Tetracosahedral siliceous particles and process for preparation thereof

摘要

Active analcime having a chemical composition comprising 60 to 95% by weight of SiO2, 0.3 to 20% by weight of Al2O3 and 0.02 to 11% by weight of Na2O based on the three components, an X-ray diffraction pattern inherent to analcime and a moisture adsorption of 5 to 30% by weight as determined under conditions of a relative humidity of 90%, an ambient temperature of 25 DEG C. and a standing time of 24 hours, wherein individual particles have a tetracosahedral or angle-rounded tetracosahedral particulate shape and the primary particle size of 0.1 to 50 mu m as determined according to the electron microscope method. This active analcime is obtained by acid-treating a zeolite by using an acid in an amount of 0.1 to 1.2 molar equivalents per mole of the sum of Al2O3 and Na2O components in the zeolite so that the crystal structure of analcime is left. Amorphous silica which is obtained by an acid treatment of a zeolite and is X-ray diffractometrically substantially amorphous, wherein individual particles have a tetracosahedral or angle-rounded tetracosahedral particulate shape and the primary particle size is 0.1 to 50 mu m as determined according to the electron microscope method. This amorphous silica is obtained by acid-treating a zeolite so that Al2O3 and Na2O components are removed in amounts sufficient to render the zeolite amorphous.