Synthesis and characteristics of Na-A zeolite from natural kaolin in Korea

Abstract

Well-crystallized Na-A zeolite (Z-Kln) was synthesized from natural kaolin using a fusion/hydrothermal method. The crystal morphology and crystallinity of the Z-Kln were characterized with respect to the NaOH/kaolin ratio, SiO2/Al2O3 (Si/Al) molar ratio, and particle size. The relative crystallinity of the Z-Kln from 64.36 to 83.98% increases when NaOH/kaolin ratio increased from 0.6 to 0.9, however, no longer increases at the NaOH/kaolin ratio of 1.2. TEM images of the Z-Kln at the NaOH/kaolin ratio of 0.9 clearly showed the morphology of nanocrystals inside the hybrid silica matrix with the presence of Na, Al, O, and Si. The sizes of the Z-Kln crystals tended to decrease with increasing NaOH/kaolin ratios from 0.6 to 1.2. Tiny crystals of ~1.67 μm or less formed at a NaOH/kaolin ratio of 1.2. For obtaining high crystallinity, the fusion/hydrothermal method is proven to be effective to synthesize the Z-Kln at low alkali condition from the natural kaolin. Hence, this method will be a potential tool for producing cost-effective commercial products from natural materials using simple chemical processes.