Synthesis and kinetic analysis of zeolites based on fly ash

Abstract

ABSTRACT Rational utilization of fly ash, a widely emitted solid waste, was explored by investigating the effects of various factors on the types and properties of zeolites prepared from fly ash. Additionally, the mechanism for adsorption of ammonium nitrogen onto NaP zeolite synthesized via a one-step hydrothermal method was explored. The characterization studies included scanning electron microscopy (SEM), X-ray diffraction (XRD), and adsorption of ammonium nitrogen from wastewater. The effects of the crystallization time, solid‒liquid ratio, alkali concentration, and crystallization temperature on the performance of the fly ash-derived zeolites were systematically investigated. Adsorption isotherms and kinetic models were employed to analyze the adsorption behavior and mechanisms. The results indicated that the optimal conditions for the zeolite synthesis included a 24-hour crystallization time, a solid‒liquid ratio of 1:10, an alkali concentration of 3 mol/L, and a crystallization temperature of 150°C. Under these conditions, the zeolite exhibited intense diffraction peaks, a large surface area, a regular morphology, and an ammonia-nitrogen adsorption rate of 73.01%. An orthogonal test revealed that the alkali concentration had the most significant impact on the zeolite synthesis, with a range value of 14.28. The isothermal adsorption data for ammonia-nitrogen were consistent with the Freundlich model, while the kinetic studies showed that pseudosecond-order kinetics governed the process.