Formation of pure NaX zeolite: Effect of ageing and hydrothermal synthesis parameters

Abstract

Among the challenges of synthesizing NaX zeolite is the formation of competing phases during the hydrothermal process which results with impurities in the product. The competing phases of NaX zeolite may include NaP zeolite, hydroxylsodalite and NaA zeolite. In this paper, relationships between the preparation parameters and hydrothermal synthesis parameters towards the formation of high purity of NaX zeolite are studied. The studied parameters include ageing duration, hydrothermal synthesis temperature and hydrothermal synthesis duration. Sodium silicate, sodium aluminate, sodium hydroxide and distilled water are used as the main reactant sources at a fixed molar ratio. The morphology, Si/Al ratio and zeolite phase of the resultant particles were characterized using field emission scanning electron microscope (FESEM), energy-dispersive x-ray spectroscopy (EDS) and X-ray diffraction analyser (XRD), respectively. Hydrothermal synthesis temperature of 90°C and synthesis duration of 16 hours were identified as the optimum synthesis parameters for producing high crystalline, single phase NaX zeolite. In addition, the relationships between synthesis parameters and NaX zeolite produced were also studied. Longer ageing duration and longer hydrothermal synthesis duration results in high crystalline product with potential impurities phases, while higher hydrothermal synthesis temperature produced pure NaX zeolite at shorter hydrothermal synthesis duration.