Japan Geoscience Union Meeting 2014

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Oral

Symbol U (Union) » Union

[U-05_30PM2] Interrelation between Life, Water, Mineral, and Atmosphere

Wed. Apr 30, 2014 4:15 PM - 5:45 PM 419 (4F)

Convener:*Tsubasa Otake(Division of Sustainable Resources Engineering, Faculty of Engineering, Hokkaido University), Yohey Suzuki(Graduate School of Science, The University of Tokyo), Fumito Shiraishi(Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University), Ken Takai(Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology), Yuichiro Ueno(Department of Earth and Planetary Sciences, Tokyo Institute of Technology), Takeshi Naganuma(Graduate School of Biosphere Science), Takeshi Kakegawa(Graduate School of Science, Tohoku University), Tadashi Yokoyama(Department of Earth and Space Science, Graduate School of Science, Osaka University), Kentaro Nakamura(Precambrian Ecosystem Laboratory (PEL), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)), Chair:Yohey Suzuki(Graduate School of Science, The University of Tokyo), Takeshi Naganuma(Graduate School of Biosphere Science)

5:15 PM - 5:30 PM

[U05-P18_PG] Anion adsorption and post-adsorption behavior of metastable calcium carbonate polymorph

3-min talk in an oral session

*Takato YAMAMOTO1, Ritsu KODAMA1, Tsutomu SATO1, Tsubasa OTAKE1 (1.Laboratory of Environmental Geology, Hokkaido University)

In Japanese transuranic (TRU) waste disposal facilities, I-129 is the most important radionuclide that must be considered in long-term safety assessments of the repository. However, the degradation of cement materials used in the repositories can produce high pH pore fluids that can affect to anion transport behavior. Therefore, it is necessary to understand the behavior of anions such as I- in hyperalkaline conditions. Examples of I- behavior in natural hyperalkaline environments, such as in Oman, show that I- is taken up by aragonite, opening up the possibility of calcium carbonates as inhibitors of I- migration. This concept is currently being applied in the development of the Advanced Liquid Processing System (ALPS), which employs carbonate coprecipitation to treat contaminated waters resulting from the Fukushima Daiichi nuclear power plant accident. However, the stability of the carbonate phases precipitated in this system as well as the anion uptake capacities of these phases are poorly understood. In a previous study, (Kasahara, 2012), it was found that monohydrocalcite (MHC), a precursor of aragonite, affects the iodine capacity of aragonite, making it a possibly important material that can control the behavior of anions..The objective of this study therefore, is to investigate the sorption capacity of MHC for anions and its stability. MHC (Mg2+/Ca2+=6; Ca2+/CO32-=1) was synthesized and used for sorption experiments involving F-, Br-, I-, IO3-, SO42+, CrO42-, HAsO42-, and phase transformation experiments. Results show that Kd values of HAsO42- and F- on MHC are high, while IO3-, SO42- are relatively low. On the other hand, Br-, I-, NO3-, CrO42- were not taken up. It is because MHC has high chemical reactivity and high specific surface (4 times large of aragonite, 15 times large of calcite), in addition MHC is most low density of calcium carbonate, so MHC can takes up relatively large amount of anions than other calcium carbonate. And other thing, MHC involves Mg2+ abundantly. This study indicates that Mg2+ form fluoride adsorption site. Results of the transformation experiments show that MHC with no adsorbed anions easily transforms into a stable phase, whereas MHC loaded with increasing amounts of anions transform after longer durations. It is because the driving force for the transformation decreases with the anions content in the solution. In conclusion, MHC can take up fluoride and oxyanions that ionic radii is similar to carbonate but larger than that. In addition, MHC is stabilized as a function of uptake amount of anions.