

2 Experiment
The adsorbent was prepared by impregnating CMPO
(octyl(phenyl)-N,N-diisobutylcarbamoylmethyl)phosphineoxide)and HDEHP (Bis(2-Ethylhexyl)hydrogenphosphate) into the polymer with molar ratio of 1 to 1. Eu
in 3 mol/L nitric acid solution was loaded into theadsorbent through column operation. The adsorbent wasmixed with DTPA solution at various pH which is aneluent for selective MA stripping, and then shaken for 3 h.
The adsorbent washed with the DTPA solution wassupplied to Ln washing experiments. In order to examine
applicability of several carboxylic complex solutions forthe washing solution, lactic acid, oxalic acid and citricacid solution with various pH were used for batch-wisewashing operation. The adsorbents loading Eu, washedwith DTPA and with DTPA and the wash solutions weresupplied to EXAFS analysis. Eu LIII edge transmission
EXAFS measurements on the adsorbents were carried out.
An EXAFS oscillation was extracted using the cubic
spline method and the structure function was obtained by
the Fourier transformation. Structural parameters werederived from fitting based on the EXAFS equation.

3 Results and Discussion
The citric acid solution with high pH showed excellent
performance for the Ln washing. By EXAFS of DTPA
washed adsorbents at various pH conditions, coordination
number of the nearest oxygen around an europium was 9
at pH=1 and decreases to 6 with increasing pH up to 3 asshown in Fig. 1. This fact is considered to suggest that
dominant europium complex after washing with DTPA at
pH=1 is Eu(NO3)3(CMPO)n, while at pH=3 isEu(H(DEHP)2)3. EXAFS of citric acid washed adsorbents
at various pH conditions showed that the coordination
number around Eu decreases with increasing pH. This
result must be due to weakening in Eu-extractant
interaction with increasing of the pH of citric acid wash
solution. These features are reasonably explained byelution behavior of europium by the citric acid. Based on
the structural analysis, a promising flow-sheet wasdesigned. Demonstration through column separation
experiments on simulated and genuine high level liquid
wastes will be carried out in near future.
EXAFS analysis on complex formed in the adsorbent for
the extraction chromatography was shown to be one of
powerful tools for design a flow-sheet. Demonstration of
the optimized flow-sheet based on this study will be
carried out soon.
Eu-O coordination number

1 Introduction
Recovery of trivalent minor actinides (MA: Am andCm) from high level radioactive liquid wastes is an
important task for reduction in volume and potential
hazard of the final wastes, and an extraction
chromatography has been under development as apromising technology for selective MA recovery. In thisprocess, specific adsorbents which keep extractant
molecules in the polymer coating over the porous silica
matrix are used for column chromatographic separation.
In a current promising flow-sheet, selective MA strippingfrom an adsorbent was achieved. However, washing outof loaded lanthanides (Ln) in the adsorbent after the MA
recovery is required for repeated use of the adsorbent. To
find out the best Ln washing condition effectively,extended X-ray absorption fine structure analysis oncomplexes of rare earth elements formed the adsorbents
were carried out.

DTPAEU

987
6
5
1

23pH
Fig. 1: Coordination number variation of O around an Eu ofadsorbent after elution treatment by DTPA at various pH 1 – 3.

* hmatuura@tcu.ac.jp