Study On Phosphorus Adsorption And Detoxification And Damage Reduction Of Municipal Solid Waste Incineration (MSWI) Fly Ash

At present,most cities in China are facing the crisis of“garbage siege”,waste incineration technology has been listed as the major method for municipal solid waste?MSW?treatment during the 13th Five-Year Plan period.However,during MSW incineration,it will produce about 69.9-91.5%of dioxins which enriched in fly ash.Therefore,municipal solid waste incineration?MSWI?fly ash is recognized as a hazardous waste.So processing methods for detoxification and hazardous reduction of MSWI fly ash need to be carried out urgently.This paper based on the porous structure,large specific surface area and higher content of CaO in fly ash,and treat it as a adsorbent to adsorb phosphorus-containing wastewater which simulated in laboratory,and microwave medium temperature degradation technology was used to reduce its toxicity.The effects of adsorbent dosage,solution pH values,adsorption kinetics,adsorption thermodynamics,adsorption isotherm and coexisting ions on phosphorus were studied and different materials were characterized;finally,PCDD/Fs in fly ash were treated by microwave pyrolysis technology.The main research contents and results of this paper are as follows:?1?The results of material characterization showed that the surface of the original fly ash is uneven and its structure is loose,it is advantageous to improve the adsorption effect of fly ash on phosphate;after adsorption of phosphate,the structure of fly ash particles get loose.?2?The adsorption experiments show that:pH values of solution is the key factor which affecting the adsorption of phosphate by fly ash;the optimum dosage of fly ash to phosphate is 0.5g/L;adsorption of phosphate by fly ash fit in with pseudo-second-order kinetics model;thermodynamic experiments showed that the process of phosphate adsorption by fly ash is endothermic and spontaneous;the fitting of Langmuir and Freundlich adsorption isotherm model showed that the adsorption of phosphate by fly ash conforms to Langmuir isotherm model,the maximum adsorption capacity of fly ash to phosphate was 114.35 mg/g;CO₃^2-and Mg²⁺had obvious inhibition effect on phosphate adsorption;chemical precipitation played a dominant role in the process of phosphate adsorption.?3?The experimental results of dioxin treatment by microwave irradiation suggested that:when the ratio of silicon carbide to the original fly ash,the fly ash on the screen and the fly ash under the screen is 9:1 and the amount of thiourea is 0.2g,respectively,the degradation efficiency of dioxins in fly ash are all reached 99%;while when the ratio of silicon carbide to fly ash dried by freeze-drying and oven-drying is 9:1 and 0.2 g thiourea is added,the reaction time is 15 min and 14 min,the highest temperatures of fly ash samples irradiated by microwave are 328.0 and 337.7 respectively,and the degradation efficiency of dioxins in fly ash is 28.7%and 31.3%respectively.when the ratio of silicon carbide to wet fly ash adsorbed phosphorus and filtered are 8:2,9:2,10:2 and thiourea is not added,the degradation efficiency of dioxins in fly ash are-40.2%,76.6%,88.1%,respectively;however,when the ratio of silicon carbide to wet fly ash adsorbed phosphorus and filtered is 10:2 and the amount of thiourea are 0.2g and 0.5g,the degradation efficiency of dioxins in fly ash reaches more than 98.0%,respectively,among them,the latter only took about 8 minutes.?4?The degradation mechanism of PCDD/Fs in fly ash by microwave pyrolysis showed that:the presence of silicon carbide in fly ash can significantly promote the absorption of microwave energy on fly ash surface,it is advantageous to improve the degradation of PCDD/Fs in fly ash;meanwhile,thiourea added to fly ash is decomposed by microwave pyrolysis to produce NO₂ and SO₂,thus,the formation of PCDD/Fs in fly ash is inhibited.