Speciation of Zn in WtE fly ash residues after wet treatment

Journal article, 2025

Municipal solid waste (MSW) volumes continue to increase. At a global scale, MSW is estimated to equal 3.8 billion tons annually by 2050 (United Nations Environment and Association, 2024). Non-recyclable MSW is commonly processed in waste-to-energy (WtE) facilities, allowing for recovery of energy while reducing waste volumes. WtE generates fly ash (FA) enriched in metals and inorganic compounds (Quina et al., 2018). Due to the presence of potentially toxic species, FA is typically considered hazardous waste and is disposed of in specialised landfills at high cost. However, the metal-enriched FA can be seen as a metal resource. One option for recovering metals is acid-leaching, where soluble species are separated into a liquid phase for further processing. Recovery processes for metals, mainly Zn, have been developed using this approach (Karlfeldt Fedje and Andersson, 2020, Rasmussen, 2015, Schlumberger et al., 2007). Another approach for utilising the ash is to reduce metal leachability through stabilisation at a slightly alkaline pH, since several metal ions have their mobility minimum at pH values of approximately 9–11, see e.g. (de Repentigny et al., 2018). Fly ashes with added lime are typically more suitable for this treatment, whereas ashes without lime addition are more suitable for acid-leaching.