Leaching Behavior Of Chlorine And Heavy Metals During Carbonated Washing Of MSWI Fly Ash

MSWI fly ash is a hazardous waste produced by incineration,with high chlorine content and heavy metal leaching toxicity,which is the main factor restricting its resource utilization.At present,washing is one of the mainstream disposal methods to treat waste incineration MSWI fly ash to remove most chlorine elements in it.However,there are still some key problems in this method,such as low degree of dechlorination,large amount of wastewater and high heavy metal concentration.Taking MSWI fly ash of grate furnace as the main research object,this research introduces the CO₂ in washing process and discusses its dechlorination effect.Study on heavy metal migration in MSWI fly ash carbonation washing process The main conclusions are as follows:The dechlorination rate of MSWI fly ash in waste was determined by using liquid to solid ratio of 2:1,3:1 and 4:1,respectively 50.50%,63.34%and 70.18%.The dechlorination rate increased to 86.30%,90.83%and93.15%,respectively.Increasing the natural ratio of washing solution to washing frequency washing frequency promote Chlorine removal,but still1%insoluble chlorine salt remains in fly ash after repeated washing.On the basis of this,the influence of carbon CO₂ input,liquid-solid ratio and washing times on dechlorination was investigated.Changes in CO₂flow to regulate the p H of the slurry resulted in maximum the dechlorination rate at 6-7 p H with liquid-solid ratios of 64.93%,74.62%and 77.77%,respectively,14.43%,11.28%and 7.59%higher than conventional washing.The dechlorination rate was 91.20%,93.60%and94.20%respectively under the condition of three liquid-solid ratio,which was 4.90%,2.77%and 1.05%higher than that under the condition of secondary carbonation.After repeated carbonization of fly ash,the residual chlorine content decreased to 0.64%.The main reasons for the increase of carbonization and dichlorination rate of fly ash are analyzed.Carbonization promotes the decomposition of insoluble chlorine salts,reduces the water content of fly ash residue,improves stirring effect and enhances the dechlorination of fly ash water.The solubility behavior of heavy metals in MSWI fly ash carbonated water also changed with the decrease of p H and action of CO₃^2-in purifiers.Pb ions concentration in bicarbonate of water decreased from 81.07 mg/L to 36.26 mg/L and Cr ions concentration decreased from 0.44 mg/L to 0.01mg/L,indicating a significant decrease in Pb and Cr ions concentration compared to conventional washing process.The concentration of Cd ions and Mn ions in water purification solution increased.