Enhancing sustainable valorization: Harmless synergistic melting treatment for high-value vitreous products from MSWI fly ash and electrolytic manganese residue.

The waste-to-energy and manganese industries face significant ecological challenges due to two major risk sources: municipal solid waste incineration (MSWI) fly ash and electrolytic manganese residue (EMR), especially, the MSWI fly is classified as hazardous waste. High temperature melting is a promising method for harmless disposal of solid wastes. However, it has yet to be industrialized due to the high costs and energy consumption. This study proposes using EMR as an additive to co-melt with MSWI fly ash, aiming to develop a method that minimizes energy consumption while producing high value-added products. To this end, the phase evolution and phase-change cooling characteristics during the co-melting process of MSWI fly ash and EMR were experimentally investigated. XRD and SEM analyses revealed that pure vitreous slag can be obtained when mixtures are heated to 1500 °C for 120 min with ≥40 wt% EMR addition under natural air-cooling conditions. Additionally, to produce vitreous slag by air-cooling and increase MSWI fly ash treatment capacity, the molten mixture with 30 wt% EMR addition was adopted in the directional solidification experiments to establish a predictive model relating the average cooling rate to the glass content. The findings ultimately contribute to the advancement of melting-based industrial applications.