Research Group for Interfacial Reaction Field ChemistryGroup Leader: Bernd GRAMBOWMembers: KOZAI Naofumi, NAGANAWA Hirochika, NAGANO Tetsushi, SAKAMOTOFuminori,
SHIMOYAMAIwao,
グループ名, Times
New Roman, 14 point,bold AOYAGI Noboru, TANAKA Kazuya, NANKAWA Takuya,
GL、メンバー名, Times
New Roman,
12points Tsuyoshi, UEDA Yuki, Fabiola G. GUIDO, HARUMAOKAMURA
Hiroyuki,
SUGITA
Toshikatsu

The research objectives of this group are to explore novel
chemical reactions of aqueous species of elements at liquidsolid and liquid-liquid interfaces to contribute to environmental
chemistry, actinide chemistry, and waste treatment.
More concretely, we focus our research on elucidation on
environmental radionuclide migration and radioactive wastetreatment. The research on elucidation on environmental
radionuclide migration has two research fields, Fukushima andNingyo-toge. Researches on the environmental aspects of theFukushima issues include circulation of 137Cs in Fukushima
forest and decontamination of contaminated substances.
Researches on Ningyo-toge include chemistry of uranium andradium in soil, rock and groundwater in the context withenvironmental safety. Research and development on radioactive
waste treatment includes development of breakthroughtechnologies particularly for difficult-to-treat elements.
Migration 2019 conference
The 17th International Conference on the Chemistry andMigration Behavior of Actinides and Fission Products in thegeosphere was held from September 15 to 20, 2019 in Kyoto.
Key subjects were the geological disposal of radioactive waste
in Japan and the remediation of the Fukushima Daiichi NPS site.
The MIGRATION conference series is led by an international
steering committee including Dr. Grambow, the GL of thisgroup, and has provided an international forum for the timely
exchange of scientific information on chemical processes
controlling the migration behavior of actinides and fission
products in natural aquifer systems. Experimental investigations
and predictive modelling of these processes are the main topicsof the conferences. Therefore, this conference is a crucial place
for this group to present achievements and exchange opinions.
This group made ten first authored presentations and six coauthored presentations. Subjects presented by this groupmembers were the formation of giant cerium(IV) clusters, thecomplexation of actinides with borate, the environmental issues
at the uranium mine Ningyo-toge, the database forthermodynamics of actinides, the microbial effects on simulated
nuclear fuel debris, the uptake of radiocesium by mushrooms,
radiocesium migration in soils, the role of siderophores inradionuclide mobilization from minerals, radiocesium in sewage
sludge ash, the use of chloride salts for soil decontamination athigh temperature, the radium removal from uranium mining
waste water, and the removal of radionuclides by coprecipitation
with barite. GL Grambow presented an invited talk “Towards
geological disposal in Japan and remediation of the Fukushima
Daiichi NPS site: Research strategy in the global context.
Research on radioactive waste treatment
The main objective radionuclides of this research are anionicradionuclides with long half-lives. They are 79Se, 99Tc, and 129I.
Most of the other fission product radionuclides are cations inacid aqueous solution. Numerous methods have been proposed
to recover or inorganically fix (solidify) cationic radionuclides
since most of natural and synthetic substances have negative

charges. It is, however, very difficult for those anionicradionuclides, particularly Tc and I. These two elements arepresent as monovalent anions (TcVIIO4-, I-, IO3-) under wide
environmental conditions, and their stable complexes andinorganic solids are hardly known.
To obtain basic knowledge on TcVII adsorption on inorganic
substances, we used ReVII as analogue of TcVII and investigatedadsorption on two representative materials with positive charges(hydrotalcite-like layered materials). We found that the ReVII
was adsorbed reversibly (anion exchange) in the form of outersphere complexes [1, 2]. These results are in harmony withprevious knowledge and suggest that adsorption is not
appropriate for inorganic fixation of anionic radionuclides when
considering instability of adsorbed radionuclides toward anion
exchange. Considering this fact, our group have been working
on recovering anionic radionuclides from wastewater into theinside of inorganic solid (host phase) by coprecipitation andthen stabilizing the host phase to internally fix anionicradionuclides. We reported a coprecipitation method forrecovering Se anions in barite (barium sulfate) which has asignificantly low solubility [3]. We also found coprecipitation
methods for recovering iodate (IO3-) in barite and ettringite(hydrous calcium aluminum sulfate mineral) [4, 5]. Our current
efforts are focused on post coprecipitation method to stably
confine iodine in barite structure and performance evaluation ofsolidified bodies (waste form) containing iodine-recovered
barite. TcVII coprecipitation with barite is difficult. Instead, we
have been investigating an alternative method to use TcVII
reduction and coprecipitation in combination.
In terms of radionuclide extraction from waste liquids,
selectivity and capacity for objective element have been thecritical factors in developing new extraction agents. Our grouphas been proposing several new extracting agents in the same
approach. So-called “the third phase” formation is anothercrucial problem in extraction process. In the extraction process
at a high metal loading, the third phase containing extractant andmetal ions at high concentrations often forms at liquid-liquidinterface, which obstructs stable operation. We recently havedeveloped a new extraction system that hardly extracts nitricacid, so that the third phase does not form in the system.
Because of this nature, the new system shows high metalextractability far superior to conventional extraction system in awide nitric acid concentration range [6] (see Highlight).
References[1] K. Tanaka et al., J. Porous Mater., 26, 505-511 (2018).
[2] K. Tanaka et al., Appl. Clay Sci., 182, 105282 (2019).
[3] K. Tokunaga et al., Environ. Sci. technol., 51, 9194 (2017).
[4] K. Tokunaga et al., submitted.
[5] B. Guo et al., J. Hazard. Mater., in press.
[6] Y. Ueda et al., Solvent Extraction and Ion Exchange, 37, 347(2019)