The Characteristics Of Ash And Slag In Waste Incineration Power Plant Of Xiamen And Heavy Metals Distribution In This Process

The incineration of municipal solid waste(MSW)produces a large amount of slag and fly ash,which contains many harmful substances such as heavy metals and belongs to hazardous waste.In present study,the samples of incoming MS W,fly ash,slag,leachate and flue gas were analysed and assessed from the three MSW incineration power plants.Moreover,the migration and transformation of heavy metals in this process were discussed.The research results are as follows:The garbage in Xiamen is mainly made of paper,rubber and plasticin Houkeng Plant,Xiang'an Plant and Haicang Plant,which accounts for 84.23%,82.92%and 71.39%of the total waste respectively.The moisture content of waste is about 56.25%.The chemical elements,composition and surface morphology of fly ash,slag were analyzed by X-ray fluorescence spectrometer and scanning electron microscope.The results were shown that the main compotents of the fly ash were Ca(OH)2?CaCO3?CaSO4?SiO2.The basic elements were oxygen,calcium,chlorine,silicon.The average content of heavy metals such as copper,lead,zinc,iron,etc.was less than 1%.The fly ash samples were more cemented,mainly in the form of crystals.The particles size distribution was mostly tens of microns or more.The properties of slag were similar to fly ash.The mineral phase of fly ash and slag was also assessed by X-ray diffraction spectrometer.The results were shown that the fly ash crystal components were mainly silicates,chlorides,sulfates and carbonates such as Ca(OH)2,CaCO3,CaSO4,SiO2,NaCl,KCl,Na2S04,Mg(OH)2,SiCl4,Ca2SiO5(OH)2·H2O,NaCa2.5(Si10Al6)O32·14H2O.The slag crystal components were mainly compound containing calcium and silicon such as CaCO3,Ca(OH)2,SiO2,Ca2SiO4 Ca3Si2O7.The heavy metals were mainly distributed in fly ash and slag,however,a small fraction of heavy metals was migrated to the leachate after wastc incineration.Only a little amout of heavy metals was in the flue gas.The concentrations of heavy metals in each component were analyzed.The results were shown that the order of heavy metal content in the waste was Zn>Cu>Pb>Cr>Ni>Cd>Hg,and the components were shown the same trend.However,the order of heavy metal content in leachate was Fe>Zn>Mn>Cr>Cu>Ni>Pb>Cd>Hg.In fly ash,the distribution proportion of Hg and Cd is the largest,accounting for 100%and 81.65%on average.In slag,the distribution proportion of Ni,Cu,Ba and Cr is the largest,accounting for 95.86%,94.48%,91.1 1%and 90.54%on average.The leaching heavy metals of fly ash and slag were analyzed by flame and graphite furnace atomic absorption spectrometer.The results were shown that the fly ash had a lot of heavy metals,especially Pb and T-Cr were easy to leach,which exceeded the national standard and belongd to hazardous waste.Thus the fly ash could be landfilled after stabilized or solidified treatment.The slag had low heavy metal content and the leaching concentration was less than the limit of Table 1 of GB 5085.3-2007,which belonged to general solid waste.