关键词: NaY zeolite, Submolten salt depolymerized perlite, Alkalinity, Crystallization kinetics

Abstract: NaY zeolites are synthesized using submolten salt depolymerized natural perlite mineral as the main silica and alumina sources in a 0.94 L stirred crystallizer. Effects of alkalinity ranging from 0.38 to 0.55 (n(Na₂O)/n(SiO₂)) on the relative crystallinity, textural properties and crystallization kinetics were investigated. The results show that alkalinity exerts a nonmonotonic influence on the relative crystallinity and textural properties, which exhibit a maximum at the alkalinity of 0.43. The nucleation kinetics are studied by fitting the experimental data of relative crystallinity with the Gualtieri model. It is shown that the nucleation rate constant increases with increasing alkalinity, while the duration period of nucleation decreases with increasing alkalinity. For n(Na₂O)/n(SiO₂) ratios ranging from 0.38 to 0.55, the as-synthesized NaY zeolites exhibit narrower crystal size distributions with the increase in alkalinity. The growth rates determined from the variations of average crystal size with time are 51.09, 157.50, 46.17 and 24.75 nm·h^-1, respectively. It is found that the larger average crystal sizes at the alkalinity of 0.38 and 0.43 are attributed to the dominant role of crystal growth over nucleation. Furthermore, the combined action of prominent crystal growth and the longer duration periods of nucleation at the alkalinity of 0.38 and 0.43 results in broader crystal size distributions. The findings demonstrate that control of the properties of NaY zeolite and the crystallization kinetics can be achieved by conducting the crystallization process in an appropriate range of alkalinity of the reaction mixture.

Key words: NaY zeolite, Submolten salt depolymerized perlite, Alkalinity, Crystallization kinetics