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Abe, Takeyasu; Iida, Yoshihisa; Sasamoto, Hiroshi; Ishii, Eiichi
Proceedings of Water-Rock Interaction (WRI-17)/ Applied Isotope Geochemistry (AIG-14), 6 Pages, 2023/08
Cation exchange is one of important elementary reactions among water-rock interactions in sedimentary rocks. In order to model non-constant Na-K-Ca-Mg-H exchange selectivity of sedimentary rocks, exchange isotherms and pH dependence on cation exchange capacity of smectite were analyzed following active fraction model. As the result of comparison of exchangeable cationic composition between measured and calculated, selectivity coefficients determined in this study were preferred to those presented by previous studies. Using the coefficients and groundwater hydrochemistry reported previously, expected compositions of exchangeable cations were calculated. The results suggested that pH and total Na-K-Ca-Mg-H concentration of groundwater are important factors to interpret observed compositional variation in exchangeable base cations.
Miyakawa, Kazuya; Kashiwaya, Koki*; Komura, Yuto*; Nakata, Kotaro*
Geochemical Journal, 57(5), p.155 - 175, 2023/00
Times Cited Count：1 Percentile：23.01(Geochemistry & Geophysics)In the thick marine sediments, groundwater altered from seawater during the burial diagenesis may exist. Such altered ancient seawater will be called fossil seawater. In such a field, groundwater flow is considered extremely slow because it is not affected by the seepage of meteoric water even after the uplift. During diagenesis, dehydration from silicates causes changes such as a decrease in the salinity of the porewater. However, dehydration reactions alone cannot quantitatively explain water chemistry changes. In this study, we developed an analytical model that considers the dehydration reaction from silicates during the burial process and the upward migration of porewater due to compaction and examined the possible evolution of porewater chemistry. The results showed that the water chemistry, which was strongly influenced by the dehydration reaction from opal-A to quartz and from smectite, was similar to the observations from boring surveys. The results suggest that the fossil seawater formed during the diagenesis may have been preserved since the uplift and strongly supports the slow groundwater flow in the area where the fossil seawater exists.
Inagaki, Yaohiro*; Idemitsu, Kazuya*; Arima, Tatsumi*; Maeda, Toshikatsu; Ogawa, Hiromichi; Itonaga, Fumio
Materials Research Society Symposium Proceedings, Vol.713, p.589 - 596, 2002/00
A large number of studies on HLW glass corrosion have shown that the glass reacts with water to form more stable mineral phases (alteration phases) during the long-term geological disposal. The phase formation is essential to evaluate the radionuclide release from the glass during the long-term disposal. The purpose of this study is to evaluate, experimentally, the mineral phase formation from HLW glass and the associated cesium release. Static corrosion tests were performed on powdered R7T7 glass in alkalline solutions at elevated temperatures to accelerate the reaction, and mineral phases formed were analyzed by XRD. The results showed that analcime (zeolite) is formed as the dominant phase coexisting with SiO
(am), and beidellite(smectite) or gibbsite coexists dependiting on the conditions. The solution analysis indicated that most of the cesium is retained in the phases of beidellite and analcime by sorption.
Kozai, Naofumi; Onuki, Toshihiko; Muraoka, Susumu
Materials Research Society Symposium Proceedings, Vol.353, 0, p.1021 - 1028, 1995/00
no abstracts in English
-montmorilloniteKawakita, Ryohei*; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Oda, Chie; Mihara, Morihiro; Sato, Tsutomu*
no journal, ,
no abstracts in English
Kikuchi, Ryosuke*; Fujimura, Tatsuya*; Sato, Tsutomu*; Otake, Tsubasa*; Otomo, Yoko*; Goto, Takahiro*; Suzuki, Satoru*; Taniguchi, Naoki; Suzuki, Hiroyuki*
no journal, ,
Yamada, Hirohisa*; Yokoyama, Shingo*; Watanabe, Yujiro*; Morimoto, Kazuya*; Suzuki, Shinichi; Yaita, Tsuyoshi; Hatta, Tamao*
no journal, ,
Saito, Akito*; Kawakita, Ryohei*; Sakuma, Hiroshi*; Oda, Chie; Honda, Akira; Sato, Tsutomu*
no journal, ,
To understand the swelling behavior of NH
-montmorillonite (MMT), the expandability of monoionic Na-, K- and NH-MMT was investigated by XRD under controlled relative humidity (RH) conditions and molecular dynamics (MD) calculations. XRD results indicate that the expansion properties of NH-MMT are similar to that of K-MMT for RH 
30%. At RH 
30%, however, NH-MMT expands further and has a larger basal spacing than both Na- and K-MMT. MD calculation results showed that NH-MMT reaches a one-layer hydration state under lower RH conditions than that of Na- and K-MMT, and was entirely consistent with the above observations by XRD. It was also confirmed that an irregular motion of interlayer NH
could result from bonds between H atoms of the NH ion and the base O atoms of MMT. This irregular motion enabled the basal spacing of NH-MMT to increase and consequently, to expand further under low RH conditions.
Kawakita, Ryohei*; Saito, Akito*; Sakuma, Hiroshi*; Anraku, Sohtaro; Oda, Chie; Mihara, Morihiro; Sato, Tsutomu*
no journal, ,
no abstracts in English
