Takumi.Saito – Page 4 – Saito's group webpage

Research equipment

ICP-MS (Inductively Coupled Plasma Mass Spectrometry): Agilent 7500 cx ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry): Shimadzu ICPS-7510 Field-flow fractionation: Postnova Analytics AF2000 FOCUS UV/Vis detector Fluorescence detector RI detector Automated titrator Wallingford Titrator Metrohm Titrand UV/Vis spectrometer: Shimadzu UV-2700 Fluorescence spectrometer: JASCO FP-8300 Infrared spectrometer: JASCO FTIR-6600 MCT detector ATR unit (diamond, single reflection) Diffuse reflection unit Ion chromatography: Metrohm IC930 CO2 suppressor Chemical suppressor TOC: Shimadzu TOC-V CSH Thermal analysis (TG/DTA) Centrifuge Glovebox Laser spectroscopy systems

Long-term desorption of radioactive Cs from soilsLong-term desorption of radioactive Cs from soils

Introduction Vast areas of north-eastern regions of Japan has been contaminated by radionuclides released from the accident of the TEPCO’s Fukushima Dai-ichi nuclear power plants. In particular, radioactive cesium, namely 137Cs, cause many problems due to its relatively long half-life (30.1 years), including decontamination and the management of contaminated soil wastes. To settle such problems, we need to know long-term behaviors of radioactive Cs in soils. Cesium is reported to be strongly fixed micaceous to so-called frayed edge sites (FES) in minerals in soils by interlayer collapse. Nevertheless,the long-term desorption behaviors is of great importance, which is not yet fully understood in terms of the mechanisms, partly because of its slowness and also of the existence of re-sorpton. In this research, we performed the long-term desorption experiments of 137Cs and 133Cs from the real contaminated soils in the presence of varying concentrations of competing cations. The resorption of desorbed Cs was diminished by adding cation-exchange resin as an adsorbent. Experimental The contaminated soils collected in Fukushima prefecture after 40 days since the accident were used. Soils were suspended in dilute KCl solution together with a dialysis bag containing cation exchange resins (Dowex 50w-X8，K+ form).The dialysis bags were exchange 10 times in 3 months with new ones. 133Cs and 137Cs released from the soils and captured by the resigns were quantified […]

Article accepted in J. Environ. Radioact.

An article by our MC. student, Mr. Murota, has been accepted in J. Environ. Radioact. The title is “Desorption kinetics of cesium from Fukushima soils”. Murota, K., Saito, T.*, Tanaka, S., “Desorption kinetics of cesium from Fukushima soils”, J. Environ. Radioact. 153, 134-140 (2016).

Highlighted in the blog of Environ. Sci.: Processes Impacts, RSC

Our article has been highlighted in the blog of Environ. Sci.: Processes Impacts, RSC. Saito, T.*, Terashima, M., Aoyagi, N., Nagao, S., Fujitake, N., Ohnuki, T., “Physicochemical and ion-binding properties of highly aliphatic humic substances extracted from deep sedimentary groundwater”, Env. Sci. Process. Impact 17, 1386-1395 (2015). Open access

Selected for the cover art of JAAS, RSC

Our article has been selected as the cover art of JAAS, vol. 3o (Journal of Analytical Atomic Spectrometry), Royal Society of Chemistry. Research overview Saito, T.*, Hamamoto, T., Mizuno, T., Iwatsuki, T., Tanaka, T., “Comparative study of granitic and sedimentary groundwater colloids by flow field flow fractionation coupled with ICP-MS”, J. Anal. At. Spectrom. 30, 1229-1236 (2015). Open access

Speciation of radioactive Cs in Fukushima soils

Radioactive cesium (137Cs) released from the accidence of the Fukushima Dai-ichi nuclear power plant contaminated areas of the eastern part of Japan, particularly Fukushima prefecture and has affected the life of local residents in many ways. During the release events, 137Cs (b.p. 678˚C) was emitted to the atmosphere as CsI in aerosols. After a couple of years soil is likely the most significant reservoir for it. As 137Cs emits 652 keV γ-ray, 137Cs in top-layers of soils may contribute to external exposure of local residents and biospheres. It can be absorbed by plants from contaminated soils, which may lead to internal exposure. Thus, It is of great importance to understand behaviors of 137Cs. In this research, we’ve evaluated the geochemical and grain-size distribution of 137Cs in contaminated soils sampled in Fukushima Prefecture after the accident. The obtained results have been also compared with those of stable cesium (133Cs) to infer the variation of the geochemical distribution in the near future. 137Cs are most extracted to the acid-digestible factions and the extraction residues. It is also found that 137Cs is associated with relatively small silt and clay grains, which are rich in micaceous clay minerals and kaolins according to X-ray diffraction. We’ve found positive correlation between 137Cs content in each fraction and the amount of micaceous minerals, suggesting crucial roles of the clay minerals on […]

Speciation analyses by laser fluorescence spectroscopy

Time resolved laser fluorescence spectroscopy (TRLFS) is the analytical technique which observes de-excitation processes of excited fluorophore created by short-pulsed laser. TRLFS data of a fluorescent metal ion includes shape of emission spectrum its temporal decay These information reflects the number of allowed transitions and their probabilities competitive non-fluorescent de-excitation pathways Thus, the spectral shape will change when a fluorescence metal coordinates with a ligand and changes its energy levels and/or associated transition probabilities due to variation of the symmetry around it. Similarly, fluorescence decay lifetime will vary when a ligand around the central metal ion is displaced by another ligand, as de-excitation pathways change. We can use these changes in TRLFS data to probe reactions with a fluorescent metal ion and estimate its structural information. As good approximation, For instance, Eu3+, a chemical homologue of trivalent actinides such as Am3+ and Cm3+, has the energy diagram as in Figure 1 and the emission spectrum as in Figure 2. Its decay lifetime is around 110 μsec. Three major peaks in Figure 2 corresponds to the transitions from the 5D0 states to the 7F1，7F2，and 7F4 states. Upon complexation with acetate ligand, the spectrum changes in Figure 3. Particularly, the peak around 620 nm due to so-called hyper-sensitive transition, 5D0 → 7F2, is significantly enhanced. An overtone of OH vibration of water molecule provides an efficient pathway for excited Eu3+; the […]

Modeling the interaction of metal ions with mineral surfaces and natural organic matters

In order to estimate to understand environmental behaviors of radionuclides and toxic metal ions, we need to construct and extrapolate reaction models, which can describe changes of their speciation, from the results of detailed reaction studies and molecular-scale structural information. Such mechanistic models could help us to improve reliability of safety assessment of nuclear disposal and to develop efficient decontamination strategies. In our group, we are pursuing model development of sorption/binding interactions of metal ions and mineral surfaces or metal ions and natural organic matters. Possible effects of the interaction between mineral surfaces and natural organic matters on metal uptake are also of our great interests. Identifying adsorption structures by X-ray absorption spectroscopy and density function theory simulation X-ray absorption spectroscopy, especially extended X-ray absorption fine structure (EXAFS) analysis, is a power analytical tool, which can be applicable for structural determination around a central metal ion in amorphous samples and sorption or solution samples that lack long-range orders. The applicability of EXAFS can be further imporved, if it is combined with molecular-scale simulations such as density functional theory calculation. In this research we’ve identified possible adsorption structures of hexavalent uranium (uranyl, UO22+) on gibbsite (α-Al(OH)3) surface, which is a representative Al-containing mineral and a model for edge sites of alumino-silicate clay minerals. Hattori, T.*, Saito, T., Ishida, K., Scheinost, A. C., Tsuneda, T., Nagasaki, […]

Comparative study on deep groundwater colloids

Mobility of elements in soil and aquatic environments are regulated not only by complexation with simple ligands with low molecular masses, but also by formation of or sorption to nano-sized inorganic or organic colloids or macromolecules. In this research we have determined and compared the size distribution and elemental composition of various elements in granitic and sedimentary deep groundwater by flow-field flow fraction (Fl-FFF) hyphenated with ICP-MS. Fl-FFF is a non-invasive chromatographic size fractionation technique. Thanks to the selectivity on both size and elemental composition of colloids, we have successfully analyzed heterogeneous natural colloids in the deep groundwater. This research was conducted under collaboration with Radioactive Waste Processing and Disposal Research Department, JAEA. This research was partly supported by the Ministry of Economy, Trade and 15 Industry (METI), Japan, and “Grant-in-Aid for Young Scientists (B)” (Grant No. 25820446), the Japan Society for the Promotion of Science. Saito, T.*, Hamamoto, T., Mizuno, T., Iwatsuki, T., Tanaka, T., “Comparative study of granitic and sedimentary groundwater colloids by flow field flow fractionation coupled with ICP-MS”, J. Anal. At. Spectrom. 30, 1229-1236 (2015).

Natural organic matters in deep groundwater

Natural organic matters (NOMs) such as humic substances (HSs) are known to play important roles in mobilities and bio-availabiliities of actinide elements and heavy metals. Most of researches on NOMs have been performed with NOMs isolated from surface environments such as soil and river water. The properties and roles of NOMs in deep groundwater has been largely unknown. In this research we have investigated the physiochemical and ion binding properties of HSs isolated from sedimentary groundwater collected at a borehole at the -150 m experimental stage of the Horonobe underground research laboratory, JAEA. It was the first attempt to clarify details of ion binding to deep groundwater HSs over a wide range of conditions. Horonobe HSs consist of relatively small organic molecules rich in aliphatic C and S, which are rather distinctive, compared with structures and compositions of HSs with surface origins. Although the densities of carboxylic groups, which are supposedly responsible for metal ion binding in HSs, are similar to or even larger than those of surface HSs, the binding of copper ion (Cu2+) is smaller for Horonobe HSs. This can be explained by mono-dentate coordination of the carboxylic groups which are sparsely distributed on aliphatic chains of the HSs. Extended X-ray absorption fine structure analyses have revealed involvement of S in binding of Cu2+ to Horonobe HSs at relatively low pH, […]