Syntheses of zeolite of the gismondine group

Abstract

The synthetic glasses for the experiments are constituted of three chemical systems, namely, CaO‧Al2O3‧nSiO2 (n=2~8), Na2O‧Al2O3‧nSiO2 (n=2~10) and xCaO‧(1-x)Na2O‧Al2O3‧nSiO2 (x-=-0.25~0.75, n=3~5). Experiments were carried out in autoclaves using the synthetic glasses and alkaline solutions as starting materials, under the conditions of 110 ℃, 150℃, 180℃ and 210℃; at autogeneous pressures; and in durations from 1 day to 60 days. Synthetic products were examined by an X-ray diffractometer, scanning electron microscope and electron microprobe. Experimental results show that gismondine, garronite, gobbinsite and amicite have been synthesized in the xCaO‧(1-x)Na2O‧Al2O3‧nSiO2, (x=0.25~0.75,n=3~5) system; gismondine, garronite and gobbinsite in the CaO‧Al2O3‧nSiO2 (n=2~4) system; and, only gobbinsite in the Na2O‧Al2O3‧nSiO2 (n=4~8) system. The synthetic gismondine and amicite exhibit little variation, but garronite and gobbinstie a greater variation in terms of SiO2/ Al2O3, and Ca/(Ca+Na+K) ratios. SiO2/Al2O3 ratios of the synthesized zeolites are generally close to those of the starting glasses. As to cationic compositions of synthetic zeolites, compositions of liquid media seem more influential than those of glasses during syntheses of gobbinsite and amicite. Contrarily, gismondine is essentially related with the initial compositions of glasses, and garronite seemingly with those of both glasses and liquid media.