Migrationg And Transformation Of Heavy Metals In Co-processing Of Waste Incineration Fly Ash Cement Kiln Under Different Pretreatment Modes

Municipal waste incineration fly ash is classified as hazardous waste in China due to heavy metals with high leaching risk and highly toxic dioxins.Cement kiln co-processing of waste incineration fly ash is one of its resource utilization methods.Although this disposal technology can decompose dioxins and fix heavy metals,the high content of chlorine and heavy metals in fly ash can cause high-temperature clogging and skinning in cement kilns,and also reduce the quality of cement,which seriously restricts the cement kiln co-processing Development of fly ash technology.Therefore,it is necessary to pre-treat fly ash to reduce the impact of chlorine and heavy metals on co-processing technology.At the same time,the pretreatment of fly ash may affect the environmental behavior of metals in the subsequent treatment and disposal process,and the current research is very limited.Therefore,this paper explored the migration and transformation rules of heavy metals during the co-processing of waste incineration fly ash cement kilns under different pretreatment modes,and provides a scientific basis for pollution control during subsequent use.In this study,water,lactic acid,nitric acid,and phosphoric acid were selected as the pretreatment leaching solution for fly ash,and the effects of different leaching modes on chlorine and heavy metals in fly ash were studied.According to the effect of different leaching solutions on dechlorination and demetalization of fly ash,calcined materials with different chlorine content,different heavy metal content and different heavy metal forms were prepared respectively.A tube furnace was used to simulate the cement kiln,and the calcination temperature was set at 850?,950?,1050?,1150?,1250? to simulate the co-processing process of fly ash cement kiln under different pretreatment modes.The tail gas absorption liquid was collected to study the distribution rules of heavy metals in the gas-solid phase during the co-processing of different pretreatment modes.Choose 850?,1050?,1250?which represent the lower,middle and higher temperature range,and carry out the crystal phase detection on the calcined clinker.To study the effect of different pretreatment modes on the change of heavy metal morphology during the co-processing.The results showed that water,lactic acid,nitric acid,phosphoric acid leaching solution could remove soluble chlorine in fly ash.And because of the low pH of the acid leaching solution,it could also dissolve the insoluble Friedel's salt.It showed that the lower the pH,the better the removal effect of chlorine,and the dechlorination rate was 93.9%at the lowest pH of the leaching solution.Different leaching solutions had different effects on the removal of heavy metals.It might be that different leaching solutions reacted with the heavy metals in fly ash,causing the metal morphology to change,resulting in a certain difference in heavy metal content.At the same time,it was also found that heavy metals were more easily removed in the acid leaching solution,and the removal effect of nitric acid was better at 12.3%.Three kinds of heavy metals Cu,Zn and Pb with high content in fly ash were selected for tube furnace simulated cement kiln calcination experiment.The results of the study found that the nature of the fly ash after pretreatment would have a certain effect on the migration of heavy metals during the co-processing process.The chlorine content was closely related to the volatilization of the three metals in the co-processing process.A higher chlorine content was conducive to the volatilization of heavy metals.The effect of chlorine content on the volatilization of Cu was more obvious when it was greater than 1000?.15%chlorine content could increase the volatilization rate by 38.0%.The effect of chlorine content on Zn was greater at 950?,5%chlorine content was more likely to cause its volatilization than 15%,the volatilization rate differed by 14.5%.Pb was volatile,and the effect of chlorine content on the residual rate in the range of 850?1250? was obvious.The increase of volatilization rate at 1250? was 48.49%.When the initial contents of Cu,Zn,and Pb in the calcined materials were different,the higher the initial content of heavy metals,the higher the residual rate and the higher the volatilization rate.At 1250?,as the initial content of the three heavy metals increased,the volatilization rate increased between 1.98%and 7.49%.The study also found that the initial presence of heavy metals in the calcined material affected the migration of heavy metals during the co-processing.When the initial forms of Cu,Zn and Pb were phosphates and oxides,they had better thermal stability and higher residual rate.However,when the three heavy metals existed in the form of carbonate,the volatilization rates were 15.2%,48.8%,and 49.2%,which were higher than the other two forms.The nature of the fly ash after pretreatment affects the conversion of heavy metals during the co-processing.Among them,the chlorine content had a certain influence on the form of heavy metals in the clinker.When the chlorine content was less than 5%,Cu existed mainly in CuO,Cu2O,CaCu2O3,and Ca2CuO3;when the chlorine content rised to 15%,Cu2O was dominant.Different chlorine content had little effect on the presence of Zn in clinker,generally in the form of ZnO,Zn2SiO4 and ZnAl2O4.Pb existed in the form of PbO,Ca2PbO4,Pb3O4,Pb2O3,Pb6Al2Si6O21 when the chlorine content was less than 5%.As the chlorine content increased,Pb3O4 and Pb2O3 in the clinker disappear.At the same time,it was found that the initial content of different heavy metals in the calcined material had almost no effect on its existence form.The initial form of heavy metals in the calcined clinker affected its presence in the clinker.The study found that when Cu initially existed in the form of oxides,carbonates,and phosphates,the existing forms in the clinker after calcination were mainly CuO,Cu2O,Ca2CuO3,and CaCu2O3.When Zn was initially in these three forms,the three calcined clinkers generally contained ZnO,Zn2SiO4,ZnAl2O4,but the presence of Zn3(PO4)2 and Zn2(PO4)(OH)were found in phosphate clinker generate.Pb existing in these three forms,after calcination,existed in the form of PbO,Ca2PbO4,Pb3O4 and Pb6Al2Si6O21 in oxide clinker,while Pb6Al2Si6O21 disappeared in carbonate and phosphate clinker.Therefore,the initial morphology of Zn and Pb had a strong influence on the morphological transformation of heavy metals during co-processing.It could be seen that the pretreatment of fly ash not only removed a part of chlorine and heavy metals,but also the chlorine content,the initial content of heavy metals and the initial presence of heavy metals of pretreated fly ash could make a difference in the migration and transformation of heavy metals during the co-processing degree of influence.