Co-vitrification of hazardous waste incineration fly ash and hazardous waste sludge based on CaO-SiO₂-Al₂O₃ system

Based on the CaO-SiO₂-Al₂O₃ system, the feasibility of co-vitrification of hazardous waste incineration fly ash (FA) and hazardous waste sludge (HWS) was verified. In the CaO-SiO₂-Al₂O₃ ternary system diagram, the melting point of the system gradually decreases with an appropriate increase in SiO₂ content when the CaO/Al₂O₃ ratio is determined to be approximately 1. The TG-DSC results revealed that the liquid phase generation temperature in the FA and HWS mixture system was significantly lower than those of FA and HWS individually owing to the different CaO, SiO₂, and Al₂O₃ contents; this is consistent with the results of the theoretical melting characteristics analysis, which show that the melting characteristic temperatures can be reduced by controlling the CaO-SiO₂-Al₂O₃ ratio in the system. The co-vitrification experimental results confirmed that a vitreous content above 92%, a loss ratio on acid dissolution less than 1.74%, and leaching toxicity of heavy metals lower than 0.15 mg/L could be obtained by adjusting the CaO, SiO₂, and Al₂O₃ contents in the FA and HWS system to 20 wt%-32.5 wt%, 35 wt%-61 wt% and 14 wt%-32.5 wt%, respectively, and under a melting temperature of 1350 °C.