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The content of heavy metals is found higher in fly ash than that of bottom ash, as can be seen in Table 4 and Table 5, which enlist the amount of heavy metals for fly ash and bottom ash. Of the total metal content (60,000 to 140,000 mg/kg), the recoverable metals are Zn (15,000–70,000 mg/kg), Pb (2500–16,000 mg/kg), Cu (1000 to 3000 mg/kg), and Cd (100–350 mg/kg). Accordingly, for the effective removal of heavy metals from MSWI fly ash, the addition of a certain amount of chlorinating agents with MSWI fly ash can lead to an effective removal of heavy metals. Consequently, the effort to recover heavy metals from FA varies widely is mainly dependent on metal and Al 0 content and on the ANC.
The combined treatments, such as washing-immobilization treatments, can possibly remove noteworthy quantities of sulfate and mainly chloride from incineration fly ash. The Chinese government has also set a target of disposing nearly a third of the country’s waste with waste-to-energy plants by 2030. Fly ash from municipal solid waste incineration contains a large potential for recyclable metals such as Zn, Pb, Cu and Cd.Although the recycling of waste is increasing day by day in China, there are still some challenges to face, for example, insufficient municipal solid waste separation, MSW being the dominant waste, which has a high proportion of organic components, and the separation of domestic waste is also low [ 56]. The case study by [ 18] explains the difference on the basis of heavy metal content in FA, BA and APC, and, according to [ 21], the content of Zn and Pb in China is lower than other countries, which can be seen from the Table 6. The characterization and composition of incineration ash varies over time and from region to region and country to country due to the difference in waste management/treatment practices [ 62].
Sintering involves heating the fly ash to the point at which particle bonding occurs and chemical phases in the fly ash reorganize, then the solid phase transformation and recrystallization occurs, which results in a product with lower porosity and with higher density and strength. As a basis for the development of defined recovery rates and for the implementation of the recovery process, the authorities and plant operators need information on the geochemical properties of FA. Preferentially chalcophile elements such as Zn, Pb, Cu, Sb, and Sn are expected to be enriched in FA. The working principle of the drum separator is that the pulp flows into cell body from the pulp box, and, under the water flow of the feeding spray pipe, the mineral grain will go into the feeding area of the cell body in the loose condition. The high-energy–density and high-temperature of a plasma flame can promote the melting/vitrification reactions and reduce the residence time of MSWI fly ash.The y-axis shows the distances between the calculated values and hence is a mathematical value that expresses the dissimilarity. Aluminum is usually present in FA as aluminum foil particles, which are entrained with the flue gas.
The main drawback of such a wet separation lies in the partial dissolution of the residues, especially the heavy metal compounds leaching, once they are in contact with water. The heavy metal content determines not only the choice of treatment option, but also the possible behavior of the ash during landfill or reuse.The metal content in FA depends heavily on the waste input (industrial or household waste), and elemental concentrations differ not only from plant to plant but also on a daily and seasonal basis [ 9]. This effect can be used to recover small NFe metal particles from the bulk stream (both wet and dry) [ 133]. Every city wants to win this title, but, to secure the title, cities need to achieve 85% to 90% safe MSW disposal.
Furthermore, the growing amounts of municipal solid waste are becoming problematic owing to the limited availability of land for new landfill sites. Schwermetalle aus der Flugasche Zurückgewinnen «Saure Flugaschewäsche—FLUWA-Verfahren» Ein Zukunftsweisendes Verfahren in der Abfallverbrennung; BSH Umweltservice AG: Sursee, Switzerland, 2010. From the year 2021 on, heavy metals from Swiss municipal solid waste incineration (MSWI) fly ash (FA) must be recovered before landfilling. Elemental composition was determined by energy dispersive X-ray fluorescence analysis (ED-XRF) using a Xepos spectrometer (SPECTRO, Kleve, Germany); with matrix adjusted calibration.Further major constituents are Al 2O 3 (35,000 mg/kg), Fe 2O 3 (25,000 mg/kg), P 2O 5 (10,000 mg/kg), MgO (12,000 mg/kg), and TiO 2 (17,000 mg/kg).
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