Clay Science
Online ISSN : 2186-3555
Print ISSN : 0009-8574
ISSN-L : 0009-8574
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Displaying 1-5 of 5 articles from this issue
Invited Review
  • Yasutaka Watanabe
    2023 Volume 27 Issue 3-4 Pages 25-32
    Published: December 26, 2023
    Released on J-STAGE: December 22, 2023
    JOURNAL FREE ACCESS

    Compacted bentonite can be used as an engineered barrier to inhibit radionuclide migration in radioactive waste disposal. Thermal-hydro-mechanical-chemical coupled phenomena occur inside the engineered barrier and change the engineering properties of compacted bentonite, for example, swelling and permeability, for a long-term. Thus far, the properties of bentonite have been investigated in various academic fields, including clay science and mineralogy. The properties of artificially compacted bentonite have also been investigated, specifically to design engineered barriers. Therefore, previous literature and recent findings on the fundamental behavior of compacted bentonite and its influence on the performance of engineered barriers are overviewed from an engineering perspective. The compaction of powdered bentonite and microstructure of compacted bentonite are first introduced. Second, the swelling characteristics and permeability of compacted bentonite are introduced, and microscopic and macroscopic viewpoints on each research subject are distinguished. Furthermore, the effects of chemical alteration under alkaline conditions on the hydro and mechanical properties of compacted bentonite are introduced as an example of a study on thermal-hydro-mechanical-chemical coupled phenomena. An outlook for the further development of the engineering appreciations of bentonite for radioactive waste disposal is provided.

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Papers
  • Sumio Aisawa, Masatoshi Takahashi, Tooru Abe, Chika Chida, Hidetoshi H ...
    2023 Volume 27 Issue 3-4 Pages 33-39
    Published: December 26, 2023
    Released on J-STAGE: December 22, 2023
    JOURNAL FREE ACCESS

    In this work, the removal of boron (B) in wastewater was investigated by the coprecipitation method using bivalent metal ion as a precipitant. From the preliminary experiments conducted under the fundamental conditions, the removal percentage (coprecipitation degree) of B was found to be quite different depend on the kind of metal ions used, and it became the highest as 95.9% when Ni2+ ion was adopted. Also, the residual B concentration was under the limited value (10 mg/L) of the regulation for wastewater. Then, the optimum conditions in this case were studied in detail and the result was as follows; Initial B concentration=300 mg/L, Ni2+/B molar ratio=12/1, temperature 25°C and pH 9–10. Comparing with the Ni–Al layered double hydroxide prepared under the same condition, this nickel hydroxide precipitate indicated much higher removal ability for B. The precipitate obtained at the optimum condition was mainly the layered nickel hydroxide coordinating borate ion in the interlayer space, which basal spacing being 0.80 nm. Depending on the conditions, several other precipitates such as nickel hydroxide hydrate (3Ni(OH)2·2H2O) and theophrastite (Ni(OH)2) formed highly accompanying borate ion on their surface or inside. In conclusion, new simple method for the B removal by the coprecipitation using Ni2+ ion at higher pH was proposed in this study.

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  • Teruhisa Hongo, Shunki Fukuda
    2023 Volume 27 Issue 3-4 Pages 41-48
    Published: December 26, 2023
    Released on J-STAGE: December 22, 2023
    JOURNAL FREE ACCESS

    The dissolution properties of chrysotile in vivo were investigated to reveal the changes in its morphology and structure. Dissolution experiments with a pseudo-biological fluid (pH 7.4) in the flow system revealed that erosion due to dissolution was greater on the outer surface than on the inner surface, with dissolution occurring preferentially in the brucite octahedral layer. The dissolution of chrysotile in the batch system under acidic conditions exhibited an increase in pH due to the dissolved OH ions; as the pH increased, the rate of dissolution decreased. In the dissolution of chrysotile in the flow system under acidic conditions, the dissolution reaction proceeded faster than in the batch system because of the constant pH. Preferential dissolution of Mg from the chrysotile fibers on the fiber bundle surface was observed. As the dissolution reaction proceeded, the octahedral layers of magnesium hydroxide were destroyed, and resulting in two distinct changes in the morphology of chrysotile. One was in the fibrous form of linked nanoparticles, whereas the other was in the form of sheets.

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  • Reira Kinoshita, Shin’ichi Ishimaru
    2023 Volume 27 Issue 3-4 Pages 49-54
    Published: December 26, 2023
    Released on J-STAGE: December 22, 2023
    JOURNAL FREE ACCESS

    Chromotropism in clay-polymer nanocomposite consisted of synthetic saponite, poly-N-isopropylacrylamide (PNIPAAm), and 3,3′,5,5′-tetramethylbenzidine (TMB) was investigated by diffuse reflectance spectroscopy for dry powder specimens and UV-visible absorption spectroscopy for gel specimens. TMB was introduced in the photopolymerized saponite-PNIPAAm via a commonly used cation exchange method. The nanocomposites showed yellow color attributed to TMB radical in dry state but it turned to green by partial formation of blue charge-transfer complex in contacting to water, methanol, and acetonitrile vapor or liquid. The color change was particularly pronounced for acetonitrile and was evident even in a 10% aqueous solution for hydrogels.

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