dc.description.abstract | This study investigated the feasibility of municipal solid waste incinerator (MSWI) fly ash melting by industrial waste Al dross and electric arc furnace (EAF) dust as a waste-derived-Thermite (WDT) reaction. The best ratio of Al dross and EAF dust are examined under different atmospheres. The fate of heavy metals is discussed by varying fly ash content and atmospheric compositions.
The Gibbs energy was calculated to confirm between experimental results and prediction by a thermodynamic model. The results indicated that speciation and partitioning of heavy metals are affected by the presence of chlorides. As the reacting temperature varies from 1500℃ to 2000℃, the most stable species in the slag are NiO, Cr2O3, ZnO, CuO, Cu2O, PbO and CdO, and the most stable species in the flue gas are PbCl2(g), PbO(g), Cd(g), ZnCl2(g), and CdCl2(g).
The best ratio of Al dross/EAF dust yielding the maximum of heat is 0.47 by weight. The maximum temperature of the WDTs reaction is 2082℃ under air, and 1873℃ under N2. Ingots presented 30% of the reaction output in air, and 15% in N2. The purity of iron in the ingot are 80.44% and 83.43% under air and N2, respectively. Partitioning of Fe in the ingot are 91.15% under air and 65.94% under N2, respectively.
The self-propagating characteristics of the Thermite treating MSWI fly ash was evaluated by varying the fly ash content in the starting mixture (27.73g Al dross/ 60g EAF dust) from 10g to 40g. The results indicate that the content maximum of fly ash less than 40g at this ratio. The reaction temperature decreased with increasing fly ash content. The slag recovered showed stable vitrified structure with lowest TCLP leaching concentrations of heavy metals complies with current regulatory thresholds at 20g fly ash added. The partitioning of heavy metals was determined in this study. Cr, Cu and Fe mainly transferred to the ingot. Pb and Ni mainly transferred to flue gas and slag. Zn and Cd evaporate to flue gas easily. Pb, Cu, Cd, Zn and Ni evaporate easily and adsorbed by secondary fly ash at higher reaction temperature. | en_US |