Crystal Growth Control Of Nano-ZSM-5 Zeolite With Al?OH?₃ As Aluminum Source Derived From Coal Fly Ash

Coal fly ash?CFA?is a solid waste formed in coal combustion and conversion process,causing the land occupation and environmental contamination and health hazard due to the good deal of emission and accumulation of CFA.More than 70 % of CFA are SiO₂ and Al₂O₃ which is similar to the main components of the molecular sieve.So synthesizing zeolite by using CFA as the raw materials not only can improve the resource utilization value and reduce the cost of the zeolites synthesis,but also can decrease the production,according with the strategic needs of circular economy developing.In this paper,taking Al?OH?₃,obtained from CFA,a solid waste,by calcination and activated and purification,as aluminum source,taking tetraethoxysilane?TEOS?as silicon source,using tetrapropylammonium hydroxide?TPAO H?as template agent to synthesize ZSM-5 zeolites through hydro thermal synthesis.The process parameters of hydrothermal systerm?silica-alumina ratio,crystallization temperature,crystallization time,water-silica ratio?of ZSM-5 zeolites were optimized.The influences of organic steric agent on the preparation of ZSM-5 zeolites were investigated.The adsoption of N i²⁺ was performed to test the properties and regeneration of zeolite products and the mechanism was preliminary analyzed.The crystal growth kinetics under different conditions?crystallization temperature,water-silica ratio,organic steric agent?were also studied to established zeolites crystallization growth dynamics model.We regulated ZSM-5 zeolite synthesis from the perspective of macro and micro.The crystal form and morp Hology and characteristics o f the ZSM-5 zeolites were characterized by X-ray diffraction?XRD?,Scanning electron microscopy?SEM?,Fourier transform infrared?FT-IR?,thermogravimetry-differential thermogravimetry?TGA?,N2-adsorption specific surface area measurements?BET?and Particle size distribution?PSD?analysis,respectively.The results of the studies are as follow:?1?Adding activating agent?Na₂SiO₃?,the stable structure glass pHase and mullite of CFA were transformed into nepHeline,which were soluble in acid,after calcination.The chemical activities of CFA were enhanced and conversion efficiency of CFA was improved in a conclusion.After calcination and dipped in HC l solution the aluminum element was extracted successfully from CFA.Pure Al?OH?₃ was obtained after the pH value of solution was regulated and Fe²⁺,Ca²⁺ and Mg²⁺ were removed.The extraction ratio of aluminum was 80.89%.?2?Taking Al?OH?₃,obtained from CFA,as aluminum source,taking TEOS as silicon source,using TPAOH as template agent to synthesize ZSM-5 zeolites through hydrothermal synthesis.The optimal preparation parameters for ZSM-5 zeolite is as following: n?H₂O?: n?SiO₂?: n?TPAOH?: n?Al?OH?₃?=2400:40:12:1,the crystallization temperature is 140 °C,crystal ization time is 6 h.?3?With the addition of organic steric agents,the crystal size of zeolites was regulated and the yield was increased and BET surface area was aggrandized.The ZSM-5 zeolites with PVP addition were better.?4?The kinetics curves of ZSM-5 zeolites crystal growth presented typical “S” form curves.There are four p Hases in crystallization process: induction period,nucleation period,rapid growth period and slow growth period.Temperature is the main factor of dynamics in the process of zeolite crystallization,molecular sieve nucleation period shortens and crystal growth accelerates as temperature increase;H2O/SiO2 molar ratio is crucial to the entire solution's alkalinity,over-top or low H2O/SiO2 molar ratio adverse to zeolite crystallization when n?H2O?: n?SiO2?=60 is appropriate;With the addition of organic steric agents especially PVP expedite zeolites growth and cut down nucleation period and is conductive to the dispersity and crystal form of ZSM-5 zeolites.The nucleation apparent activation energy of ZSM-5 En=24.18 kJ·mol-1and the growth apparent activation energy of ZSM-5 Eg=10.19 kJ·mol-1.?5?With the addition of organic steric agents,the adsorptive property was reinforced as a result.The ZSM-5 zeolites with PVP addition have admirable adsorptive capacity,the highest removal rate of Ni²⁺ was 92.8% at 30 °C at 60 min.Using EDTA-2Na as a renewable auxiliary with a concentration of 0.01 mol·L-1,regenerating for 30 min under 40 °C,the regenerative adsorption capacity of ZSM-5 zeolites was optimal with a re moval rate of 90.9%.It was found that the dynamic adsoption process of N i²⁺ on ZSM-5 zeolite conformed to Lagergren two-order kinetics model,and it was adorabale that the adorption ability was improved with PVP.