Abstract:The production of molecular sieves from coal fly ash (CFA) is an effective way to achieve its high value-added utilization. By using high calcium CFA as raw material, pure ZSM-5 molecular sieves were prepared by a variable-temperature hydrothermal crystallization method combining pretreatment techniques such as high temperature roasting, acid leaching purification and alkali fusion activation. The composition, structure, morphology and acid properties of the samples were characterized by XRD, XRF, FTIR, SEM, NH3-TPD, OH-FTIR and N2 adsorption-desorption. The results show that acid leaching purification can remove more than 96% of calcium oxide, and alkali fusion activation transforms the inert mullite crystalline phase into soluble silica-aluminates. The ZSM-5 molecular sieve prepared by two-step hydrothermal crystallization method has high crystallinity, small particle size (800 nm×300 nm×100 nm) and good dispersion, with high specific surface area (319.22 m2/g), high external surface area (48.28 m2/g) and abundant microporous structure (0.16 cm3/g). Compared with HZSM-5 synthesized by one-step hydrothermal method based on chemical reagents, the high-calcium CFA-based HZSM-5 has slightly lower acid strength, lower total and Bronsted acid amounts, and rises percentage of weak acids, which has good potential for applications in fields such as adsorption and catalysis.