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Iwatsuki, Teruki; Sasaki, Yoshito; Ito, Tsuyoshi; Asano, Takahiro; Amano, Yuki; Yoshikawa, Hideki; Nakamura, Takamichi*; Nagaoka, Toru*
no journal, ,
Microbial activities and the reaction processes with groundwater and rock minerals up to 500 m below ground level were studied to infer the redox process and buffer capacity of rock materials for the articifitial disturbance such as facility construction at subsurface. Based on results of observation at in-situ and batch experiments, the geochemical modelling using PHREEQC-2 was carried out to develop the numerical simulation techniques on water-rock-microbe interaction system.
Tanaka, Kazuya; Suzuki, Yoshinori*; Onuki, Toshihiko
no journal, ,
Biogenic Mn oxide has attracted many geochemists and microbiologist in terms of the ability to highly adsorb and oxidize various trace elements. Cobalt 60 is one of the important radionuclides released from radioactive wastes. In this study, therefore, we studied Co oxidation by Mn oxide produced by a Mn-oxidizing bacterium. Sorption experiments of Co on biogenic Mn oxides were made in 10 mM NaCl solution containing 20 uM Co at pH3 and 6. Cobalt K-edge (7.709 keV) XANES spectra indicated Co(II) oxidation to Co(III) by the biogenic Mn oxides at pH3 and 6. Trivalent Co is highly insoluble relative to Co(II). Consequently, Co oxidation strongly affects the behavior of Co in natural environments. In particular, Co oxidation by biogenic Mn oxide contributes to retardation of migration of radioactive Co (i.e 
Co).
with yeast cells sorbing Eu 
Kozai, Naofumi; Onuki, Toshihiko; Koka, Masashi; Sato, Takahiro; Kamiya, Tomihiro; Esaka, Fumitaka
no journal, ,
To reveal the role of protozoa in migration of radionuclides in the environment, this study investigated behavior of Eu during culture of () in media containing yeast on which Eu was sorbed. After the contact of yeast cells with a Eu(III) solution, many nano particles of Eu phosphate formed on yeast cells. cells were cultured with those yeast cells in an inorganic salt solution containing no phosphate. During the culture, the amount of the Eu leached into the aqueous phase was less than 0.1% of the Eu on the yeast cells. As culture time advances, membranous precipitates formed. These membranous precipitates contained undigested and digested yeast cells and dense membranous organic substance filling gaps between those cells. At the end of the culture, many nano particles of Eu phosphate were observed on digested residue of yeast cells. These results suggest that do not impair actinide-retardation action of microorganisms.
Onuki, Toshihiko
no journal, ,
For the estimation of Long-term migration of actinides, retardation of the migration is assumed to be caused by the adsorption of actinides on microorganisms and minerals. JAEA has conducted the research on the mineralization and fixation of actinides after the adsorption by microorganisms and minerals. I show the importance of the post adsorption phenomena that obtained by the study of U mineralization after the adsorption at Koongarra ore deposit, Australia, and by the study of U mineralization on the cell surface of microorganisms.
Onuki, Toshihiko; Jiang, M.; Kamiishi, Eigo*; Utsunomiya, Satoshi*; Tanaka, Kazuya; Kozai, Naofumi; Suzuki, Yoshinori*
no journal, ,
We have investigated the association of heavy REE of Yb with yeast 
after exposure at pH of 3, 4 or 5. A variety of analytical techniques including FESEM-EDS, TEM, ICP-AES, XAFS have been employed to investigate the sequestration mechanism of Yb by yeast as a function of exposure time. Ytterbium concentrations in solutions decrease as the exposure time increases. FESEM, TEM, and XAFS analyses revealed that nano-sized blocky Yb phosphate with amorphous phase formed on the yeast cells surface after 24 h. These results suggest that the sorbed Yb on the cell surfaces reacted with P released from inside of the yeast cell, resulting in the formation of amorphous Yb phosphate.