Influences of crystallization time, batch molar ratios Al2O3/SiO2 and Na2O/SiO2 on particulate properties of sodalite crystals prepared under room-temperature conditions

Abstract

Sodalite crystals were prepared by the hydrothermal method under room-temperature conditions. The influences of crystallization time, batch molar ratios Al2O3/SiO2 and Na2O/SiO2 on the crystalline end products were investigated. For comparison, an experiment was also carried out in which sodalite was synthesized at 90 °C for 10 h. The results revealed that with the prolongation of crystallization time from 1 h to 14 days, the crystallization followed a sequence of phase transformations from an amorphous phase to zeolite NaA, and finally to sodalite. Spherical sodalite crystals composed of very small crystallites were obtained after 10 h of room-temperature crystallization. Whereas, with the same gel composition, the sodalite synthesized at 90 °C for 10 h was large lepispherical particles. High Al2O3/SiO2 molar ratio favored the generation of smaller individual sodalite nanocrystals, which resulted in the formation of larger steady congregated agglomerates. Moreover, alkalinity circumstance determined whether or not sodalite was formed. Well-developed cubic zeolite NaA particles were obtained at Na2O/SiO2 = 1.4; when the Na2O/SiO2 was increased to 8.0, zeolite NaZ-21 crystals were generated, meanwhile, the decomposition of wool ball-like sodalite particles into nanorods was also observed.