Speciation Of Lead And Chromium In Second Fly Ash Of Municipal Solid Waste

Waste incineration fly ash is a kind of hazardous waste,whose main disposal are secure landfill and resource utilization.Before secure landfill or resource utilization,fly ash need stable curing pretreatment to make heavy metals fixed in the cement,asphalt and other materials in the maximum limit by physical and chemical reaction,which methods are melting solidification,cement solidification and chemical stabilization.However,heavy metals in derivatives after processing those methods still pose a potential hazard to the environment considering from the long-term environment safety.High temperature thermal separation technology can make the most of the volatile matter of heavy metals in fly ash condensated second fly ash with flue gas.The ash after high temperature separation can be used as ordinary waste landfill or as a raw material such as buildings and roads and higher content of heavy metals in fly ash can be used as metallurgical materials for heavy metal recycling.The ultimate goal of this experiment is to study the recovery of heavy metals in incineration ash.Based on the research of basic features of secondary fly ash and incineration fly ash,this experiment discussed the main factors affecting the burning of volatilization of heavy metals in fly ash and studied the chemical speciation of lead and chromium in the form of heavy metals in fly ash.This experiment provides a detailed and reliable data for the volatilization mechanism of heavy metals.In this paper,by using X-ray absorption fine structure,it studied geometrical shape of Pb and Cr in secondary incineration fly ash and fly ash and the percentage content of lead compounds and chromium compounds in the sample are given respectively,as well as the lead and chromium valence state,coordination number,bond length and so on.The results of XAFS experimental show that the PbO and Pb3O4 content in the fly ash accounted for 47.5%and 22.5%respectively in lead compounds of the sample,there is also a small amount of PbSO4,PbCl4 and PbS.The content of PbCl2 in the five kinds of fly ash samples accounted for about 50%in lead compounds of the sample,the content of PbS accounting for 20.2?36.2 is high.In addition,it also contains a small amount of PbO,Pb3O4,PbSO4.The content of Cr2O3,CrO3 and CrO2 in incineration fly ash accounted for 69.7%,22.5%and 7.8%respectively in chromium compounds of the sample.Cr mainly existed in form of Cr2O3 and CrCl3-6H2O in the four types of second fly ash,and a small amount of CrO2.Among them,with the increase of temperature,the account of chromium compounds gradual increase in the proportion of CrCl3·6H2O in the sample.In this research,it shows that heavy metals in secondary fly ash mainly exist in the form of chloride.It can conclude that the chloride has played a major role in the process of volatilization of heavy metals.