Hydrothermal synthesis of kaolinite and its formation mechanism
Ryu, Kyoung-Won (Korea Institute of Geoscience and Mineral Resources. Geological and Environmental Research Department)
Jang, Young-Nam (Korea Institute of Geoscience and Mineral Resources. Geological and Environmental Research Department)
Chae, Soo-Chun (Korea Institute of Geoscience and Mineral Resources. Geological and Environmental Research Department)

Date:	2010
Abstract:	In spite of many studies of kaolinite synthesis, questions remain as to the transformation of gel into kaolinite, the kinetics of the reaction, and the influence of solution chemistry. The purpose of the present study was to perform a hydrothermal synthesis in order to understand better the transformation from boehmite to kaolinite. Kaolinite was synthesized from amorphous SiO and Al(OH)·xHO at fixed temperature (250°C) and pressure (30 bar). The initial pH of the solution was 2. The reaction time for the synthesis was varied from 2 to 36 h. The physical properties of synthesized kaolinite were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), nuclear magnetic resonance (NMR) spectroscopy, field-emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersive spectrometry (EDS). The early stage of kaolinite synthesis followed activation of amorphous Al(OH)·xHO to initiate the reactions, i. e. ionization and subsequent crystallization of boehmite. The boehmite reacted continuously with Si dissolved in solution and gradually transformed to disordered, lath-shaped boehmite. In XRD and IR patterns, the typical peaks of boehmite were weakened or disappeared following the reaction. Structural transformation from boehmite to kaolinite occurred when the Al/Si ratio of the aluminosilicate was 1. 0. The kaolinite formed was in the form of curved flakes and its crystallinity increased with reaction time. In the final stage of reaction the morphology of kaolinite changed from flaky to polygonal. The hexagonal, platy kaolinite was therefore developed to allow the gradual variation of the chemical composition, crystal structure, and morphology.
Rights:	Tots els drets reservats.
Language:	Anglès
Document:	Article ; recerca ; Versió publicada
Subject:	Boehmite ; Hexagonal ; Kaolinite ; Synthesis ; Transformation
Published in:	Clays and Clay Minerals, Vol. 58, Núm. 1 (2010) , p. 44-51, ISSN 1552-8367

DOI: 10.1346/CCMN.2010.0580104

8 p, 1.3 MB  UAB restricted access

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