| As the inevitable soild waste produced from coal-fired power plants,fly ash has become one of the major industrial soild wastes in China.Fly ash has the potential to be an excellent absorbent because of its specific physical structure.Recently,the demand for technology of denitrification and dephosphorization in low concentration wastewater increased as the increase in discharging of wastewater containing nitrogen and phosphorus.Jianlong steel wastewater(low concentration of nitrogen and phosphorus after vanadium precipitation)was used in this thesis and the fly ash from power plant of Gongyi city of Henan province was set as a study object.A kind of zeolitic adsorbent for denitrification and dephosphorization has been synthesized by using the alkali fusion-hydrothermal synthesis method from fly ash and the wastewater was processed keeping with the standards by using this zeolitic adsorbent.Details were as follows:(1)The analysis of fly ash.The physical and chemical properties and adsorbability of fly ash were analyzed by laser particle size analyzer,x-ray diffraction,scanning electron microscope,surface area analyzer and nesslers reagent spectrophotometry,ammonium molybdate spectrophotometry.The results showed that:the partical size of fly ash was mainly between 9.98 μm and 36.08 μm,and its spherical particles were more regular.It has the capacity of physisorption because of there were gaps among balls.The main mineral composition including the glass phase and crystal material,the crystal material was mullite and quartz and the main chemical composition was SiO2 and Al2O3.The fly ash had a certain surface area and small cation exchange capacity only for 23.10 mmol/100 g,so it could adsorb the ammonia nitrogen and phosphorus in wastewater but the capacity of adsorption was limited.(2)The study of synthesis of zeolitic adsorbent for denitrification and dephosphorization from fly ash.P type zeolite was synthesized from fly ash by using the alkali fusion-hydrothermal synthesis method The synthesis conditions were studied by method of single factor experiment with the effect of mixing ratio(0.8:1,1.0:1,1.2:1,1.5:1),the calcination temperature(450℃,500℃,650℃,750℃)and the alkali-water ratio(1:15,1:20,1:25,1:30,1:35)in hydrothermal reaction.The optimal synthesis method was obtained by analyzing and testing the cation exchange capacity of the synthetic.The results showed that the conditions of synthesizing zeolitic adsorbent for simultaneous denitrification and dephosphorization were that:the mixing ratio was 1.2:1,the calcination temperature was 650℃ and the alkali-water ratio was 1:25.In this condition,the cation exchange capacity of zeolitic adsorbent increased to 262.4 mmol/100 g.(3)The application of the zeolitic adsorbent in wastewater.The effect factors in the process of adsorption were discussed and the adsorption isotherm model and dynamics model were simulated.The results showed that:The removal of ammonia nitrogen was mainly based on cation exchange and the removal of phosphorus was mainly based on chemical precipitation.ZFA had a high adsorbability of phosphorus in ammonia-nitrogen wastewater.The removal rate of ammonia nitrogen was 88.37%when the solid-liquid ratio was 0.02 in 150 mg/L ammonia-nitrogen wastewater.The removal rate of ammonia nitrogen decreased with the temperature increased.ZFA had higher removal rate of ammonia nitrogen when the initial pH was 7-8,and the rate would decrease in environment of acid or alkaline.The concentration of Na+in wastewater had a certain effect on the removal of ammonia-nitrogen.The adsorption process in ammonia nitrogen was according with first-order kinetics at room temperature and the adsorption isotherm could be described by Freundlich equation at room temperature. |
