Influence of SiO_2 Additive on Melting Characteristics from MSW Incinerator Fly Ashes

Mixed ash samples of fly ashes from MSW incinerator, which adding additives of SiO_2 in different ratios, were carried out to determine melting treatment. Effects of the heavy metals distribution and leaching toxicity have been systematically studied. Experimental results indicate that the SiO_2 content of fly ashes have a notable influence on melting characteristics. Adding SiO_2 into fly ashes samples would effectively control the heavy metals contamination emission. For Cr, the ratio of fixation was up to the maximum 85.4% with the addition of additives about 15wt%. When adding below 15% would be of advantage to make more the heavy metals Ni, Cu, and As, stabilizing in slag. Whereas the amounts of Ni, Cu, and As, fixation in slag would decrease with the adding content of SiO_2 increasing in fly ash. For Cd, Pb, and Zn, the amounts of evaporation reduce with the adding of SiO_2 increasing. Adding SiO_2 into fly ash would validly restrain the quantity of Zn evaporation, but it have a petty effect on the controlling for the evaporation of the Pb and Cd. The amounts of Hg volatilization would be immune from altering SiO_2 content in fly ash. When adding above 20%, molten samples become full smooth, much compact in surface structure, while the sections of the molten samples have no apparent aperture. With the elevation of adding SiO_2, the shrinkage mount up, but the density decrease slowly. The leaching rates of heavy metals decrease distinctly.