Effects of the structure of silica-alumina gel on the hydrothermal synthesis of kaolinite

Shigeo Satokawa, Yasushi Osaki, Soichiro Samejima, Ritsuro Miyawaki, Shinji Tomura, Yasuo Shibasaki, Yoshiyuki Sugahara

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    Abstract

    Kaolinite was hydrothermally synthesized from two kinds of silica-alumina gels to examine the effect of the structure of the starting material. Two kinds of gels were prepared by precipitation at different pH conditions (pH = 9.6 and 4.2) from solutions containing water glass and aluminum sulfate. Na ions in the gels were removed with a resin before the hydrothermal treatment, but a slight amount of sulfate ions was still present in the gels. The nuclear magnetic resonance spectra of the starting gels suggested that the gel prepared at pH 9.6 consists of networks with alternating SiO4- and AlO4-tetrahedra (partially AlO6-octahedra), whereas the gel prepared at pH 4.2 consists of a sheet structure related to allophane. After the hydrothermal treatment at 220°C for 9 days, kaolinite particles with spherical shape were obtained from the former gel, and platy kaolinite was crystallized from the latter one. The difference in morphology of synthetic kaolinite was attributable to the structures of the starting gels, and the pH values in the hydrothermal reactions were not very significant to the morphology.

    Original languageEnglish
    Pages (from-to)288-297
    Number of pages10
    JournalClays and Clay Minerals
    Volume42
    Issue number3
    DOIs
    Publication statusPublished - 1994

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    Keywords

    • Gel structure
    • Hydrothermal synthesis
    • Kaolinite
    • Nuclear magnetic resonance
    • Silica-alumina gel

    ASJC Scopus subject areas

    • Soil Science
    • Earth and Planetary Sciences (miscellaneous)
    • Geochemistry and Petrology
    • Water Science and Technology
    • Earth and Planetary Sciences(all)
    • Environmental Science(all)

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