Abstract
NaP zeolite particles were prepared through a template-free hydrothermal condition at 100 degrees C. Parameters like Na2O/SiO2 and SiO2/Al2O3 molar ratios, gel aging time and aging temperature were investigated for regulating the crystallization of the final product. The samples at different synthesis stages were characterized with N-2 adsorption at -196 degrees C, field emission scanning electron microscopy (FE-SEM), temperature programmed desorption of ammonia adsorption, X-ray diffraction, thermogravimetric and differential scanning calorimetry analysis and Fourier transform infrared spectroscopy. The experimental results evidenced that a high ordering crystallinity of NaP zeolite was obtained at Na2O/SiO2 and SiO2/Al2O3 molar ratios of 1.10 and 1.40, respectively, and a temperature of 100 degrees C for 4 days of aging. FE-SEM image exhibited polycrystalline aggregates of NaP zeolite with crystallite sizes ranging up to 5.04 mu m with cactus/cabbage like structures. The quantitative analysis of the total number of acid sites was found to increase as Na2O increases. The NaP zeolite sample with a Na2O/SiO2 molar ratio of 1.13 exhibited a large fraction of the acid sites on its external surface, contrary to that synthesized with a relevant ratio of 1.10. The optimized NaP zeolite could be successfully bestowed with excellent sorption properties of Ca(II) in aqueous solution. The kinetic parameters for Ca(II) adsorption were thoroughly investigated.