Formation Process of Kaolinite under Hydrothermal Condition.

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  • AKIYAMA Yoko
    Department of Applied Chemistry, Faculty of Engineering, Okayama University
  • TAKEDA Shin-ichi
    Department of Applied Chemistry, Faculty of Engineering, Okayama University
  • TARI Isao
    Department of Applied Chemistry, Faculty of Engineering, Okayama University

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  • 水熱条件におけるカオリナイトの生成過程
  • スイネツ ジョウケン ニ オケル カオリナイト ノ セイセイ カテイ

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Abstract

Formation process of kaolinite from silica and Al (NO3)3 as starting materials in acid solution at 230°C was investigated by XRD, MAS-NMR, FT-IR and ICP. The process was found to consist of two phases, the formation of intermediate phase material, and the crystallization phase. In the former, the structure of intermediate material was different from that of silica and kaolinite while in the latter, kaolinite was formed after 62h of reaction time. In order to elucidate the mechanism of formation of the intermediate phase material which resulted from hydrothermal treatment of the starting materials at 230°C in acid solution, the laboratory process also includes determination of the amount of dissolved silica and some detailed observations of silica surface after hydrothermal treatment in Al(NO3)3 solution (pH=3) using SEM. Obtained data showed that the amount of dissolved silica in Al(NO3)3 solution was four times higher than that in solution without Al(NO3)3. Change in the surface morphology of silica was found, and this was caused by the precipitation of boehmite onto the silica surface during the hydrothermal process. It can be concluded that the formation of intermediate material was proceeded by the reaction between dissolved or decomposed chemical species resulting from silica gel surface where boehmite was precipitated and induced the structural change.

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