Evaporation Of Heavy Metals During Thermal Treatment Of Fly Ash From Msw Incineration Plants

Thermal treatment method was used in this paper to remove heavy metals from MSW fly ash. Two kinds of MSW fly ash were selected from fluidized bed waste incineration power plant and grate furnace waste incineration power plant. In order to investigate the best thermal treatment scheme, potential effects had been taken into consideration. Firstly, physical and chemical characteristics of two kinds of fly ash were analysed. Secondly, the influence of thermal treatment temperature, residence time, MgCl2 additives, inlet velocity, and SiO2 was considered to determine the best operation condition for heavy metals removal. Finally, the thermal treatment of two kinds of fly ash at different blending ratios was performed in a fix bed reactor to investigate volatilization characteristics of heavy metals.The characteristics of two kinds of fly ash revealed that more than 90% of the particle size of fluidized bed fly ash was greater than 38?m. For grate furnace fly ash, the particle size was smaller and 50% of the particle size was less than 38?m. The main elemental compositions in the fly ash were Ca, Si, Al, Fe, Cl, S, K, Na, and Mg and the main crystal phase materials were CaCO3, CaCl2, CaSO4, Ca(OH)2, SiO2, NaCl, KCl, Fe2O3, etc. The sequence of heavy metals content in fly ash was as follows: Zn>Pb>Cu>Cr>Cd. The content of heavy metals in grate furnace fly ash was higher than that in fluidized bed fly ash. All fly ash had a high heavy metal leaching rate and followed the sequence: Zn>Cd>Cu>Cr>Pb.In the thermal treatment experiment of fluidized bed fly ash, heavy metal Cd, Pb, Cu and Zn exhibited higher volatility under these conditions: that is, the temperature was higher than 900? and the adequent Cl2 concentration in the reaction system, meanwhile, more than one hour and the proper inlet velocity was needed. However, Cr had a lower volatility under all conditions. From the thermal treatment of two kinds of fly ash at different blending ratios, it can be observed that Pb could be effectively removed under above conditions, regardless of the atmosphere. As for Cu, it could be removed well at a higher temperature(1000?) in oxidizing atmosphere, While the volatility was suppressed in insert atmosphere. Zn had a higher evaporation rate in insert atmosphere rather than in oxidizing atmosphere. Beside, the evaporation of Zn could be effectively promoted when grate furnace fly ash was added.