Thermal Treatment for Incinerator Ash: Evaporation and Leaching Rates of Metals

The disposal of different residues containing high concentrations of heavy metals causes environmental problems. To understand the effects of various properties of the residues on the evaporation and leaching rates of heavy metals (Cd, Pb, Zn, Cr, and Cu) by thermal treatment, three types of residues (including bottom ash, spray dryer ash, and baghouse ash) generated from various incineration conditions including spray dryer additives (SiO2, CaCl2, and NaHCO3), and feedstock additives [polyvinyl chloride (PVC), and NaCl] were investigated in the present study. The results indicated that the evaporation rate of Cd and Pb in the spray dryer ash and in the baghouse ash was higher than that in the bottom ash. The leaching rate of heavy metals in the spray dryer ash was less than 20% before the thermal treatment when Ca(OH)2 was used in the spray dryer. The addition of PVC could increase the evaporation rate of Zn in the spray dryer ash, whereas the addition of NaCl could decrease the leaching rate of Zn and Cu in the baghouse ash after the thermal treatment.