Regulation On The Synthesis Process Of Coal Fly Ash-based NaP Zeolite And Its Removal Performance For Metal Ions And Organic Pollutants

Based on the low utilization rate of coal fly ash and the characteristics of metal ions and organic pollutants in the water bodies,a new idea of preparing the zeolite from coal fly ash waste to remove the metal ions and organic pollutants in the wastewater was proposed,i.e.,taking the solid waste coal fly ash as raw material,the silica and aluminum components were extracted through the grading treatment to synthesize the NaP zeolite.The enhancement of mass transfer and other methods were adopted to regulate the crystallization process of NaP zeolite.The adsorption and oxidative degradation of metal ions and organic dyes were conducted by employing the prepared NaP zeolite as the adsorbent to achieve the deep removal of pollutants.Meanwhile,the kinetic and thermodynamic parameters of the adsorption process were calculated to clarify the removal and recycling mechanism of NaP zeolite for pollutants,which provided a theoretical basis for the resource utilization of coal fly ash and the harmless treatment of industrial wastewater.The main findings of this paper were as follows:（1）NaP zeolite was prepared by the conventional static hydrothermal synthesis method,with the optimized crystallization parameters of an ageing temperature of 30℃,an ageing time of 0.5 h,a crystallization temperature of 120℃,a crystallization time of 8 h,n（H₂O）/n（SiO₂）=116,n（Na₂O）/n（SiO₂）=1.4,n（SiO₂）/n（Al₂O₃）=2.8,in which the crystallinity of NaP zeolite was 98.98%and the crystal grain size was～2.78μm.The crystallization kinetics study of NaP zeolite demonstrated that the diffusion mechanism dominated the process.Thus,the enhancement of mass transfer was achieved via the regulation of the reactant concentration,the crystallization mode（dynamic crystallization mode,external ultrasound,or microwave enhancement methods）,and the introduction of external crystalline seeds.When the external ultrasound was employed to enhance the mass transfer（the output power of 360 W）,the induced nucleation period of the crystal was shortened from～2.0 h to～0.5 h,the crystal growth rate was significantly increased,and the crystal grain size was reduced to～1.65μm.（2）The conversion of amorphous aluminosilicate gels and the formation and growth process of the nucleus were regulated by introducing the hindrance effect,which achieved the synthesis of NaP zeolites with small and uniform crystal grain size and good dispersion.The NaP-Cy OH zeolite synthesized with the cyclohexanol（Cy OH）owned complete crystal morphology and the specific surface area of 80.4 m²/g.Taking the metal ion Zn（II）as the target pollutant,the adsorption process for Zn（II）using NaP-Cy OH zeolite followed the pseudo-second order adsorption kinetic and Langmuir isothermal adsorption model.During five regeneration cycles,the removal rate reached above 98%.（3）The NaP zeolites doped with metal heteroatoms（M）were prepared using the organic complexation-assisted hydrothermal synthesis method.At n（M）:n（Al₂O₃）=1:8,Co-NaP（the crystallinity was 92.02%）,Ni-NaP（90.76%）,and Fe-NaP（88.45%）zeolites had poor crystallinity effect,and at n（Ti）:n（Al₂O₃）=1:6,Ti-NaP had higher crystallinity（98.22%）.Meanwhile,the metal heteroatoms in the NaP zeolite mainly existed in two forms:the equilibrium state of the charge and the substituted state of the silicon atoms.Taking Zn（II）as the target pollutant,the BET surface area of Co-NaP zeolite was 120.8 m²/g and the adsorption removal rate of Zn（II）using Co-NaP was 99.50%,and still owned excellent adsorption properties after three adsorption-regeneration cycles.（4）The fumed silica（fumed SiO₂）was employed as the silicon source by regulating the occurrence state of silicon source precursors under an alkaline environment and the oligomeric silicon species were generated.The crystallinity of NaP-fumed SiO₂ zeolite via the static hydrothermal synthesis was 84.65%and the crystal grain size was～3.22μm.By the employment of the dynamic hydrothermal synthesis method,the crystallinity of the product was 98.24%and the crystal grain size was reduced to～1.78μm at the rotating speed of 150r/min.Compared with the zeolite synthesized via the static hydrothermal synthesis method,the crystallinity increased by 16.05%and the grain size decreased by 44.72%.Taking the cationic organic dye rhodamine B as the target contaminant,the adsorption removal rate of rhodamine B reached 98.26%using NaP-fumed SiO₂（dynamic）under the coupling effects of pore structure effect,hydrogen bonding,and electrostatic attraction,which exhibited excellent stability even after the five regeneration recycles.（5）Under the external field ultrasound enhancement method,the in-situ organic complexation method was employed to prepare Cu-NaP_ultra zeolite at n（Cu）:n（Al₂O₃）=1:6with a crystallinity of 94.14%and a crystal grain size of～1.80μm under the reaction conditions of a crystallization temperature of 90℃,a crystallization time of 4 h,n（SiO₂）/n（Al₂O₃）=4.0,a ultrasonic power intensity of 30%,and a power density of 60 m L/W.The cationic organic dyes methylene blue（MB）and methyl violet 6B（MV-6B）were selected as the target contaminants,and the oxidative degradation efficiency of MB and MV-6B by Cu-NaP_ultra zeolite Fenton-like catalyst was 93.22%and 98.71%,respectively.The in-situ degradation of organic dyes was achieved via the adsorption enrichment of organic dyes combined with the catalytic oxidation of metal active sites from Cu-NaP_ultra in the presence of active species·OH.