Detoxification, solidification and recycling of municipal solid waste incineration fly ash: A review

Municipal solid waste incineration (MSWI) fly ash, containing heavy metals and dioxins that can migrate and accumulate in biosphere, poses severe threats to human health and the environment. This review summarizes the sources and characteristics of heavy metals and persistent organic pollutants in MSWI fly ash, and comprehensively compares and discusses various treatment methods of MSWI fly ash, such as thermal treatment, pyrolysis process, hydrothermal treatment, solidification/stabilization (S/S) method and leaching process. Besides, the mechanism of dioxins degradation, and the principle of heavy metals solidification and recovery are analyzed in detail. Moreover, the pre-removal methods of chlorides are compared due to their adverse effect on the treatment processes of MSWI fly ash. However, to date, most of the disposal processes only have good effect on dioxins or heavy metals, except for pre-washing thermal treatments (sintering, melting and vitrification etc.) which need high energy consumption and complex equipment. Finally, low-temperature catalytic pyrolysis with electrolytic manganese residue (EMR) and S/S combined process of MSWI fly ash, and collaborative treatment of MSWI fly ash with melting furnace to degrade dioxins and enrich heavy metals are proposed. Those can provide some reasonable development directions for a completely harmless treatment of MSWI fly ash based on the comprehensive analysis of all hazardous components.