Abstract: Waste incineration fly ash, as a hazardous waste containing heavy metals and dioxins, has become a critical bottleneck constraining the waste-to-energy industry. High-temperature melting can transform fly ash into a dense glassy material, offering pathways for both volume reduction and resource recovery. In response to the challenges of significant fluctuations in fly ash composition and poor vitreous quality, a process route for preparing microcrystalline glass through plasma high-temperature melting was proposed, which regulated the composition ratio of the calcium-aluminum-silicon three-phase system in fly ash based on thermodynamic equilibrium calculations. Theoretical calculations revealed that at 1 450 ℃, the single-liquid-phase region of the calcium-aluminum-silicon system (CaO-Al2O3-SiO2) were CaO 5%-60%, Al2O3 5%-55%, and SiO2 25%-75%. Based on this, 14 different formulations（P1-P14）were developed using fly ash and coal fly ash, through experimental and characterization studies validated the glass formation efficacy. Results showed that the complete melting temperatures(1 293-1 338 ℃) of the formulations (P3, P5, P6, P9) within the single-phase region were relatively low. Calculated data for liquid phases and molten salts suggested that formulations within the single liquid phase region were more readily capable of achieving overall liquid phase transformation and vitrification at the target melting temperature of 1 450 ℃. Formulations within the single liquid phase region appeared a green, smooth, and uniform glass matrix after melting at an equipment current of 120 A (approximately 1 450 ℃). XRD results revealed that the melted product primarily exhibited diffuse peaks characteristic of the glass phase, overlaid with weak crystalline peaks such as SiO2. The elements were predominantly oxygen, silicon, calcium, aluminum and distributed uniformly. In contrast, formulations with a single liquid phase region (P1, P7) exhibited higher complete melting temperatures (1 600 ℃, 1 595 ℃). Both computational and characterization results indicated that these formulations were unfavorable for forming stable vitrified products at the target temperature. In summary, formulation adjustments based on single liquid phase regions provided a basis for thermodynamic control and stable vitrification in the fly ash melting process.

Key words: fly ash, plasma melting, thermodynamic equilibrium, calcium-aluminum-silicon ternary system, microcrystalline glass