Study On Migration Of Heavy Metals Of Municipal Waste Incineration Fly Ash In Melting Process

The incineration technology has become the most popular treatment for municipal solid wastes (MSW), for it can minimize the weight and volume of solid wastes, utilize the energy released by combustion and reduce the harmfulness. However, the incineration residues and fly ash contain considerable amounts of various heavy metals , such as Cd,Pb,Cu,Zn,Cr and so on, which would bring serious environmental pollution if without effective treatment before emission. Thus the fly ash melting treatment is proposed to solve this problem.The properties of municipal solid wastes incineration fly ash (MSWI) produced by Tongxing MSW incineration plant in Chongqing was studied by experiment, and the results show that: the average density of MSWI fly ash is 0.6723g/cm3, and its particle size is well-distributed. The MSWI fly ash has a complex composition, with CaO,SiO2 as the major constituents , separately accounting for 23.79% and 15.24% , and Al2O3,Na2O,K2O,Fe2O3,MgO as the secondary constituents. Through the heavy-metal leaching characteristic experiment, it is found that the concentration of Zn,Pb,Cd and Cr in MSWI fly ash exceed Solid Waste Leaching Character Standard. Effective treatment should be taken for MSWI fly ash.Combined with thermodynamic analysis, melting experiment was taken to study the migration of heavy metals in MSWI fly ash melting process, and fabric filter bag was applied to collect melting fly ash(MFA). The optimal melting condition was abtained: temperature for 1350℃, bisicity of 1.5, and melting period 25min. The main elements of MFA are Zn,Pb,S,Cl,K. And KCl,NaCl,ZnS,ZnO,PbCl2 constitude MFA for about 90%. Mn,Cu,Cd,Ba,As,Hg,Ti,Cr are trace elements. Hg exists with its oxychloride and sulfo-chlorinated state, and can be all collectd by condensing.The iron bath melting system can create a reducible atmosphere, which could accelerate Cr,Mn,Fe,Cu distribute out from residues into iron phase. The proportion of Mn,Fe distributing in iron phase is beyond 90%, and about 70% of Cr,Cu distribute in iron phase.The evaporation rate of Pb, Zn is separately high to about 80% and 70%, under experimental condition after 25min, and is affected by basicity and melting temperature obviously, increasing both with the increasing bisicity and the increasing melting temperature, but merely changing with melting period. The evaporation rate of Cr is very low, decreasing with the rising period.