Kinetics of formation of zeolite Na-A [LTA] from natural kaolinites

被引:101
作者
Gualtieri, A
Norby, P
Artioli, G
Hanson, J
机构
[1] UNIV MILAN, DIPARTIMENTO SCI TERRA, I-20133 MILAN, ITALY
[2] BROOKHAVEN NATL LAB, DEPT CHEM, UPTON, NY 11973 USA
关键词
D O I
10.1007/s002690050032
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The kinetics and mechanism of hydrothermal formation of zeolite A from natural kaolinites have been studied using as starting materials two international kaolinite standards (KGa-1 and KGa-2 from Georgia, USA) exhibiting a different degree of stacking disorder. Precursors utilized for the synthesis were prepared by heating the kaolinites at 800 degrees C. Metakaolinite was also prepared from KGa-1 by thermal activation at 600 degrees C. The hydrothermal syntheses were accomplished by heating the samples in NaOH solutions at temperatures between 70 and 110 degrees C. The kinetic experiments were performed by time-resolved synchrotron powder diffraction in isothermal mode using a transmission geometry and an Image Plate detector. The results of the kinetic analysis are interpreted in the light of the structural state of the starting kaolinite, and of the temperature of activation of the precursor material. For kaolinite activated at high temperature the nucleation and crystallization of zeolite A is essentially independent of the defect density of the original kaolinite, and the thermal history of the precursor seems to be the main controlling parameter. The formation process of zeolite A from metakaolinite materials obtained at lower activation temperatures shows significantly faster reaction rates and lower apparent activation energies. This is again interpreted in the light of the short range inhomogeneities present in metakaolinite. As the reaction proceeds metastable zeolite A transforms into hydroxy-sodalite.
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页码:191 / 199
页数:9
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