Process And Environmental Risk Assessment For Preparing Green Bricks From Waste Incineration Fly Ash Based On Alkali Activation

Waste incineration fly ash is a by-product of solid waste incineration.It is classified as hazardous solid waste because it contains a lot of heavy metals.At present,the main treatment methods are chemical stabilization and burial after cement solidification.With the scarcity of land resources,the cost of landfill treatment is bound to increase in the future.Only by realizing the resource utilization of waste incineration fly ash,can the problem of waste incineration fly ash disposal be effectively solved.Alkali activation technology is currently used to replace traditional civil engineering materials in the world.Alkali activated slurry not only has the strong,durable and plasticity produced by cement paste cementation,but also has excellent chemical erosion resistance,freeze-thaw resistance,neutralization resistance and other characteristics.Alkali activated slurry can be used for solidification and stabilization.Harmful heavy metals in waste.Unlike the consumption of natural raw materials,high temperature forging and air pollutant discharge in the process of cement preparation,the materials used in alkali activation technology are mainly industrial by-products such as slag powder and fly ash.In addition to reducing carbon emissions and air pollution,the solid waste generated by industry can also be treated together.Based on this,this paper studies the physical and chemical characteristics of waste incineration fly ash produced by two main domestic waste incinerators,and then examines the compressive strength of brick materials prepared by alkali activation with the addition ratio of waste incineration fly ash in grate and fluidized bed incinerators under the conditions of water-washing and non-water-washing pretreatment.Finally,garbage incineration is carried out.Environmental Risk Assessment of Leaching Behavior Model of Fly Ash Green Bricks.The research results can provide theoretical and technical references for the preparation of green bricks from waste incineration fly ash and the realization of its resource utilization.At present,there are two main types of waste incinerator in our country,one is grate type and the other is fluidized bed type.The fly ash produced by the two types of grate type and fluidized bed type are also different.In this paper,it can be seen that the fly ash produced by different grate type is obviously different.Ca O:Si O2:Al2O3 in the fly ash of grate type is an element component.It is 32.83%:3.90%:1.06% and contains as much as 23.08% soluble chloride;Ca O:Si O2:Al2O3 in fluidized bed incineration fly ash is 29.62%:14.38%:5.00%,containing 5.42% soluble chloride salt,which may affect the engineering properties of subsequent alkali activation materials,on the other hand,in order to understand whether it causes waste due to different regions.In this study,a large number of fluidized bed and grate incineration fly ash from different regions were collected,and geographic information system(GIS)was used to analyze the regularity of elements composition and leaching behavior of heavy metals in incinerated fly ash.The results show that the differences in properties of incinerated fly ash come from the type of furnace bed and the leaching behavior of heavy metals.Solid waste is less relevant to the region.The compressive strength of alkali activated bricks produced by the two types of incineration fly ash under the condition of water washing pretreatment and mixing with slag powder,fly ash and alkali activating agent shows that the 28-day strength of alkali activated bricks with 20%,30% and 40% fly ash added in fluidized bed incineration without water washing pretreatment is 36.67 MPa,33.11 MPa,28.69 MPa;20%,30% and 40% alkali activated bricks without water washing pretreatment were 20.19 MPa,15.16 MPa,11.34 MPa,respectively;20%,30% and 40% alkali activated bricks with water washing pretreatment were 28.19 MPa,15.16 MPa and 11.34 MPa respectively.The daily strength of alkali-activated bricks with 20%,30% and 40% fly ash added in flushing pretreated grate incinerator is 38.25 MPa,35.27 MPaand 32.76 MPa,respectively.The 28-day strength of alkali-activated bricks with 20%,30% and 40% fly ash added is 25.05 MPa,20.46 MPa and 16.25 MPa,respectively.The main factors affecting the engineering properties are found from the subsequent microstructure and crystalline phase composition.The reason is caused by the element composition and chloride content in fly ash.The subsequent leaching test results also show that the leaching values of heavy metals in bricks do not exceed the standard limits,representing the stable state of heavy metals in alkali activated bricks.On the whole,fluidized bed incineration fly ash is more suitable for alkali activated engineering materials,while grate incineration fly ash needs proper pretreatment methods to be recycled by alkali activated technology.In order to evaluate the environmental compatibility of alkali activated bricks from incinerated fly ash,the leaching of heavy metals from fly ash and alkali activated bricks with incinerated fly ash under different p H environments was tested by the EU CEN/TS 14429 p H correlation test.The results show that the leaching types and concentrations of heavy metals in liquids of two kinds of incinerated fly ash are reduced after they are made into alkali activated bricks,and the leaching capacity tends to be consistent in acid neutralization.After a long time soaking,the basicity of the brick is released to the environment continuously.After 36 days of accumulation,the basicity of the brick decreases and stabilizes.Finally,the p H value of the brick made from grate fly ash is stable at 11.84,and that of the brick made from fluidized bed fly ash is stable at 11.24.The results of cumulative leaching of heavy metals show that all heavy metals except barium and chromium are below the quantitative limit.It is preliminarily deduced that barium is the leaching behavior mode of depletion of leaching substances,while chromium is released into leaching solution due to amphoteric element.The cumulative leaching amount of this element belongs to trace amount,so it is evaluated in environmental use.There should be no obvious harm.The comprehensive evaluation results of the benefits of three treatment schemes of waste incineration fly ash show that the order of significance is alkali activation of waste fly ash to produce green bricks,direct sintering of bricks and simple solidification landfill.This is mainly due to the high economic,environmental and social benefits of alkali activation of waste fly ash to produce green bricks,which can be produced.It has many advantages,such as valuable products,environmental improvement,low energy consumption process,large amount of waste,by-products and high utilization rate of fly ash.In view of the better economic,environmental and social benefits of the preparation of green bricks by alkali activation of waste fly ash,it is suggested that this technology be further popularized and applied.