Enhancing waste treatment: Co-melting of MSWI fly ash and biomass ash for lower melting point and efficient vitrification

High-temperature melting is a promising approach to converting municipal solid waste incineration fly ash (MSWI FA) into environmentally safe vitrified slag. However, the process is hindered by high energy consumption and incomplete vitrified products. This study proposes a co-melting strategy, blending MSWI FA with straw ash (SA) and rice husk ash (RHA), to simultaneously reduce the melting temperature and produce vitrified products enhancing the slag's environmental safety. Experimental results reveal that optimal additions of SA (20–50 %) and RHA (20–40 %) significantly lower the melting point of MSWI FA by approximately 100 °C and facilitate the formation of stable vitrified phases. Through a combination of co-melting experiments and thermodynamic simulations, the mineral transformation, vitrified slag formation, and heavy metal stabilization were examined. Key conditions for complete vitrification were identified, including maintaining temperatures at or above the flow point and ensuring a liquid phase content exceeding 50 %. Furthermore, leaching tests confirmed the effective immobilization of heavy metals below regulatory limits. The co-melting of MSWI FA with biomass ash reduces energy consumption, and facilitates the transformation of MSWI FA into harmless materials. This study provides a sustainable solution for advancing “waste-treat-waste” technologies, offering an effective approach to enhancing waste treatment.