Heavy metals removal/stabilization from municipal solid waste incineration fly ash: a review and recent trends

Waste treatment using thermal technologies, such as incineration, leads to the production of pollutants and wastes, including fly ash (FA). Fly ash contains heavy metals (HMs) and other contaminants and can potentially pose high risks to the environment and negatively impact health and safety. Consequently, stabilizing fly ash prior to either use or landfilling is crucial. The toxicity of fly ash through heavy metal leaching can be assessed using leaching tests. The leaching rates of heavy metals primarily depend on the surrounding conditions as well as fly ash properties and metal speciation. Physical separation, leaching or extraction, thermal treatment and solidification/chemical stabilization are proposed as suitable approaches for fly ash treatment. Economic considerations, environmental concerns, energy consumption and processing times can define the efficiency and selection of the treatment approach. This review considers the latest findings and compares the advantages and shortcomings of different fly ash treatment methods with the aim of highlighting the recent advances in the field. The review concludes that the simultaneous implementation of various methods can lead to highly efficient heavy metals removal/stabilization while simultaneously taking economic and environmental considerations into account.