Abstract: The fly ash from the co-incineration of municipal sludge in the grate furnace of a MSWI was used as an experimental sample. The total amount of heavy metals and leaching characteristics of fly ash produced by mixing sludge were analyzed and compared. The results showed that compared with zero mixing firing， co-incineration of municipal sludge reduced the total amount of heavy metals in fly ash， while the residual alkalinity of fly ash was significantly reduced because the SOx produced by mixing sludge consumed alkaline agents， leading to the low leaching pH of 5.27. The corresponding leaching concentration of heavy metals such as Pb and Cd was much higher than the limits of GB 16889—2008 Standard for Pollution Control on the Landfill Site of Municipal Solid Waste. Addition of 10% limestone into fly ash could increased the residual alkalinity， indicated by a higher leaching pH of 6.32 and the leaching concentrations of Pb,Zn,Cd,As were lower than the limits of GB 16889—2008. While mixing the sludge， the amount of deacidification agent feed into the flue gas purification system was suggested to be flexibly adjusted， which would contribute to the leaching stability of fly ash.

Key words: waste incineration, co-incineration of sludge, fly ash, the leaching of heavy metal