Development And Research Of Recycling Technology Of Waste Fly Ash Based On Environmental Protection Concept

Municipal solid waste incineration fly ash(hereinafter referred to as "fly ash")as a high surface area material.It is rich of toxic heavy metals such as Hg,Pb,CD,Cu,Zn,Cr and so on,dioxins and furans.It is constituting the potential threat to the underground water,the surrounding ecological environment and human health.In addition,fly ash also contains large amounts of the soluble salt.It has great influence on the pavement performance of asphalt mixture.At present,the ways of the fly ash disposals are: the sintering pretreatment,the washing pretreatment,the chemical medicament solidification,the cement solidification,the melting and so on.after those proper disposal to landfill.Thesis adopts the method of washing pretreatment,adopts the solid-liquid ratio of 1:2,1:3,1:4,1:5 and washing for once,twice,three times to pretreat the original fly ash.Using potassium chromate as indicator and the method of silver nitrate titration of chloride ion.Test the content of chloride ion in the filtrate and chloride ion in the fly ash powder after washing.Conclude the removal effect of soluble salt in fly ash by the method of washing pretreatment.Then substitute washed fly ash for cement adding into cement stabilized macadam and concrete.According to the mechanical properties,the results of dry-shrinkage tests,abrasive resistance tests etc,and in combination with the washing process,washing dechlorination rate,economy and other factors,selecting the optimal parameters of the washing;finally,on the basis of the optimal parameters of the washing analyzing the performances of cement stabilized macadam and concrete which are mixed by washed fly ash asphalt mixture material.The performances includes material with high temperature stability and low temperature crack resistance and other performances.Through mix proportion design,selecting the optimal mix proportion of cement stabilized macadam and concrete mixed by fly ash.The results show that the original fly ash chlorine content is 13.3%,the lowest chlorine content in washed fly ash powder decline to 0.9%,the chlorine removal rate can reach as high as 92.8%;by freeze-thaw splitting test conclude that the fly ash in 1:3,1:4,1:5 and respectively washed more than twice added into asphalt mixture and the water stability could meets the requirements specification;considering washing water economy and secondary sewage treatment of economy confirming that 1:3 and washing 2 or 3 times will be the optimal parameters of the washing;the washing pretreatment fly ash with optimal parameters adding into cement stabilized macadam and concrete could performance high temperature stability and low temperature stability that meet specification requirements.