Study On The Migration Characteristic Of Trace Element During Pyrolysis Of Municipal Solid Waste

According to a report, Chinese municipal solid waste production reached352milliontons in2010with the growth rate of8%~10%in recent years, ranking first in the world. Atpresent, there are about2/3of the cities is surrounded by municipal solid waste. Currently, thetraditional municipal solid waste disposal methods are sanitary landfill, composting andincineration, but the disadvantages of traditional unicipal solid waste disposal methods areobvious. For example, sanitary landfill ocuppy the great area of our land, the composting islow efficiency that it can only dispose a little capacity of municipal solid waste.The problemof municipal solid waste incineration is easy to result in secondary pollution, expecially thedioxins pollution. As the people’s environmental conscious are apparently improved, theydon’t satisfy the traditional methods of disposing municipal solid waste.Pyrolysis technology is a good method to dispose municipal solid waste with littlesecondary pollution and high reusability, most inpoortantly it can effectively controlemissions of dioxins pollution.Hower the component of MSW is very complex. The Pyrolysistechnology of MSW may generate by-production, which contains trace elements. In order todispose the MSW non-hardously, It is very important and necessary to realize and understandthe transfer mechanism of trace elements during MSW pyrolysis.Considering the components and distribution of municipal solid waste in our country,this paper analyzed the constituents and the source of trace elements in MSW, then measuredthe trace elements content of MSW by atomic absorption spectrometry (AAS).Meanwhile,studyed and revealed the migration characteristics during pyrolysis process, a series ofexperiments have been done using the self-designed and self-built tube furnace by changingthe atmosphere (N2, CO2, dry air,10%O2+90%N2,5%O2+95%N2), temperature (500℃～900℃), different types of chloride(NaCl and PVC), different sorbents (Kaolin mineral andCaO) and other factors which can influence the distribution and transfer of trace elements.(1)Temperature can increase the vapor pressure of trace elements, which enhances thevolatilize rate of trace elements, expecially for the volatile trace elements such as Cd, and forthe stable trace elements such as Cr, Ni, the impact is not obvious.(2) The atmospheres also have an effect on trace elements vitalization characters.Oxidative atmospheres react with the trace elements to form stable metallic oxide thatsinifically affects volatilize rate of trace elements. The transfer character of volatile Cd isn’tchanged much under all studied atmospheres. However, the oxidative atmosphere greatly decrease the volatilize rate of Pb and Zn.(3) The stypes of chlorine can effectively and differently enhance the volatility of traceelements. Pb, Cd and Zn have a higher volatilization after adding PVC, and much more Crand Ni transfer to gas-phase with the addition of NaCl.(4) Adsorbent to some extent can reduce volatilization of trace elements. CaO reacts withCl in MSW to form CaCl2that reduce trace element chloride production, decreasing thevolatilize rate of trace elements. SiO2and Al2O3in Kaolin mineral react with trace elements toform stable trace element compound, such as PbSiO3、CdSiO3、CuSiO3、ZnSiO4and ZnAl2O4.Many heavy metals are retained in the residues.