Construction of fly ash-based NaA/NaX double crystal zeolite and its synergistic adsorption of ammonia nitrogen
The synthesis of zeolite molecular sieves(referred to as GFS)using fly ash as a raw material was carried out in three stages.The method employed for this synthesis was called"combined modification three-step synthe-sis",which involved ultrasonic-assisted alkali fusion microwave crystallization combined with waste glass/13X seed/NaH2PO4 impregnation.To compare the results,traditional alkali fusion hydrothermal synthesis was used to synthe-size zeolite molecular sieves(referred to as FS).In addition,zeolite molecular sieves(referred to as WFS)were syn-thesized using the"three-step synthesis"method of ultrasonic-assisted alkali fusion microwave crystallization.The materials were characterized using various techniques including X-ray diffraction(XRD),scanning electron micros-copy(SEM),Fourier-transform infrared spectroscopy(FTIR),energy-dispersive spectroscopy(EDS),and N2 adsorp-tion-desorption analysis to determine their composition,morphology,and structure.The results indicated that WFS and GFS exhibited higher specific surface areas and well-developed mesopores and micropores compared to FS.Additionally,the crystal type of zeolite molecular sieves shifted from NaA single crystal to NaA/NaX twin crystal.Ammonia nitrogen adsorption experiments revealed that GFS(56.01 mg·g-1)showed better adsorption performance than WFS(49.17 mg·g-1)and FS(39.75 mg·g-1).The adsorption of ammonia nitrogen follows the second-order kinet-ics model and the Langmuir model,as indicated by kinetic and thermodynamic data.This process primarily relies on ion exchange and is both spontaneous and exothermic.Lower temperatures enhance the adsorption of ammonia nitrogen.
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