The increasing generation of municipal solid waste incinerator (MSWI) fly ash, classified as hazardous waste due to its high content of heavy metals and soluble salts, poses a significant environmental challenge. Traditional disposal through landfilling is becoming increasingly unsustainable, not only because of the declining availability of landfill capacity, but also owing to the risk of pollutant leaching and long-term environmental contamination. In the context of the circular economy, the transformation of MSWI fly ash from a waste product into a valuable secondary raw material represents a strategic priority. However, the highly heterogeneous composition of fly ash complicates its handling and disposal, often requiring tailored management pathways depending on its physicochemical characteristics.