Research Group for Interfacial Reaction Field ChemistryGroup Leader: Bernd GRAMBOWMembers: KOZAI Naofumi, NAGANO Tetsushi, SHIMOYAMA Iwao, AOYAGI Noboru,TANAKA Kazuya, NANKAWA Takuya, OKAMURA Hiroyuki, SUGITA Tsuyoshi, Ibrahim
MAAMOUN (PD), Huiyang MEI (PD)Our research objectives are to explore novel chemical
reactions of aqueous species of elements at liquid-solid andliquid-liquid interfaces to contribute to environmental chemistry,actinide chemistry, and waste treatment & disposal. Moreconcretely, we focus our research on elucidation ofenvironmental radionuclide migration and radioactive wastetreatment. The research on elucidation on environmental
radionuclide migration has two research fields, Fukushima andNingyo-toge. Research on the environmental aspects of the
Fukushima issues includes circulation of radiocesium (Cs) in
Fukushima forest and decontamination of contaminatedsubstances. Research on Ningyo-toge includes chemistry ofuranium and radium in soil, rock, and groundwater in thecontext of environmental safety. Research and development onradioactive waste treatment includes development ofbreakthrough technologies particularly for difficult-to-treatelements.
Research on radiocesium migration in the terrestrial
environment
Since the Fukushima Daiichi nuclear power plant (1F)
accident, our group has been investigating Cs migration in theterrestrial environment, particularly in the forest environment.
The forest environment is a very complex system, wherephysicochemical characteristics of inorganic substances(minerals, ions) are influenced by numerous living substances(microorganisms including mushrooms, insects, plants, and soon) and organic substances originated from those living
substances. This complexity makes the elucidation of Csmigration in the forest environment difficult. Mushroom
generally has a high Cs accumulating capacity. However, the Csaccumulation mechanisms, such as why mushroom accumulatesCs and what will become of the accumulated Cs after the deathof mushroom, have not been clarified. We investigatedaccumulation of Cs by shiitake mushroom and leach of theaccumulated Cs after the death of shiitake fruit bodies [1]. We
revealed that Cs is present at a constant ratio to potassium,
which is an essential element and has a chemical nature similar
to Cs, in any part of the fruit body. After the death of theshiitake fruit body, most of the Cs accumulated in the fruit
bodies were leached into water. Our results strongly suggest thatshiitake has no tissues (organic substances) that strongly bind toCs and that by being exposed to rain after the death of the fruit
body Cs is leached out of the cells and returns to soil. These
results are consistent with our result published in 2020 that thebinding between the Cs accumulated in some trees and theirtissues (organic substances) is weak [2]. It is generally
considered that when Cs ions reach to soil the Cs is tightly fixed
to clay minerals in soil and becomes immobile. On the otherhand, plants and mushrooms absorb Cs from soil. This
inconsistency has not received attention. We investigatedreaction of a clay mineral and siderophore, which is an organic
iron chelating substance and produced by many of soil bacteria,
in terms of Cs behavior in soil [2]. The siderophore, which wasproduced by an endophytic bacteria isolated from the root ofclover, selectively dissolved the biotite crystals and the Cs fromthe broken edge of the biotite. Our findings suggest that Cs
circulates in the forest environment as soil microorganisms
dissolve the Cs little by little but constantly from clay minerals,
plants and mushrooms absorb the dissolved Cs, the absorbed Cs
is released from the plants and mushrooms after their death, andthe released Cs is fixed to the soil.
As for the research on Ningyo-toge, a synchrotron radiation
analysis of hydrated barium ion, which has similar chemical
characteristics to radium, was performed as a preliminary study
to evaluate the applicability of our approach to radium analysis.
The analytical results matched the ab initio molecular dynamics
simulation result for hydrated barium ion [4]. Following thissuccess, we started planning of radium analysis. The iron plaque(deposit) formed on the root of Phragmites australis that grows
in a mill tailing pond of the Ningyo-toge environmental
engineering center accumulated uranium [5]. The iron plaque,probably formed by microbial activity of root-endophytic
bacteria of P. australis, may prevent accumulation of uranium inthe upper part of the plant because uranium is not detected there.
Research and development of radioactive waste treatment
The main objective radionuclides of this research are anionicradionuclides with long half-lives (79Se, 99Tc, and 129I) becauseof their difficulty in stable confinement in waste forms and highmobility in the environment. In the contaminated water
treatment facilities of 1F, the 129I in the contaminated water isbelieved to be mainly removed by activated carbon (AC).
Groundwater is flowing into 1F, and groundwater generally
contains organic substances such as fulvic acid. We revealed
that a fraction of the iodate (IO3–) adsorbed on AC changes toiodide (I–) by fulvic acid [6]. The adsorptivity of I– to AC islower than that of IO3–. Our results suggest that during thestorage of spent AC a fraction of the IO3– on AC changes to I–
and a fraction of I– desorbs from the AC.
We also reported that alkaline geopolymer is superior toconventional Portland cement as solidification method for thesewage sludge ash contaminated with Cs [7] and revealed thatthe metal organic framework (MOF) that is easily synthesizedusing terbium oxalate has a high selectivity and adsorption
capacity for Pb2+ (see Highlight) [8].
References[1] F. Guido-Garcia et al., Chemosphere, 279, 130511 (2021).
[2] K. Tanaka et al., Sci. Total. Environ., 755, 142598 (2021).
[3] T. Kimura et al., Chemosphere, 276, 130121 (2021).
[4] A. Yamaguchi et al., Chem. Phys. Lett., 780, 138945 (2021).
[5] Y. Nakamoto et al., Minerals, 11, 1337 (2021).
[6] T. Kato et al., J. Nucl. Sci. Technol., 59, 580 (2022).
[7] N. Kozai et al., J. Hazard. Mater., 416, 125965 (2021).
[8] T. Nankawa et al., Bull. Chem. Soc. Jpn., 95, 825 (2022).