Synthesis Of 4A Zeolite From Fly Ash Byproducts And Its Adsorption Of Ammonia-nitrogen Wastewater

The widespread existence of ammonia-nitrogen pollutants seriously threatens the health of the water environment.The use of ion-exchange methods to utilize the high-efficiency adsorption performance of zeolite to remove ammonia-nitrogen is an effective method.The cost of traditional synthetic zeolite method is high.The use of fly ash as a raw material can reduce costs,butthepretreatmentprocessofsyntheticzeolitewithflyash directly is more complex and less efficient.In view of the above problems,this paper proposes to synthesize 4A zeolite from the fly ash to extract aluminum intermediates without pretreatment and with high purity of raw materials.The main work is as follows:（1）A method for synthesizing 4A zeolite from aluminum products with fly ash was proposed and characterized.XRD showed that 4A zeolite was the main product,Si O₂ was the main component of 4A zeolite;SEM showed that the4A zeolite had cubic crystal structure and the surface was staggered with two spherical crystal structures;FTIR showed that the absorption band was adsorbed on the surface of 4A zeolite.The vibrations of-OH,internal silicon（aluminum）tetrahedral Si-O and Al-O groups,and the double-ring vibration peak indicated that the 4A zeolite crystal framework was formed.The chemical composition analysis showed that the main composition of 4A zeolite were Al₂O₃ and Si O₂;TG analysis showed that the 4A zeolite had good thermal stability.The pore size analysis showed that the average pore width of 4A zeolite was 0.51 nm;the cation exchange capacity was 405 mmol/100 g,indicating that 4A zeolite had good ion exchange performance.（2）The adsorption performance of 4A zeolite on simulated wastewater of ammonia-nitrogen was studied.The effects of adsorption time,pH,zeolite dosage,initial concentration of ammonia-nitrogen,and coexisting cations on the adsorption performance were investigated.The adsorption performance and mechanism were investigated by using the quasi second order dynamic equation and adsorption isotherm.The results showed that 4A zeolite with a concentration of 5 g·L^-11 was added in ammonia solution with a concentration of 50 mg·L^-1,pH was 6⁹,adsorption for 80 min,the removal rate reached 71.34%.As the initial concentration of ammonia increased,the removal rate decreased and the adsorption capacity increased.Coexisting cations of Na⁺,K⁺,Ca²⁺had strong competition for NH₄⁺,and Mg²⁺had no obvious competition.The experimental data fitting results accorded with the pseudo-second-order kinetic equations and Freundlich model.Langmuir model showed the maximum adsorption capacity was20 mg·g^-1.（3）The adsorption performance of 4A zeolite on the actual wastewater of ammonia-nitrogen was studied.The effects of p H and zeolite dosage on the adsorption performance were investigated,and the best adsorption conditions were determined after comparing with the simulated adsorption results.The results showed that 4A zeolite with a concentration of 8 g·L^-11 was added in ammonia-nitrogen wastewater with a concentration of 50 mg·L^-1,pH was 6⁸,the removal rate can achieve 63.24%.The experimental results can be effectively applied to the treatment of actual ammonia-nitrogen wastewater.（4）A method for advanced treatment of ammonia-nitrogen wastewater by combining 4A zeolite with polyferric sulfate was proposed.The aim was to raise the ammonia-nitrogen discharge standard from Level 1A of Discharge standard of pollutants for municipal wastewater treatmentplant to Grade IV of the Environmental Quality Standard for Surface Water.The order of addition,reaction time,p H,coagulant and 4A zeolite dosage were studied.SEM and XRD methods were used to characterize the adsorption of 4A zeolite-polymeric ferric sulfate.The mechanism of enhanced coagulation by zeolite was described.The results showed that pH was between 5 and 8,and 4A zeolite with a concentration1.0 g·L^-11 was rapidly stirred for 2 min,then polyferric sulfate with a concentration 60 mg·L^-11 was added,followed by rapid stirring for 2 min and slow stirring for 15 min,finally,static sedimentation for 20 min,the treatment effect was the best,and the ammonia-nitrogen concentration can be reduced from5 mg·L^-11 to 1.5 mg·L^-11 or less.Fulfilling the discharge requirements of Class IV water bodies in the Environmental Quality Standards for Surface Water.The main mechanism was the adsorption/flocculation coprecipitation.