Leaching of Heavy Metals from Fly Ash Generated from Gasification and Melting Furnace for Municipal Solid Wastes by Organic Acids

The leaching behavior of zinc, lead, and copper from fly ash generated in gasification and melting furnaces for municipal solid wastes (MSW) was studied by a constant pH leaching method with organic acids. The leaching degrees of the above-mentioned heavy metals were as low as 10%, or lower at pH 2 for the residue, obtained by leaching fly ash with water. The leaching degree of heavy metals increased remarkably with the addition of organic acids. The leaching degrees of zinc, lead, and copper were 64, 64 and 91%, respectively, under conditions where the concentration of citrate was as low as 0.001 M, and pH was 4. The citrate's effectireness in the leaching of heavy metals may be due to the catalytic acceleration action of dissolution, but not the stabilization effect for heavy metals in solution. The degree of leaching for zinc, lead, copper, and silicate decreased with the elevation of the reaction temperature from 25°C to 50°C. A constant pH leaching method with citrate has features such that high leaching degrees for heavy metals are obtained, and silicate gel, which is difficult to be filtered, is not generated.