Characteristics of Municipal Solid-Waste Incineration Fly Ash with High-Temperature Melting and Vitrification

This study aims to determine the melting and vitrification characteristics of waste incineration fly ash. For this, the fly ash was melted via gradual heating in a vertical tube furnace, which was followed by stratification. The upper layer of the melt comprised molten salt, while the lower layer of the melt comprised slag. Moreover, a vitrification experiment was conducted on slag and SiO2 as an additive. After water quenching, experiments were conducted under different alkalinity conditions to study the vitrification properties of the fly ash. The main three phases of the bottom slag after high-temperature melting of fly ash are CaO, Al2O3, and SiO2, with CaO content being 49.60%. By introducing SiO2 to adjust the binary basicity (R=CaO/SiO2) within a mass ratio range of 0.5–1.5, it was found through quality adjustment experiments that the mixed slag completely vitrified [X-ray diffraction (XRD) shows no crystalline peaks] after melting at 1,450°C for 2 h when R was 0.5–1.25. However, the vitrification degree decreased to 86.9% when R reached 1.5. The slag obtained using quartz as an auxiliary material comprised mainly the SiO2–Al2O3–CaO slag system. The vitrification composition of the slag system was determined under alkalinity of 0.5–1.25, and the composition range was indicated on the ternary phase diagram. Melting vitrification using additives and fly ash slag was proven to be a feasible technology for final safe disposal of municipal solid-waste incineration fly ash. The results of this study can guide enterprises to regulate fly ash and realize fly ash vitrification in actual industrial production.