Synthesis Of Fly Ash-derved Nano-Zeolite Material And Its Application In The Simultaneous Removal Of Ammonium And Phosphate In Wastewater

Fly ash (FA) is one of the largest emissions of solid waste in China, while its effective utilization rate is low and its disposal as landfill poses major challenges and serious economic and environmental problems. However, zeolite synthesis from FA (ZFA) has been receiving a lot of attention and the potential use of ZFAs in water decontamination has been evaluated by a number of research groups. Because the the transformation mechanism of ZFAs from FA is unclear and waste water with high concentrations of nitrogen and phosphorus can not be effectly treated by ZFAs. This paper focuses on the synthesis mechanism of fly ash/nano-zeolite composite material from fly ash and optimization of the synthesis program. Try the doping method and the cation exchange method to modify the synthesized product in order to simultaneous removal of ammonia nitrogen and phosphates in livestock waste water. Conclusions of this study were summarized as follows:Different FAs were collected from four thermal power plans in China (Hangzhou, Beilun, Changxing and Kaifeng). To clarify the mechanism of zeolite synthesis from fly ash, the hydrothermal reaction was carried out. The changes in various physical and chemical properties, such as crystal structure, chemical composition, surface structure of the obtained zeolites and the dissolved amount of Si and Al in alkali solution were investigated during the hydrothermal reaction. The zeolitisation mechanism mainly consists of five successive steps. The first step is the induction period or initial period in the first 0.5h with the fly ash and alkali solution mixed together and the temperature of the slurry reaches to the setted value. The second step is called accelerated phase or dissolution phase in the reaction time of 0.5-12h, the dissolution of the FA leads rapidly to the reprecipitation of a rather Si-rich aluminosilicate gel intermediate. The third stage is the pseudo-equilibrium phase or the nucleation phase in the reaction time of 12-24h with formation of nuclei in aluminosilicate gel. During the fourth stage of the arpid growing or crystalline in the reaction time of 24-48h, the rapid crystallisation of nano zeolite-NaPl begin. The last stage is called stable or transformation phase after 48h with partial transformation of Na-Pl zeolite into the more stable hydroxysodalite or analcime.The optimal conditions for synthesis of fly ash/nano-zeolite composite material composite particles with the hightest cation exchange value (CEC) were with the reaction time of 48h, the liquid to solid ratio of 6ml/g, the NaOH concentration of 2mol/L and the reaction temperature of 95℃.According to comparative analysis of the physical and chemical properties the products synthesized from four different fly ash samples, it was found that the fly ash from Beilun and Changxing with higher Si/Al ratio (Si/Al ratio of 1.82 and 1.52, respectively) were more suitable for synthesis of zeolite materials than that from Hangzhou and Kaifeng with lower Si/Al ratio (Si-Al ratio of 0.54 and 1.21, respectively). Besides, the CEC and the SBET values of the synthetic products from the fly ash of Changxing and Beilun increased by two orders of magnitude and one order of magnitude, respectively, compared to that of their original fly ash.In order to improve the adsorption capacity of P of the synthesized zeolite, doping method and the cation exchange method with CaCl2 and MgCl2were conducted. The results showed that the two methods effectively modified the synthesis products and significantly strengthen their phosphorus sorption property.Considering the simultaneous removal of ammonia and phosphate of, the products with cation exchange of Calcium salt treatment was the most suitable for the treatment of anaerobically digested livestock wastewater. The removal rates of ammonia nitrogen and phosphate reached 41.32%-95.00% and 87.72%-98.59% respectively with the dosage of aboved product of 0.25-8.OOg/100ml.When the dosage of fly ash/nano-zeolite composite products by calcium doping or cation exchange treatment reached 8.OOg/100ml, the concentration of ammonium and phosphate of livestock waste water after treatment decreased from 67.46 mg/L and 31.75mg/L to 1.47mg/L and 0.44mg/L respectively, reached the discharge standard of pollutants for livestock and poultry breeding of Zhejiang province.