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Oral presentation

Molecular geochemistry of interactions of various hard cations and phyllosilicates related to their environmental behaviors and isotope fractionation

Takahashi, Yoshio*; Tsuboi, Hiroyuki*; Yamaguchi, Akiko

no journal, , 

no abstracts in English

Oral presentation

Thermodynamic properties of SiO$$_{2(aq)}$$, HSiO$$_{3}$$$$^{-}$$ and SiO$$_{3}$$$$^{2-}$$

Walker, C.*; Anraku, Sohtaro; Oda, Chie; Mitsui, Seiichiro; Mihara, Morihiro

no journal, , 

Equilibrium constants (${it K}$) describing the formation reactions of SiO$$_{2(aq)}$$, HSiO$$_{3}$$$$^{-}$$ and SiO$$_{3}$$$$^{2-}$$ can be used to derive their thermodynamic properties. However, SiO$$_{2(aq)}$$ was derived from inaccurate quartz solubility data, HSiO$$_{3}$$$$^{-}$$ was not extrapolated to zero ionic strength and SiO$$_{3}$$$$^{2-}$$ is routinely ignored because of its restricted dominance to very high pH $$>$$ 13 solutions. Using quartz and water data as well known "anchor" points, ${it K}$ values describing the formation reactions of SiO$$_{2(aq)}$$, HSiO$$_{3}$$$$^{-}$$ and SiO$$_{3}$$$$^{2-}$$ were revised to derive new thermodynamic properties and revised Helgeson-Kirkham-Flowers equation of state (r-H-K-F EoS) parameters. These properties and parameters can be used in the derivation of the thermodynamic properties of other Si bearing aqueous species/complexes and the thermodynamic properties of cementitious, clay, zeolite, and rock forming minerals, and in calculating groundwater compositions relevant to the geological disposal of radioactive wastes.

Oral presentation

Distribution coefficients of rare earth elements to microorganisms including uncultivated species in deep sedimentary groundwater

Terashima, Motoki; Beppu, Hikari*; Endo, Takashi*; Nemoto, Kazuaki*; Amano, Yuki

no journal, , 

no abstracts in English

Oral presentation

Se(-II) immobilization in Fe(II)-(hydro)oxides; Coprecipitation and post-transformation behavior

Francisco, P. C. M.; Ishidera, Takamitsu; Tachi, Yukio

no journal, , 

Oral presentation

Synthesis of U and Pb-doped calcite; A Novel reference material for in situ U-Pb dating of carbonate

Miyajima, Yusuke*; Saito, Ayaka*; Kagi, Hiroyuki*; Yokoyama, Tatsunori; Hirata, Takafumi*; Roberts, N. M. W.*; Horstwood, M.*

no journal, , 

Direct age determination of carbonate minerals provides valuable insight to paleoenvironmental change, tectonics, and sub-surface fluid-flow. The U-Pb method using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a key technique to date natural carbonates such as fault-hosted calcite that cannot be dated by biostratigraphy or Sr isotope stratigraphy. A natural calcite cement WC-1 (254.4 $$pm$$ 6.4 Ma) is suitable as a reference material to correct elemental fractionation with LA-ICP-MS. However, the resulting uncertainty on a sample date is limited by the heterogeneity of U and Pb distribution in the reference material. Our objective is to synthesize calcite with homogeneous U and Pb concentrations and isotope ratios to be used as novel reference materials. To achieve this, we incorporate incompatible U and Pb into calcite through heat-induced crystallization from amorphous calcium carbonate precipitated from U, Pb-doped reagent solution. LA-ICP-MS analyses of results so far revealed that the U/Ca and Pb/Ca ratios in the synthetic calcites were generally homogeneous with relative standard deviation (2SD, n = 10) better than 4% and 7%, respectively. The Pb/Ca homogeneity of calcites doped with $$<$$1 $$mu$$g/g Pb was up to ~25%. The $$^{207}$$Pb/$$^{206}$$Pb ratio of the synthetic calcites was very homogeneous with $$<$$ 1% variation, whereas the $$^{238}$$U/$$^{206}$$Pb ratio was less homogeneous (2%$$sim$$7% variation). To evaluate the suitability of the synthetic calcite as a reference material, we measured the age of WC-1 using the synthetic calcite for elemental fractionation correction; we could date WC-1 with a precision and accuracy of ~3% (246.6 $$pm$$ 7.3 Ma). This method is a promising alternative in addition to characterising natural carbonate materials for elemental and isotopic composition.

Oral presentation

Effective removal of oxyanions from aqueous solution by coprecipitation with barite

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

no journal, , 

no abstracts in English

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