Study On The Recycling Of MSWI Fly Ash

At present,more and more cities in China are confronted with the phenomenon of garbage siege.The incineration of municipal solid waste has become one of the main ways of waste disposal in China because of its characteristics and advantages such as reduction,harmlessness and resource utilization.Waste incineration process will produce a lot of fly ash,fly ash due to the accumulation of heavy metals and dioxins and other toxic pollutants,China and many other countries in the world clearly defined as hazardous waste.The disposal of fly ash is mainly based on landfill,however,the fly ash has a potential for resource utilization.In view of the problems existing in the research of fly ash washing pretreatment and resource utilization,this paper carried out the experimental study on the washing of MSWI fly ash,the treatment of fly ash and the preparation of aggregate incineration,the main research contents and conclusions are as follows:1)Based on the physical and chemical properties of fly ash,the experiment was carried out to study the water washing of fluidized bed fly ash and grate fly ash.The results show that most of chlorine in fly ash existed in the form of soluble chloride salt,such as NaCl,KCl and CaCl2.Most of the chlorides can be removed by water washing.The fly ash in the fluidized bed can reach 77.1%by one washing.The fly ash from the grate furnace can reach 94.3%after one washing.The optimal conditions of single washing:the washing time of CFB fly ash was 30min,washing liquid to solid ratio was 6(mL/g);the washing time of grate fly ash was 30min,washing liquid to solid ratio was 8(ml/g).For the fly ash in fluidized bed,the effect of two cycles of washing water and the two water washing is not much difference,but the effect of water saving of the two cycle is obvious,so the method has better economy.In addition,the chlorine content of the fly ash washing liquid is as high as 6000～28000mg · L-1,cannot be directly discharged,need to be further processed.2)The experimental was carried out to study on the washing solution of CFB fly ash which contain high chlorine content.The results showed that the removal rate of chlorine was 50.7%after chemical precipitation.Adding chemical reagents can further remove chloride water solution,but the promotion effect is not obvious,and disposal costs will increase significantly.Fly ash washing solution membrane separation treatment results show that the removal rate of chloride ion decreases with the increase of the ratio of the shade to the total amount of water,and the removal rate of chloride ion increases with the increase of the operating pressure.The aromatic polyamide reverse osmosis membrane with strong physical and chemical stability,suitable for washing solution treated with strong alkaline.The removal rate of chloride ions decreases with the increase of chloride ion concentration.Combined with the technology of chemical precipitation method and reverse osmosis membrane separation technology can avoid the incomplete removal of single chemical precipitation treatment,but also to avoid the fly ash washing solution with high chlorine content blocking reverse osmosis membrane,and some reverse osmosis membrane high chlorine resistance is poor.After two-stage treatment,the removal rate of chloride ions can reach 96.74%,and the content of chlorine ions can be reduced to below 1000 mg/L,which meets the local emission standard of Liaoning Province.3)Using fluidized bed fly ash as raw material,Portland cement as binder to carry out the resource utilization of the fly ash lightweight aggregate preparation.The effects of different fly ash addition amount and curing time on the compressive strength of aggregate and the solidification and stabilization of heavy metal were analyzed.The results show that the surface of lightweight aggregate prepared by fly ash is rough,not smooth and dark gray.Aggregate outer surface is more compact,there are not connected inside the hole,was like honeycomb structure.In general,the strength of lightweight aggregate increases with the increase of cement addition,and increases with the increase of curing days.For the fly ash adding ratio is 50%,after the curing of 28 days,the strength of the aggregate can reach 1450N,the cylinder pressure is 4.34MPa,which meets the requirements of "light aggregate and its experimental method GB/T17431.2-2010".At the same time,the leaching amount of heavy metals in the curing period is lower than the limit value of GB 16889-2008,which indicates that it is feasible to prepare the lightweight aggregate by fly ash and cement.For the fly ash after ball milling,the strength of the aggregate is higher than that of the washed fly ash,and the leaching amount of heavy metal is also lower than that of the washed fly ash.Therefore,the aggregates prepared by ball-milled fly ash have better product quality,and the cost of milling should be taken into account.