Research Group for Interfacial Reaction Field ChemistryGroup Leader: Bernd Grambow
Members:Naofumi
Kozai,Naganawa, Tetsushi Nagano, Fuminori Sakamoto, Iwao
グループ名, Times
New Roman,
14 point,Hirochikabold
GL、メンバー名, Times
New Roman,
12pointsKojiro Shimojo, Kazuya Tanaka, Takuya Nankawa, Hiroyuki
Shimoyama,
NoboruAoyagi,Okamura, Tsuyoshi Sugita, Kohei Tokunaga, Yuki Ueda, Fabiola Guido-Garcia

The research objectives of this group are to explore novel
chemical reactions of aqueous chemical species at liquid-solidand liquid-liquid interfaces to contribute to environmental
chemistry, actinide chemistry, and waste treatment. For the yearof 2018, we report progress in uranium (U) recovery techniqueusing an emulsion flow system [1] and in environmental
migration of radiocesium in Fukushima [2],[3].
Continuous removal of U from U-containing wastewaterusing an organic phase-refining-type emulsion flow
extractor
At Ningyo-toge Environmental Engineering Center, JAEA,
a large quantity of uranium-containing wastewater (UW) has
been generated from the decontamination of spent centrifuges.
For selective U removal from the UW, we have introduced acontinuous liquid–liquid extraction method using an “emulsionflow” (EF) extractor, wherein the EF is generated by spraying
fine droplets of extractant-containing organic phases intoaqueous phases. However, the removal performance of U has
gradually deteriorated in the conventional EF system without amechanism of refining organic phase.
We have developed a new EF system equipped with arefining column for clean-up of used organic phase. In thisapparatus, the organic phase is circulated between the extraction
and the refining columns. During the circulation, U in the feedsolution is extracted into the organic phase in the extraction
column and stripped into the refining aqueous solution in therefining column. In this manner, the organic phase iscontinuously refined as it is being circulated (Fig. 1).
The new EF system was applied to the continuous removalof U from the simulated UW. The organic phase used in thissystem is Shellsol D70 solution containing tri-n-octylamine and2-ethylhexanol, which is effective in selective extraction of U
from dilute sulfuric acid solutions. The feed volume of the UW
was 5 L, which was 10 times larger than that of the organicsolution. A comparative experiment was carried out under non–refining condition using the conventional EF system. As a result,the U removal rates remained almost constant at ~90% under
the refining condition while it gradually decreased from ~90%
to ~36% under the non-refining condition (Fig. 1). The
elemental analysis of the organic phases after the end of theexperiment showed that the U in the organic phase under therefining condition decreased significantly compared to that
under the non-refining condition. As a result, the newly
developed organic phase–refining–type EF system is considered
to be superior to the conventional one using the extraction
column alone for the treatment of a large volume of UW,
because the refining column works effectively in terms of
preventing the deterioration of the removal performance.
Distribution and migration of Fukushima-derived
radiocesium in the environment
In order to evaluate migration of radiocesium derived fromthe accident at Fukushima Daiichi Power Plant in environment
based on a comparison of radiocesium to stable Cs, we haveinvestigated size-fractioned samples of riverbed sediments
collected at two sites, a pasture and Kuroiwa in the Abukuma

River system in Fukushima Pref. The size distributions of K, Rband stable Cs reflected the mineralogy of sediments, whereprimary host minerals for these alkali elements would be biotite,
K-feldspar and clay minerals. Silt-size fractions contained highstable Cs and radiocesium concentrations possibly due toadsorption on clay minerals. Overall, the size distributions ofstable Cs and 137Cs were similar in the sediments (Fig. 2),
suggesting that radiocesium released by the Fukushima accident
was distributed into each particle size fraction in response to thedistribution of the stable Cs that was governed by mineralogicalcomposition [2].
Surface soil samples collected from Kawamata, Fukushima Pref.
were leached with natural seawater, diluted seawaters, andultrapure water (PW) to observe the effect of the ionic strength
on leaching ratios of 137Cs [3]. Overall, seawater and diluted
seawater gave higher leaching ratios than PW. For long-term
experiments (223 days), more than 15% of total 137Cs in the soil
sample was leached with seawater. While about 9% of the total
137Cs was leached with 1:1 diluted seawater, less than 1% of thetotal 137Cs was leached with PW over the 223 days.
Radiocesium fixed in clay minerals of soil and sediment would
be partially extracted by seawater after their transport to theocean via rivers.
Fig. 1 Outline of organic phase-refining-type EF extractor (left) and U

removal rate with and without refining organic phase (right).

Fig. 2 Size distributions of stable Cs (left) and radiocesium (right) inriverbed sediments collected in Fukushima [2].

References[1] T. Nagano et al., Anal. Sci., 34, 1099 (2018).
[2] K. Tanaka et al., Geochem. J., 52, 173 (2018).
[3] A. Sakaguchi et al., Geochem. J., 52, 186 (2018).