| dc.description.abstract | The fly ashes generated from incineration and metallurgical processes have been classified as a hazardous waste. In this study, sequential extraction procedure, TCLP and aqua regia extraction were used to explore chemical bondings and heavy metals in fly ashes generated from different steel industries and municipal waste incinerators (MWI). The potential impact of heavy metals leached in different leaching processes on the environment was investigated. In addition, the effect of acidic agents on total TEQ of dioxin in the collected ash samples was investigated by analysis of PCDD/F contents in residues collected from each fraction of sequential extraction.
The results indicate that different chemical bondings and leaching characteristics of collected ash samples were observed and relied on steel-making materials, types of steel industries, types of steel-making furnaces, and operating parameters. Cadmium was mainly leached out from the first three steps (water-soluble, ion-exchangeable, and hydroxides and carbonates fractions) (Plant A: 93.6%, Plant B: 43.1%, Plant C: 70.8%, Plant D: 66.5%) and should be noticed during treatment due to its high mobility. The bonding structure of leached lead was performed differently based on the basic characteristics of ash samples. The results of heavy metals obtained from TCLP showed that the leached cadmium concentrations of collected ashes were 41.0, 6.84 and 23.7 mg/L, respectively, for Plant A, B, and C. These concentrations all exceeded the regulated standard. The leached lead concentrations for Plants A, B, C, and D were, respectively, 165, 83.2, 7.92, 9.83 mg/L, which were all over the regulated standard as well. The distributions of 17 toxic PCDD/Fs extracted from residue using sequential extraction procedure were found no difference in first five different extraction fractions (water-soluble, ion-exchangeable, hydroxides and carbonates, amorphous Fe-Mn oxides and crystal Fe oxides), and their concentrations were all below the regulated standard (1.0 ng I-TEQ/g). The highest concentrations of dioxin in the residue were found at the 6th extraction step（sulfide fraction）and this demonstrated the sufficient ability to leach a large amount of PCDD/Fs by using strong oxidants and acids at the sulfide fraction. | en_US |