Refine your search:     
Report No.
Search Results: Records 1-20 displayed on this page of 345

Presentation/Publication Type

Initialising ...


Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...


Initialising ...


Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

Saccharide-mediated transformation of Ce during the formation of manganese (hydr)oxide

Deng, G.*; Ma, T.*; Tanaka, Kazuya; Onuki, Toshihiko*; Qiu, X.*; Yu, Q.*

Geochimica et Cosmochimica Acta, 286, p.143 - 158, 2020/10

 Times Cited Count:0 Percentile:100(Geochemistry & Geophysics)

In this study, Ce(III) adsorption on Mn(IV) oxide was investigated in the presence of dextran, one of polysaccharides. As a result, Ce(IV) on Mn(IV) oxide was solubilized by the complexation with dextran.

Journal Articles

Spectroscopic and first-principles investigations of iodine species incorporation into ettringite; Implications for iodine migration in cement waste forms

Guo, B.*; Xiong, Y.*; Chen, W.*; Saslow, S. A.*; Kozai, Naofumi; Onuki, Toshihiko*; Dabo, I.*; Sasaki, Keiko*

Journal of Hazardous Materials, 389, p.121880_1 - 121880_11, 2020/05

Journal Articles

Adsorption mechanism of ReO$$_{4}$$$$^{-}$$ on Ni-Zn layered hydroxide salt and its application to removal of ReO$$_{4}$$$$^{-}$$ as a surrogate of TcO$$_{4}$$$$^{-}$$

Tanaka, Kazuya; Kozai, Naofumi; Yamasaki, Shinya*; Onuki, Toshihiko; Kaplan, D. I.*; Grambow, B.

Applied Clay Science, 182, p.105282_1 - 105282_8, 2019/12

 Times Cited Count:1 Percentile:77.56(Chemistry, Physical)

In this study, Ni-Zn layered hydroxide salt (LHS) was used for adsorption experiments of ReO$$_{4}$$$$^{-}$$, as a surrogate of TcO$$_{4}$$$$^{-}$$, in aqueous solutions with various initial Re and sodium salt concentrations. The maximum adsorption amount of Re was estimated at 127.7 mg/g (6.86 $$times$$ 10$$^{-4}$$ eq/g) by fitting adsorption isotherm of ReO$$_{4}$$$$^{-}$$ to Langmuir plot. The adsorption of ReO$$_{4}$$$$^{-}$$ at neutral pH was a reversible process by anion exchange, and decreased with increasing Cl$$^{-}$$, NO$$_{3}$$$$^{-}$$ and SO$$_{4}$$$$^{2-}$$ in solution. EXAFS analysis indicated that ReO$$_{4}$$$$^{-}$$ was adsorbed as an outer-sphere complex on Ni-Zn LHS. The Ni-Zn LHS is a more robust adsorbent for ReO$$_{4}$$$$^{-}$$ than the Mg-Al LDH in terms of solution pH and tolerance to competing anions, and may be an effective alternative to the traditional and more limited method of removing aqueous TcO$$_{4}$$$$^{-}$$ by reductive precipitation.

Journal Articles

Reduction behaviors of permanganate by microbial cells and concomitant accumulation of divalent cations of Mg$$^{2+}$$, Zn$$^{2}$$+, and Co$$^{2+}$$

Kato, Tomoaki*; Yu, Q.*; Tanaka, Kazuya; Kozai, Naofumi; Saito, Takumi*; Onuki, Toshihiko

Journal of Environmental Sciences, 86, p.78 - 86, 2019/12

 Times Cited Count:0 Percentile:100(Environmental Sciences)

This paper investigated the fate of the dissolved permanganate in aqueous solution after contact with bacterial cells and metal accumulation during precipitation of Mn oxides. When Mn(VII) was contacted with bacterial cells, cells were damaged and Mn(VII) was reduced by cells to lower valence and precipitated as Mn oxides (biomass Mn oxides). When Co$$^{2+}$$ ions were present, Co was incorporated into Mn oxides as Co$$^{3+}$$. These results suggest that Mn(VII) can be used to remove metal ions when introduced to wastewater as disinfectant.

Journal Articles

Formation of radioactive cesium microparticles originating from the Fukushima Daiichi Nuclear Power Plant accident; Characteristics and perspectives

Onuki, Toshihiko*; Satou, Yukihiko; Utsunomiya, Satoshi*

Journal of Nuclear Science and Technology, 56(9-10), p.790 - 800, 2019/09

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

Journal Articles

${it In-situ}$ investigation of radioactive Cs mobility around litter zone in contaminated forest using spent mushroom substrata

Onuki, Toshihiko*; Sakamoto, Fuminori; Kozai, Naofumi; Yamasaki, Shinya*; Sasaki, Yoshito; Niizato, Tadafumi

Journal of Nuclear Science and Technology, 56(9-10), p.814 - 821, 2019/09

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

We used the spent mushroom substrata (SMSs) which are a kind of by-product after growing edible mushrooms for the ${it in-situ}$ investigation of radioactive Cs mobility in litter zone in a forest of Fukushima prefecture, Japan. The powder SMS was filled in a plastic net bag of 0.35$$times$$0.55 m, then was placed in a forest for $$sim$$6 months under three kinds of different conditions without treatment (No treatment), covered with wooden box (With box), and with zeolite placed on upper position of ground surface (With zeolite). We determined the ratio of radioactivity (TF) in the SMS to that of the soil and litter beneath the SMS bags. TFs of "No treatment" and of "With zeolite" were determined between $$sim$$0.01 and $$sim$$0.05 for 6 months. On the other hand, TFs of "With box" were lower by one order at 2 and 4 months than those of "No treatment" and of "With zeolite", and nearly the same values as TFs of "No treatment" and "With zeolite" at 6 months. These results clearly indicate that radioactive Cs accumulates in SMS mainly by throughfall. In addition, for a period of several months, fungi contribute to the accumulation of radioactive Cs in the litter zone, even though radioactive Cs was tightly associated with the soil.

Journal Articles

Role of filamentous fungi in migration of radioactive cesium in the Fukushima forest soil environment

Onuki, Toshihiko; Sakamoto, Fuminori; Kozai, Naofumi; Namba, Kenji*; Neda, Hitoshi*; Sasaki, Yoshito; Niizato, Tadafumi; Watanabe, Naoko*; Kozaki, Tamotsu*

Environmental Science; Processes & Impacts, 21(7), p.1164 - 1173, 2019/07

 Times Cited Count:2 Percentile:66.25(Chemistry, Analytical)

The fate of radioactive Cs deposited after the Fukushima nuclear power plant accident and its associated radiological impacts are largely dependent on its mobility from surface soils to forest ecosystems. We measured the accumulation of radioactive Cs in the fruit bodies of wild fungi in the forest at Iidate, Fukushima, Japan. The transfer factors (TFs) of radioactive Cs from soil to the fruit bodies of wild fungi were between 10 $$^{-2}$$to 10$$^{2}$$, a range similar to those reported for the fruit bodies collected in Europe after the Chernobyl accident and in parts of Japan contaminated by nuclear bomb test fallout. Comparison of the TFs of the wild mushroom and that of the fungal hyphae of 704 stock strains grown on agar medium containing nutrients and radioactive Cs showed that the TFs of wild mushroom were lower. TF was less than 0.1 after addition of the minerals zeolite, vermiculite, phlogopite, smectite, or illite of 1% weight to the agar medium. These results indicate that the presence of minerals decrease Cs uptake by fungi grown in the agar medium.

Journal Articles

A Laboratory investigation of microbial degradation of simulant fuel debris by oxidizing microorganisms

Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Kozai, Naofumi; Yamaji, Keiko*; Onuki, Toshihiko

Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 2 Pages, 2019/05

To decommission the Fukushima Daiichi Nuclear Power Plant (FDNPP), it is necessary to estimate the current status of fuel debris and predicate the possible change under various condition. Some microorganisms may enter the plant due to the seawater injection after accident and future defueling activity. In this study, microbial influence on fuel debris under aerobic condition was experimentally investigated. By culturing some bacteria in the presence of simulant fuel debris in liquid medium, the microbial degradation of fuel debris was observed.

Journal Articles

Study on coordination structure of Re adsorbed on Mg-Al layered double hydroxide using X-ray absorption fine structure

Tanaka, Kazuya; Kozai, Naofumi; Onuki, Toshihiko; Grambow, B.

Journal of Porous Materials, 26(2), p.505 - 511, 2019/04

 Times Cited Count:5 Percentile:46.39(Chemistry, Applied)

In this study, we utilized X-ray absorption fine structure spectroscopy to clarify the coordination structure of Re in Mg-Al LDH as a surrogate of Tc. Adsorption experiments of ReO$$_{4}$$$$^{-}$$ on calcined and uncalcined Mg-Al LDHs were conducted in aqueous solutions with different concentrations of NaCl, NaNO$$_{3}$$, and Na$$_{2}$$SO$$_{4}$$. Calcined Mg-Al LDH showed much higher adsorption than uncalcined one. The adsorption of ReO$$_{4}$$$$^{-}$$ was reversible, and decreased with increasing concentration of competing anions like Cl$$^{-}$$, NO$$_{3}$$$$^{-}$$, or SO$$_{4}$$$$^{2-}$$. Analysis of Re L$$_{III}$$-edge extended X-ray absorption fine structure indicated that ReO$$_{4}$$$$^{-}$$ was adsorbed as an outer-sphere complex on Mg-Al LDH. The observed Re adsorption-desorption behavior, which was sensitive to the presence of competing anions, was consistent with the formation of outer sphere-complex.

Journal Articles

Adsorption of Cs onto biogenic birnessite; Effects of layer structure, ionic strength, and competition cations

Yu, Q.*; Tanaka, Kazuya; Kozai, Naofumi; Sakamoto, Fuminori; Tani, Yukinori*; Onuki, Toshihiko

ACS Earth and Space Chemistry (Internet), 2(8), p.797 - 810, 2018/08

Most of Mn oxides are biogenic and known to adsorb cesium (Cs) on the surface. This study investigated structural transformation of biogenic birnessite by accommodating commonly occurring natural heavy metals (Zn, Ni) during the formation of Mn oxides and the influence of those metals on the adsorption behavior of Cs on Mn oxides. It was found that the presence of heavy metals during bio-oxidation of Mn(II), followed by exposure to a low pH aqueous solution, increased the number of available layer vacancies, which consequently increased the adsorption capacity of Cs in the final product birnessite.

Journal Articles

Complexation of Eu(III), Pb(II), and U(VI) with a ${{it Paramecium}}$ glycoprotein; Microbial transformation of heavy elements in the aquatic environment

Kozai, Naofumi; Sakamoto, Fuminori; Tanaka, Kazuya; Onuki, Toshihiko; Sato, Takahiro*; Kamiya, Tomihiro*; Grambow, B.

Chemosphere, 196, p.135 - 144, 2018/04

 Times Cited Count:2 Percentile:90.21(Environmental Sciences)

Transformation of heavy elements by microbes such as bacteria and fungi has been an intense research subject; however, little is known about that of protozoa. This study investigated interaction of a representative protozoa, ${{it Paramecium}}$, with heavy elements (Eu(III), Pb(II), U(VI)). Non-destructive elemental analysis by micro-PIXE hardly detected those elements on living cells after sorption experiments but clearly detected on the cells that were killed with a fixative beforehand. Chromatographic analysis of aquatic species of those heavy elements after the sorption experiments revealed a fraction of those elements bound to a glycoprotein dissolved from the cell surface of living ${{it Paramecium}}$ cells to form soluble pseudocolloid. These findings suggest that complexation of heavy elements with the dissolved surface glycoprotein reduced the sorption of those heavy elements on living cells.

Journal Articles

Preface of SI; RNs in the environments

Tanaka, Kazuya; Kaplan, D. I.*; Onuki, Toshihiko

Applied Geochemistry, 85(Part B), p.119 - 120, 2017/10

 Times Cited Count:0 Percentile:100(Geochemistry & Geophysics)

We have prepared a special issue for Applied Geochemistry entitled "Transformation and Fate of Natural and Anthropogenic Radionuclides in the Environments". Here, we present 13 peer-reviewed articles on the general theme of natural and anthropogenic radionuclides in different environments. At the same time, these articles cover various topics of field research on the distribution of radionuclides, as well as laboratory experiments on adsorption and redox chemistry of these. The articles have been written by the attendees of the session at the Goldschmidt 2016 held in Yokohama, Japan, and by other authors who submitted their manuscripts to Applied Geochemistry focusing on the theme of the special issue.

Journal Articles

Removal of soluble strontium via incorporation into biogenic carbonate minerals by halophilic bacterium Bacillus sp. strain TK2d in a highly saline solution

Horiike, Takumi*; Dotsuta, Yuma*; Nakano, Yuriko*; Ochiai, Asumi*; Utsunomiya, Satoshi*; Onuki, Toshihiko; Yamashita, Mitsuo*

Applied and Environmental Microbiology, 83(20), p.e00855-17_1 - e00855-17_11, 2017/10

 Times Cited Count:8 Percentile:42.33(Biotechnology & Applied Microbiology)

Radioactive strontium ($$^{90}$$Sr) leaked into the ocean from the Fukushima Daiichi Nuclear Power Plant after the nuclear accident. Since the removal of Sr using general adsorbents is not efficient at high salinity, this study investigated removal of soluble Sr from a saline solution by biogenic carbonate minerals. An isolate, Bacillus sp. strain TK2d, from marine sediment removed more than 99 % of Sr in a saline solution. Sr adsorbed at the cell surface and then carbonate minerals containing Sr developed outside the cells.

Journal Articles

Quantitative analysis of radiocesium retention onto birnessite and todorokite

Yu, Q.*; Onuki, Toshihiko*; Kozai, Naofumi; Sakamoto, Fuminori; Tanaka, Kazuya; Sasaki, Keiko*

Chemical Geology, 470, p.141 - 151, 2017/10

 Times Cited Count:5 Percentile:58.98(Geochemistry & Geophysics)

In this work, the Cs retention onto two types of Mn oxide was investigated. We found that Todorokite has sorption sites with a higher selectivity for Cs than birnessite. When the initial Cs concentration was 10$$^{-9}$$ mol/L for the sorption experiments, approximately 34% of the sorbed Cs was residual in the todorokite after the extraction using 1 M NaCl and NH$$_{4}$$Cl; this value was much higher than the results for the Cs-sorbed birnessite. These results strongly suggest that todorokite contributes to the fixation of radioactive Cs in soils.

Journal Articles

Sorption behavior of Np(V) on microbe pure culture and consortia

Onuki, Toshihiko; Kozai, Naofumi; Sakamoto, Fuminori; Utsunomiya, Satoshi*; Kato, Kenji*

Chemistry Letters, 46(5), p.771 - 774, 2017/05

 Times Cited Count:0 Percentile:100(Chemistry, Multidisciplinary)

The sorption behavior of Np(V) by the microbe consortia and by a single pure culture of Fe reducing bacterium was studied at pH between 3 and 7 in resting cell conditions. The sorption of Np(V) by the Fe reducing bacterium obtained in the inert condition and by the consortia in aerated condition were higher than by the Fe reducing bacterium in aerobic condition at pH below 5, strongly suggesting presence of other mechanism than the adsorption on microbial cell surface, i.e. reduction to Np(IV).

Journal Articles

Calcium-deficient hydroxyapatite as a potential sorbent for strontium

Sekine, Yurina; Motokawa, Ryuhei; Kozai, Naofumi; Onuki, Toshihiko; Matsumura, Daiju; Tsuji, Takuya; Kawasaki, Riku*; Akiyoshi, Kazunari*

Scientific Reports (Internet), 7(1), p.2064_1 - 2064_8, 2017/05

 Times Cited Count:12 Percentile:33.7(Multidisciplinary Sciences)

A calcium (Ca)-deficient hydroxyapatite was investigated for its potential to remove Sr$$^{2+}$$ from environmentally relevant water. We conducted sorption tests on solutions having Mg$$^{2+}$$ and Ca$$^{2+}$$ as competing cations at the Sr$$^{2+}$$ concentration of 0.05 mmol/L. The Ca-deficient hydroxyapatite maintained its high Sr$$^{2+}$$ sorption ratio: the sorption ratio was above 80% in the presence of Mg$$^{2+}$$ and Ca$$^{2+}$$ in the concentrations between 0.1 to 1.0 mmol/L, whereas stoichiometric hydroxyapatite showed a lower ratio even in the presence of small amounts of Mg$$^{2+}$$ and Ca$$^{2+}$$. The bonding states of Sr$$^{2+}$$ onto the Ca-deficient hydroxyapatite were evaluated by extended X-ray absorption fine structure measurements. The results indicated that there are specific sorption sites in Ca-deficient hydroxyapatite where Sr$$^{2+}$$ could be stably and preferentially immobilized.

Journal Articles

Effect of flavin compounds on uranium(VI) reduction- kinetic study using electrochemical methods with UV-vis spectroscopy

Yamasaki, Shinya*; Tanaka, Kazuya; Kozai, Naofumi; Onuki, Toshihiko

Applied Geochemistry, 78, p.279 - 286, 2017/03

 Times Cited Count:1 Percentile:90.37(Geochemistry & Geophysics)

This study examined the rate constant for the U(VI) reduction process by three flavin analogues, which are redox-active biomolecules secreted from anaerobic bacteria, to elucidate their substituent group effect on the U(VI) reduction rate by electrochemical methods. The formation of the U(IV) was monitored by UV-vis spectrometry in the presence of the flavins. The rate constant for the U(VI) reduction by the flavins was determined. The apparent reduction potential of U(VI) increased about 0.2 V in the presence of the mediators, which strongly suggests that the biological electron mediator makes the U(VI) reduction possible even under more oxidative conditions.

Journal Articles

Development of paper sludge ash-based geopolymer and application to treatment of hazardous water contaminated with radioisotopes

Li, Z.*; Onuki, Toshihiko; Ikeda, Ko*

Materials, 9(8), p.633_1 - 633_17, 2016/08

 Times Cited Count:15 Percentile:38.11(Chemistry, Physical)

Geopolymer samples were prepared at room temperature using paper sludge ashes and immobilization of Sr and Cs in these samples were evaluated by short-term leaching test. The prepared geopolymer samples were semi-crystalline and porous. For the leaching test, the geopolymer samples containing 1 weight % of strontium nitrate or cesium nitrate were prepared, crushed to be finer than 4 mm in size, and immersed in a phthalic salt buffer (pH4) for 6 h. About 0.2% of Sr and 1.3% of Cs were leached from the geopolymer samples.

Journal Articles

Direct accumulation pathway of radioactive cesium to fruit-bodies of edible mushroom from contaminated wood logs

Onuki, Toshihiko; Aiba, Yukitoshi*; Sakamoto, Fuminori; Kozai, Naofumi; Niizato, Tadafumi; Sasaki, Yoshito

Scientific Reports (Internet), 6, p.29866_1 - 29866_6, 2016/07

 Times Cited Count:4 Percentile:83.31(Multidisciplinary Sciences)

We here first report the direct accumulation pathway of radioactive Cs from contaminated wood logs to the fruit-bodies of shiitake mushrooms through the basal portion of the stipe by using $$gamma$$ spectroscopy, autoradiography, and X-ray micro CT techniques.

Journal Articles

Radioactive Cs in the estuary sediments near Fukushima Daiichi Nuclear Power Plant

Yamasaki, Shinya*; Imoto, Jumpei*; Furuki, Genki*; Ochiai, Asumi*; Onuki, Toshihiko; Sueki, Keisuke*; Namba, Kenji*; Ewing, R. C.*; Utsunomiya, Satoshi*

Science of the Total Environment, 551-552, p.155 - 162, 2016/05

 Times Cited Count:22 Percentile:23.89(Environmental Sciences)

Cesium-137 ($$^{137}$$Cs) of estuary sediment impacted by the FDNPP was measured. Increasing radioactivity was observed from surface to bottom. 90% of the $$^{137}$$Cs was strongly bound to clay minerals in the estuary sediments. These results suggest that $$^{137}$$Cs is being transported from contaminated paddy fields to the estuary.

345 (Records 1-20 displayed on this page)