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Journal Articles

Chemical species of cesium and iodine in condensed vaporized microparticles formed by melting nuclear fuel components with concrete materials

Onuki, Toshihiko*; Ye, J.*; Kato, Tomoaki; Liu, J.; Takano, Masahide; Kozai, Naofumi; Utsunomiya, Satoshi*

Environmental Science; Processes & Impacts, 25(7), p.1204 - 1212, 2023/07

To elucidate chemical forms of Cs and I in microparticles produced via the Fukushima Daiichi Nuclear Power Plant accident and released into the atmosphere, we analyzed Cs and I in condensed vaporized particles (CVP) produced by melting experiments using nuclear fuel components containing CsI with concrete. CVPs consisted of many round particles containing Cs and I of diameters less than several tens of micrometers. Two kinds of particles were present: one containing large amounts of Cs and I, suggesting the presence of CsI, and the other containing small amounts of Cs and I with large Si contents. Most of CsI from both particles were dissolved in water. On the contrary, some fractions of Cs remained from the latter particles. These results suggest that Cs was incorporated in CVPs along with Si to form water low-soluble CVPs

Journal Articles

Iodate respiration by $$Azoarcus$$ sp. DN11 and its potential use for removal of radioiodine from contaminated aquifers

Sasamura, Seiya*; Onuki, Toshihiko*; Kozai, Naofumi; Amachi, Seigo*

Frontiers in Microbiology (Internet), 14, p.1162788_1 - 1162788_7, 2023/04

 Times Cited Count:0 Percentile:86.15(Microbiology)

$$Azoarcus$$ sp. DN11 previously isolated from gasoline-contaminated groundwater contained a gene cluster involved in bacterial iodate (IO$$_{3}$$$$^{-}$$) respiration. This study determined if strain DN11 performed iodate respiration and assessed its potential use to remove and sequester radioactive iodine ($$^{129}$$I) from subsurface contaminated aquifers. Strain DN11 grew anaerobically with iodate as the sole electron acceptor. After the growth of strain DN11 on iodate, silver-impregnated zeolite was added to the spent medium to remove iodide from the aqueous phase. In the presence of 200 $$mu$$M iodate as the electron acceptor, more than 98% of iodine was successfully removed from the aqueous phase. These results suggest that strain DN11 is potentially helpful for bioaugmentation of $$^{129}$$I-contaminated subsurface aquifers.

Journal Articles

Photocatalytic unification of iodine species using platinum-loaded titanium dioxide

Sugita, Tsuyoshi; Mori, Masanobu*; Kozai, Naofumi

Journal of Photochemistry and Photobiology A; Chemistry, 438, p.114548_1 - 114548_6, 2023/04

 Times Cited Count:0 Percentile:0(Chemistry, Physical)

Removal of iodine from water contaminated by nuclear accidents or the release of radioactive waste is complicated and costly because iodine exists in a variety of forms in the water. We investigated the unification of iodine species by photocatalysis as a pretreatment for removing radioactive iodine species from water. The effect of the TiO$$_{2}$$ crystal phase of Pt-TiO$$_{2}$$ and solution pH on the photocatalytic redox reactions of iodide (I$$^{-}$$), iodate (IO$$_3^{-}$$), and $$o$$-iodobenzoic acid were evaluated. The choice of TiO$$_{2}$$ crystalline phase and pH allowed the mixture of iodine species to be unified to only I$$^{-}$$ or IO$$_3^{-}$$. Regardless of the type of Pt-TiO$$_{2}$$, the iodine in o-iodobenzoic acid was mineralized to I$$^{-}$$ under alkaline conditions. Because the iodine species can be unified to a single species by selecting the photocatalyst and the solution pH, this photocatalytic treatment could be applied to remove iodine species with high efficiency.

Journal Articles

Improvement of the stability of IO$$_{3}$$$$^{-}$$-, SeO$$_{3}$$$$^{2-}$$-, and SeO$$_{4}$$$$^{2-}$$-coprecipitated barite after treatment with phosphate

Tokunaga, Kohei; Tanaka, Kazuya; Takahashi, Yoshio*; Kozai, Naofumi

Environmental Science & Technology, 57(8), p.3166 - 3175, 2023/02

Coprecipitation of radionuclides with barite has been studied to remove radionuclides from radioactive liquid waste because of its excellent removal efficiency; however, little information exists concerning the stability of the ions coprecipitated with barite. This study systematically investigated the stability of iodate, selenite, and selenate coprecipitated with barite via leaching tests. These oxyanions were gradually leached from the oxyanion-bearing barite into ultrapure water over time. Leaching of the oxyanions significantly increased in leaching solutions containing NaCl (pH5.3), NaNO$$_{3}$$ (pH5.9), and Na$$_{2}$$SO$$_{4}$$ (pH5.7). Conversely, leaching of the oxyanions was suppressed in KH$$_{2}$$PO$$_{4}$$ solution (pH8.5), indicating that phosphate stabilized the oxyanion-bearing barite. The effect of phosphate treatment on oxyanion-bearing barite was further investigated. The results showed that the barite surface was modified with phosphate, and a thin surface layer of a barium phosphate-like structure was formed. The amount of oxyanions leached from the phosphate-treated samples into leaching solutions containing NaCl or NaNO$$_{3}$$ was much lower than the amounts leached from the untreated barite samples into ultrapure water. The barite coprecipitation combined with subsequent phosphate treatment may be a promising method to efficiently remove iodate, selenite, and selenate from wastewater and stabilize them as barite coprecipitates.

Journal Articles

Stable C and N isotope abundances in water-extractable organic matter from air-dried soils as potential indices of microbially utilized organic matter

Nagano, Hirohiko*; Atarashi-Andoh, Mariko; Tanaka, Sota*; Yomogida, Takumi; Kozai, Naofumi; Koarashi, Jun

Frontiers in Forests and Global Change (Internet), 6, p.1228053_1 - 1228053_9, 2023/00

Journal Articles

Arsenic and iron speciation and binding in the surface soils in Ningyo-toge mill tailings pond using X-ray absorption fine spectroscopy

Tokunaga, Kohei; Takahashi, Yoshio*; Kozai, Naofumi

Journal of Nuclear and Radiochemical Sciences (Internet), 23, p.14 - 19, 2023/00

Journal Articles

Potential bacterial alteration of nuclear fuel debris; A Preliminary study using simulants in powder and pellet forms

Liu, J.; Dotsuta, Yuma; Sumita, Takehiro; Kitagaki, Toru; Onuki, Toshihiko; Kozai, Naofumi

Journal of Radioanalytical and Nuclear Chemistry, 331(6), p.2785 - 2794, 2022/06

 Times Cited Count:3 Percentile:73.56(Chemistry, Analytical)

Remnant nuclear fuel debris in the damaged nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP) has contacted the groundwater containing microorganisms for over ten years. Herein, we report the possibility of bacterial alteration of fuel debris. We investigated the physical and chemical changes of fuel debris simulants (FDS) in the powder and pellet forms via exposure to two ubiquitous bacteria, Pseudomonas fluorescens and Bacillus subtilis. In the experiments using FDS composed of the powders of Fe(0), solid solution of CeO$$_{2}$$ and ZrO$$_{2}$$, and SiO$$_{2}$$, Ce, Zr, and Si were hardly dissolved, while Fe was dissolved, a fraction of the dissolved Fe was present in the liquid phase as Fe(II) and Fe(III), and the rest was precipitated as the nano-sized particles of iron (hydr)oxides. In the experiment using P. fluorescens and FDS pellet pieces prepared by melting the Fe(0) particles and solid solution of CeO$$_{2}$$ and ZrO$$_{2}$$, the bacteria selectively gathered on the Fe(0) particle surface and made corrosion pits. These results suggest that bacteria in groundwater corrode the iron in fuel debris at FDNPP, change fuel debris into porous one, releasing the nano-sized iron (hydr)oxide particles into the water.

Journal Articles

Chemical species of iodine during sorption by activated carbon; Effects of original chemical species and fulvic acids

Kato, Tomoaki; Kozai, Naofumi; Tanaka, Kazuya; Kaplan, D. I.*; Utsunomiya, Satoshi*; Onuki, Toshihiko

Journal of Nuclear Science and Technology, 59(5), p.580 - 589, 2022/05

 Times Cited Count:3 Percentile:59.77(Nuclear Science & Technology)

This study reports the effect of fulvic acids, which is a natural organic substance generally contained in groundwater, on the oxidation states of radioactive iodine anions (iodide and iodate). Iodide and iodate are contained in the contaminated water of the Fukushima Daiichi Nuclear Power Plant and supposed to be removed by activated carbon (AC) via adsorption. When fulvic acids does not exist in the experimental system, the adsorption of iodide on AC was less than that of iodate and their oxidation states after the adsorption were not changed. When fulvic acids existed, a fraction of the adsorbed iodate was reduced to iodide. This result indicates that the reduction of the adsorbed iodate progresses during the storage of the spent AC.

Journal Articles

Insights into boron removal from water using Mg-Al-LDH; Reaction parameters optimization & 3D-RSM modeling

Eljamal, O.*; Maamoun, I.; Alkhudhayri, S.*; Eljamal, R.*; Falyouna, O.*; Tanaka, Kazuya; Kozai, Naofumi; Sugihara, Yuji*

Journal of Water Process Engineering (Internet), 46, p.102608_1 - 102608_13, 2022/04

 Times Cited Count:13 Percentile:98.61(Engineering, Environmental)

Journal Articles

Sorption of Pu(IV) on biogenic Mn oxide and complexation of Pu(IV) with organic ligands secreted by fungal cells

Tanaka, Kazuya; Tani, Yukinori*; Kozai, Naofumi; Onuki, Toshihiko

Journal of Radioanalytical and Nuclear Chemistry, 331(2), p.1109 - 1114, 2022/02

 Times Cited Count:0 Percentile:0.01(Chemistry, Analytical)

We investigated the sorption of Pu(IV) on biogenic Mn oxide produced by Mn(II)-oxidizing fungus. The sorption of Pu(IV) on biogenic Mn oxide was similar to that of U(VI) and different from that of Th(IV), possibly due to oxidation of Pu(IV) to Pu(VI). When Pu(IV) was sorbed on hyphae only, it was desorbed into the solution phase over time. Pu(IV) could be solubilized by complexation with organic ligands secreted by fungal cells. In particular, Pu(IV) desorption was observed under circumneutral pH conditions.

Journal Articles

Uranium (VI) sorption on illite under varying carbonate concentrations; Batch experiments, modeling, and cryogenic time-resolved laser fluorescence spectroscopy study

Mei, H.; Aoyagi, Noboru; Saito, Takumi*; Kozai, Naofumi; Sugiura, Yuki; Tachi, Yukio

Applied Geochemistry, 136, p.105178_1 - 105178_8, 2022/01

 Times Cited Count:6 Percentile:88.83(Geochemistry & Geophysics)

Journal Articles

Fe, Mn and $$^{238}$$U accumulations in ${it Phragmites australis}$ naturally growing at the mill tailings pond; Iron plaque formation possibly related to root-endophytic bacteria producing siderophores

Nakamoto, Yukihiro*; Doyama, Kohei*; Haruma, Toshikatsu*; Lu, X.*; Tanaka, Kazuya; Kozai, Naofumi; Fukuyama, Kenjin; Fukushima, Shigeru; Ohara, Yoshiyuki; Yamaji, Keiko*

Minerals (Internet), 11(12), p.1337_1 - 1337_17, 2021/12

 Times Cited Count:1 Percentile:12.16(Geochemistry & Geophysics)

Mine drainage is a vital water problem in the mining industry worldwide because of the heavy metal elements and low pH. Rhizofiltration using wetland plants is an appropriate method to remove heavy metals from the water via accumulation in the rhizosphere. ${it Phragmites australis}$ is one of the candidate plants for this method because of metal accumulation, forming iron plaque around the roots. At the study site, which was the mill tailings pond in the Ningyo-toge uranium mine, ${it P. australis}$ has been naturally growing since 1998. The results showed that ${it P. australis}$ accumulated Fe, Mn, and $$^{238}$$U in the nodal roots without/with iron plaque compared with other plant tissues. Among the 837 bacterial colonies isolated from nodal roots, 88.6% showed siderophore production activities. Considering iron plaque formation around ${it P. australis}$ roots, we hypothesized that microbial siderophores might influence iron plaque formation because bacterial siderophores have catechol-like functional groups. The complex of catechol or other phenolics with Fe was precipitated due to the networks between Fe and phenolic derivatives. The experiment using bacterial products of root endophytes, such as ${it Pseudomonas}$ spp. and ${it Rhizobium}$ spp., showed precipitation with Fe ions, and we confirmed that several ${it Ps.}$ spp. and ${it R.}$ spp. produced unidentified phenolic compounds. In conclusion, root-endophytic bacteria such as ${it Pseudomonas}$ spp. and ${it R.}$ spp., isolated from metal-accumulating roots of ${it P. australis}$, might influence iron plaque formation as the metal accumulation site. Iron plaque formation is related to tolerance in ${it P. australis}$, and ${it Ps.}$ spp. and ${it R.}$ spp. might indirectly contribute to tolerance.

Journal Articles

Radiocesium in Shiitake mushroom; Accumulation in living fruit bodies and leaching from dead fruit bodies

Guido-Garcia, F.; Sakamoto, Fuminori; David, K.*; Kozai, Naofumi; Grambow, B.

Chemosphere, 279, p.130511_1 - 130511_10, 2021/09

 Times Cited Count:0 Percentile:6.84(Environmental Sciences)

Cesium (Cs) accumulation by Shiitake was investigated to contribute to the elucidation of radiocesium-cycling mechanisms in forest environments. The results demonstrate that Shiitake non-specifically accumulates Cs while accumulating the essential element K and provide evidence that no selective Cs accumulation (or binding) sites exist within the Shiitake fruit body. Furthermore, the present results show that most accumulated Cs quickly leaches out from the dead fruit body with exposure to water. The leached Cs was largely adsorbable on clay minerals, suggesting that the Shiitake fruit body likely contains Cs in the cation form.

Journal Articles

Effect of bacterial siderophore on cesium dissolution from biotite

Kimura, Tatsuki*; Fukutani, Satoshi*; Ikegami, Maiko*; Sakamoto, Fuminori; Kozai, Naofumi; Grambow, B.*; Yoneda, Minoru*

Chemosphere, 276, p.130121_1 - 130121_7, 2021/08

 Times Cited Count:1 Percentile:6.84(Environmental Sciences)

The adsorption of cesium (Cs) on biotite and dissolution of Cs from Cs-bearing biotite using a siderophore were investigated aiming to contribute to the elucidation of radiocesium migration mechanisms in the soil environment. Cs was adsorbed on a hardly weathered biotite powder sample. A siderophore was extracted and purified from the bacterial culture medium, and the purified siderophore was used in five consecutive dissolution experiments of the biotite samples. The major components of the biotite (Al, Fe, and Mg) were dissolved almost stoichiometrically, strongly suggesting that the siderophore selectively dissolves the broken edges of the biotite. The Cs adsorbed on the broken edges was dissolved rapidly as the siderophore dissolved the broken edges, and then, the Cs adsorbed on the outer planar surface of the biotite particles was slowly dissolved.

Journal Articles

Sewage sludge ash contaminated with radiocesium; Solidification with alkaline-reacted metakaolinite (geopolymer) and Portland cement

Kozai, Naofumi; Sato, Junya; Osugi, Takeshi; Shimoyama, Iwao; Sekine, Yurina; Sakamoto, Fuminori; Onuki, Toshihiko

Journal of Hazardous Materials, 416, p.125965_1 - 125965_9, 2021/08

 Times Cited Count:16 Percentile:86.11(Engineering, Environmental)

Journal Articles

Carbonated nanohydroxyapatite from bone waste and its potential as a super adsorbent for removal of toxic ions

Sekine, Yurina; Nankawa, Takuya; Yamada, Teppei*; Matsumura, Daiju; Nemoto, Yoshihiro*; Takeguchi, Masaki*; Sugita, Tsuyoshi; Shimoyama, Iwao; Kozai, Naofumi; Morooka, Satoshi

Journal of Environmental Chemical Engineering, 9(2), p.105114_1 - 105114_12, 2021/04

 Times Cited Count:7 Percentile:52.52(Engineering, Environmental)

Remediating toxic ion contamination is crucial for protecting human health and the environment. This study aimed to provide a powerful strategy for effectively utilizing bone waste from the food production and preparation industries for removal of toxic ions. Here, we show that immersing pig bone in NaHCO$$_{3}$$ solution produced a carbonated nanohydroxyapatites (C-NHAP). The C-NHAP exhibited high adsorptivity for Sr$$^{2+}$$, Cd$$^{2+}$$, Pb$$^{2+}$$, and Cu$$^{2+}$$. The strontium adsorptivity was about 250 and 4,500 times higher than that of normal bone and synthetic HAP, respectively. The C-NHAP is an eco-friendly, high-performance material that is simple to prepare and should be useful for tackling problems of food waste disposal and environmental pollution.

Journal Articles

Effective removal of iodate by coprecipitation with barite; Behavior and mechanism

Tokunaga, Kohei; Takahashi, Yoshio*; Tanaka, Kazuya; Kozai, Naofumi

Chemosphere, 266, p.129104_1 - 129104_10, 2021/03

 Times Cited Count:5 Percentile:55.48(Environmental Sciences)

Radioactive iodine ($$^{129}$$I) is of great concern owing to its high mobility in the environment and long-term radiotoxicity, but there is a lack of effective techniques for removing iodate (IO$$_{3}$$$$^{-}$$) from aqueous solution. The aim of this study is to develop a new technique for removing radioactive iodate from contaminated solution by using barite (BaSO$$_{4}$$). In the present study, we examined the coprecipitation mechanism of iodate by barite at the molecular level for determining optimum conditions for iodate removal. The results showed that iodate was effectively removed from aqueous solution by coprecipitation, even in the presence of competitive anions in solution. Comparing our method with previous studies, iodate removal efficiency by barite was determined to be about two orders of magnitude greater than that by hydrotalcite-like layered double hydroxide at Cl$$^{-}$$ concentration of 10 mmol L$$^{-1}$$. Extended X-ray absorption fine structure (EXAFS) analysis indicated that incorporated iodate was strongly bound in the crystal lattice of barite by substituting the sulfate site in the structure when the iodine concentration was low. The charge compensation problem from the IO$$_{3}$$$$^{-}$$ substitution in SO$$_{4}$$$$^{2-}$$ site is achieved by the substitution of Na$$^{+}$$-IO$$_{3}$$$$^{-}$$ pairs at the nearest Ba$$^{2+}$$ site. Therefore, considering high removal efficiency and strong binding of iodate in barite, coprecipitation with barite is a promising material for removing radioactive iodate from various aqueous solutions contaminated with iodate.

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

 Times Cited Count:40 Percentile:91.14(Engineering, Environmental)

Journal Articles

Function of microbes on chemical species transformation of radionuclides

Onuki, Toshihiko*; Ozaki, Takuo*; Kozai, Naofumi; Utsunomiya, Satoshi*

Behavior of Radionuclides in the Environment I; Function of Particles in Aquatic System, p.67 - 92, 2020/00

It has been experimentally revealed that microorganisms transform radionuclides. For example, cells of microorganisms such as bacteria and yeast accumulate actinides on the surface. Phosphate ions released from microorganism cells precipitate actinides as phosphates. This chapter discusses the role of environmental microorganisms on migration of actinides in the groundwater around Lake Karachai where a lot of radioactive wastes from nuclear facilities of the Soviet Union.

Journal Articles

Synergy effect of organic acids from plants on mineral dissolution by siderophore-producing bacteria

Kimura, Tatsuki*; Kozai, Naofumi; Sakamoto, Fuminori; Fukutani, Satoshi*; Ikegami, Maiko*

Doboku Gakkai Rombunshu, G (Kankyo) (Internet), 76(7), p.III_375 - III_382, 2020/00

no abstracts in English

242 (Records 1-20 displayed on this page)