Optimize Synthesis Of Zeolite From Fly Ash And Its Application In The Simultaneous Remoyal Of Ammonium And Phosphate In Wastewater

According to the research results of treatment for the second tank’s effluent from Sibao and Qige sewage treatment plant by using zeolite synthesized form fly ash (ZFA) by conventional method, the effect is not very ideal due to its low ammonium and phosphate concentration. So the synthesis process should be improved to perfect its adsorption properties. Because of the insufficient of active Si and Al content and metal oxide compositions affecting the formation of zeolite in fly ash (FA), it is not enough that using the simple, conventional method of zeolite synthesized from fly ash. From three aspects in this paper, the acid pretreatment, adding diatomite or metakaolin and Al modification, we hope to optimize the capacity of simultaneous removal of ammonium and phosphate by ZFA, so as to enhance the added value of ZFA, especially to provide a potential adsorption material for wastewater of low ammonium and phosphate concentrations (the second pond effluent of municipal wastewater, the eutrophication of water body pollution) treatment.The raw materials were collected from four thermal power plants in China (Hangzhou, Beilun, Changxing and Kaifeng) in this study. And based on previous studies of the optimal synthesis conditions of ZFA, conclusions of this study were summarized as follows:After acid pretreatment of the four kinds of fly ash, Fe oxides influencing zeolite formation was significantly reduced, then more zeolite Na-P1formation from FA3and FA4, which has moderate Si/Al ratio. Also, acid pretreatment made the raw fly ash become rough and form holes, and zeolite crystals chaotically adhered to the irregular surface of fly ash particles after acid pretreatment. Simulating treating wastewater of low ammonium and phosphate concentrations, ammonium removal efficiency by Z-PFA1, Z-PFA3and Z-PFA4multiplied and reached to79.61%-91.19%, much higher than18.02%-43.94%for ZFA1, ZFA3and ZFA4. Phosphate removal efficiency of Z-PFA2and Z-PFA4is significantly higher than that of ZFA2and ZFA4, but it is in vain for improving phosphate removal capacity of ZFA1and ZFA3. Acid pretreatment is a appropriate technology for improving the capacity of simultaneous removal of ammonium and phosphate by zeolite synthesized from fly ash with high Fe2O3content (such as FA4:Fe2O3content21.1%).After adding diatomite into fly ash, it can make full use of Al composition in fly ash, but the utilization of Si is still limited, also it is beneficial to zeolite Na-P1formation. However, adding excess diatomite is useless for the promotion. N removal efficiency of products after adding diatomite to low ammonium concentration wastewater increased significantly, the N removal efficiency were all over50%, even high as80%. But it didn’t work to P removal efficiency as N, even generate negative effects (e.g., FA1). Considering simultaneous removal of ammonium and phosphate promotion of the products, it is more appropriate that adding diatomite to Si/Al of2.5in FA2, FA3, FA4, except FA1(Si/Al=0.54), which is too low Si/Al ratio.After adding different parameter of metakaolin into FA2, FA3, FA4, the peak intensity of zeolite Na-P1in the products enhanced, only for FA1, metakaolin parameter needed to be more than20%. The zeolite particles arranged desultorily on the surface of fly ash particles. Adding metakaolin in zeolite synthesis reaction of fly ash can significantly improve N removal capacity of the products, and the N adsorption capacity per unit mass of product were increased by1-2times, but P removal capacity wasn’t improved too much. Except the products of FA2, to the higher P concentration wastewater (≥2mg/L), P removal capacity was significantly improved. Adding metakaolin is not fit for all kinds of fly ashes to promote simultaneous removal of ammonium and phosphate of the products, but it is appropriate that adding5%parameter of metakaolin into FA2(Si/Al=1.82), which has higher Si/Al ratio.Using Al salt solution (0.5mol/L) to modify ZFAs, N removal efficiency of the products was increased several times over, at the same time, P removal efficiency of the modified products has been improved close to99%(PO43-:0～12mg/L). Al modification is an appropriate method to improve simultaneous removal of ammonium and phosphate of ZFA2, ZFA3and ZFA4, but inappropriate for ZFA1.