Microwave-ultrasonic Assisted Preparation Of Fly Ash-based NaP Zeolite And Its Adsorption Properties Of Cr(Ⅵ)

With the high-quality development of China’s economy,the dominant position of coal consumption will not fundamentally change at present.However,a large amount of solid waste-Coal fly ash（CFA）will be produced when coal is burned.At present,the application of fly ash in China is mainly used in the construction industry,agriculture,ceramics and other fields,and it is urgent to transform to high value-added utilization.At the same time,with the development of industry,the discharge of chromium-containing wastewater has become increasingly prominent,which has brought great threat and harm to the ecological environment and human health.The preparation and application of high value-added fly ash-based zeolite from coal fly ash for the treatment of heavy metal Cr（Ⅵ）from waste water,which is not only environmental and economic benefits,but also is an effective way to broaden the high value-added resource utilization of coal fly ash.In this thesis,coal fly ash and NaOH was used as raw material,activator,respectively,the molar ratio of silicon to aluminum was controlled by the additional of Al（NO）₃·9H₂O.Coal fly ash-based NaP zeolite was prepared by microwave-ultrasonic-assisted hydrothermal method.The process parameters of preparing fly ash-based NaP zeolite was optimized using BBD response surface methodology.The physicochemical properties of coal fly ash-based NaP zeolite were characterized by XRD,FT-IR,BET,SEM,TEM,UV-Raman and TG-DSC.The effects of alkali-ash ratio,pre-crystallization time,crystallization time and silicon-aluminum ratio on the preparation of fly ash-based NaP zeolite were investigated.The crystallization mechanism of fly ash-based NaP zeolite was discussed,and the crystal growth kinetic parameters of NaP zeolite crystals at different temperature ranges were calculated.The adsorption performance of pure fly ash-based NaP zeolite for aqueous solution of Cr（Ⅵ）was evaluated.The results are as follows:（1）The results of BBD response surface process parameters optimization of fly ash-based NaP zeolite show that coal fly ash-based NaP zeolite with single phase,high purity and good thermal stability can be prepared when the mass ratio of alkali to ash is 1.5,the pre-crystallization time is 2 h,the crystallization time is 48h,and the molar ratio of silicon to aluminum is 5.Coal fly ash-based NaP zeolite with a specific surface area of 48.85 m²/g,an average pore diameter of 5.13 nm,and a relative crystallinity of over 90%.The relationship between the two interaction factors on the preparation of fly ash-based NaP zeolite is as follows:alkali-ash ratio>silicon-aluminum ratio>crystallization time>pre-crystallization time.（2）The influencing factors have great influence on the preparation of coal fly ash-based NaP zeolite.Zeolites with other crystalline phases was formed when mass ratio of alkali to coal fly ash was too high,while insufficient crystallization was occured when mass ratio of alkali to coal fly ash was too low.The proper increased of molar ratio of Si to Al is beneficial to the formation of coal fly ash-based NaP zeolite.Crystallization time has an important influence on the structure of zeolite.Crystal nucleus will grow incompletely if crystallization time is too short,while crystal grains will accumulate if crystallization time is too long.The influence factors are consistent with BBD response surface analysis results.（3）The results of crystallization mechanism of fly ash-based NaP zeolite show that the crystal formation mechanism of fly ash-based NaP zeolite mainly goes through the following steps:formation of initial gel,formation of crystal nucleus,formation of primary structural unit（silicon-oxygen tetrahedron）,formation of secondary structural unit（8 MR,4 MR）and formation of tertiary structural unit（GIS skeleton topology）.（4）The results of kinetic parameters of fly ash-based NaP zeolite at different temperatures indicate that the apparent activation energy E_a=2.08 KJ/mol,the pre-exponential factor A=85.63,the apparent growth rate constant K in the process of crystal growth,and the crystallization reaction order q.The analysis result show that the apparent rate constant K of crystal growth is according with the general law of increasing with the temperature.（5）The results of adsorption of aqueous Cr（Ⅵ）on fly ash-based NaP zeolite show that the adsorption is saturated and the adsorption effect is the best（the adsorption capacity of 7.54 mg/g and the removal rate of 90.48%）when the concentration of Cr（Ⅵ）solution of 50 mg/L,the pH value of 3 and the adsorption time is about 200 min.