Sustainable management of municipal solid waste incineration fly ash: A life cycle assessment based review of treatment and valorization pathways

Fly ash generated from the incineration of municipal solid waste contains high concentrations of heavy metals (Pb, Zn, Cd, Cu, etc.), soluble salts, and organic compounds, classifying it as hazardous waste. This study aims to assess the toxicity of fly ash, explore inertization treatments, and evaluate valorization pathways through life cycle assessment (LCA). Lead (Pb) was identified as the primary toxic metal, with a maximum concentration of 10,775 mg/kg of ash. In this context, the FLUREC separation process emerges as a promising alternative to conventional stabilization/solidification methods. By using acidic water to scrub incineration off-gases, FLUREC effectively extracts heavy metals and reduces environmental impact. Additionally, it was found that treated fly ash is mainly utilized in the production of construction materials. The incorporation of vitrified fly ash into cement manufacturing can reduce global warming potential (GWP) by approximately 25 % and non-renewable energy consumption (NREC) by 55 %, compared to traditional cement production. From a technical standpoint, the resulting cement mortars achieved compressive strengths above 40 MPa, meeting the requirements of the UNE-EN 998-2 standard. Economically, ceramsite production appears to be a viable option, with a net present value (NPV) of -$11.3 per ton of fly ash. These findings highlight the importance of selecting technologies based on a comprehensive evaluation of technical, economic, and environmental criteria.