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Doi, Reisuke; Uchikoshi, Keiji*
no journal, ,
Solubility experiments of Se were performed from oversaturation direction in the presence of Fe under reducing conditions to determine the solubility-controlling solid phase of Se. Equilibrium and the steady Se concentrations were reached in 
1 month. The Se solid that was detected by XRD analyses of the solid samples from the equilibrated suspensions was only FeSe
. The thermodynamic interpretations of the solubility data and XRD analyses of the solid samples show FeSe to be SSP.
Amano, Yuki; Ise, Kotaro; Ito, Tsuyoshi; Nemoto, Kazuaki; Tachi, Yukio
no journal, ,
We characterized the geochemical and microbial structures of biofilm samples formed with groundwater from boreholes in the subsurface environment at Horonobe area, Japan. The biofilm samples were grown naturally into the sampling tubes made by nylon under in-situ geochemical conditions. The heavy metal sorption capacities of these biofilms were also determined to evaluate the effects of microorganims on radionuclides transport in HLW systems. From the results of heavy metal analyses, it is revealed that high content of elements was accumulated in the biofilms, and each elements was not accumulated in quantity in the same proportion and had different sorption properties. We could find no discernible correlation between those elements accumulated in the biofilms and the composition of groundwaters. It is assumed that these differences depend on the microbial community structure that composed of biofilms. That is to say, it is possible that microorganims that compose the biofilms selectively accumulate heavy metals according to their metabolic activity. Analyses of 16S rDNA utilizing next generation sequencing indicates that the biofilms were dominated by the phylum Nitrospirae, Proteobacteria, and JS1 and SM1 as Candidate phylum. Over 40% of the detected sequences belong to groups of uncultured microorganisms. These results possibly show the similar characteristics of natural biofilms formed on fracture-surfaces in the subsurface environments. Hence, it is necessary to evaluate mechanisms of interaction between heavy metals, microbial community structure and metabolic activities of biofilms.
Ishidera, Takamitsu; Hayashi, Masanori*; Sukegawa, Akihiro*
no journal, ,
In the geological disposal of radioactive waste, montmorillonite, which is the major mineral component of bentonite, possibly forms colloidal particles due to the erosion of compacted bentonite. To evaluate the impact of colloid on radionuclide migration, distribution coefficient of radionuclides on colloidal montmorillonite is a key parameter. The distribution coefficient on colloidal montmorillonite is considered to be derived from the sorption behavior of radionuclides on non-colloidal montmorillonite (montmorillonite sediment). In this study, the sorption site capacity of colloidal montmorillonite was investigated by acid titration to evaluate the difference of sorption site capacity between colloidal montmorillonite and montmorillonite sediment. The experimental results suggested that the sorption site capacity in colloidal montmorillonite generated in low Na concentration was comparable to that of montmorillonite sediment.
Terashima, Motoki; Saito, Takumi; Ishii, Tomoko*; Akagi, Yosuke*; Tachi, Yukio
no journal, ,
no abstracts in English
Iida, Yoshihisa; Yamaguchi, Tetsuji; Tanaka, Tadao; Hemmi, Ko
no journal, ,
The sorption behavior of thorium (Th) onto granitic rock and its major constituent were investigated by batch sorption experiments. Experiments were carried out under variable pH and carbonate concentrations. Distribution coefficients decreased with increased carbonate concentrations and showed the minimal value at pH 9-10. This sorption tendency was likely due to forming the hydroxide-carbonate complexes of Th in the solutions. The order of sorbability for Th was mica, feldspar, quartz = granite. The sorption behaviors of Th onto these minerals were analyzed by the triple-layer surface complexation model with the Visual Minteq computer program. The model calculations assuming the inner-sphere surface complexation of Th were able to explain the experimental results reasonably well. It was shown that the sorption behavior of Th onto granite can be explained primarily by the complexation with the surface sites of feldspar.
Sasaki, Takayuki*; Kokami, Takayuki*; Amamiya, Hiroki; Murakami, Hiroaki; Amano, Yuki; Iwatsuki, Teruki; Mizuno, Takashi; Kobayashi, Taishi*; Kirishima, Akira*
no journal, ,
For thermodynamic analysis of the trace metals in groundwater, concentrations of Th, U, and rare earth elements (REEs) were investigated at Horonobe Underground Research Laboratory. Groundwater was sampled in anaerobic condition directly from a packed section in the boreholes drilled to 140 m and 250 m depth in drift. The colloidal distribution was checked by an on-site batch ultrafiltration unit using 0.2 
m or 10 kDa membranes. As the result, both Th and U concentrations could be estimated by thermodynamic calculations, assuming that the soluble solid phases are restricted to ThO(cr) and UO(cr), respectively. Meanwhile, the concentrations of REEs were also very low, and significant colloidal distribution for lighter REEs was observed. In the thermodynamic analysis where the lanthanide phosphate was assumed to be a solid phase, the experimental plots matched better with the calculated one, even though the changing trend differs from each other.
Onuki, Toshihiko; Kozai, Naofumi; Sakamoto, Fuminori; Yu, Q.; Yamashita, Mitsuo*; Horiike, Takumi*; Utsunomiya, Satoshi*
no journal, ,
We have studied the elimination of Sr from sea water into biogenic calcite. Biogenic calcite were produced at 30
by a maline microbe of TK2d. SEM and TEM analyses showed that needle shaped precipitates containing Ca and Sr was formed when 1.0 mM Sr was added in the solution with TK2d strain. XAFS analysis indicates that coordination environment of Sr in the biotic coprecipitates differs from that in the abiotic one.
Fujiwara, Kenso; Iijima, Kazuki; Terashima, Motoki; Tachi, Yukio
no journal, ,
Due to the accident of the Fukushima Dai-ichi Nuclear Power Plant, radioactive cesium (Cs) was released in a wide range of areas in and around the Fukushima prefecture. Thus, the chemical condition and mechanism governing transport behavior of Cs should be investigated to predict the behavior of Cs in the natural system. In the brackish water region near the river mouth where a cognate ion (Na, K) concentration increases due to the mixture of seawater, two dynamic evolutions influencing Cs behavior are expected. Firstly, the soil has an ion exchange sites, Cs adsorbed onto ion exchange sites of soil particles is likely to be desorbed. Secondly, decreasing of electrostatic repulsion among clay particles causes aggregation of particles leading to deposition with Cs. In this report, Cs desorption and aggregation of particles such as clays was examined using the seawater of the estuary in the coast and the sediments of the riverbed.