Heavy metal and sintering characteristics of waste incineration fly ash: a study towards harmless disposal for fly ash within incineration plants

In-plant washing, granulation, and recycling through sintering is a promising method for the disposal of municipal solid waste incineration (MSWI) fly ash. This study focused on the effects of deacidification, washing, and flux additives on the ash melting characteristics, heavy metal content and leaching behavior during the thermal treatment of fly ash. The results demonstrate that chloride salts in the fly ash volatilize predominantly above 700 °C. Certain heavy metals (e.g., Hg, Cu, Pb) similarly volatilize at elevated temperatures. Following water washing and dechlorination, the volatilization rates of heavy metals in the fly ash decrease significantly. The high calcium content (35.20 %) of fly ash adversely affects sintering/melting processes, necessitating a flux addition exceeding 40 %. In contrast, fly ash prior to deacidification tower, with lower calcium (23.44 %) and chlorine (15.72 %) contents, requires only 10 % flux. After 1000 °C thermal treatment, the contents of Cu, Pb, and Cd in the fly ash decrease markedly. Furthermore, the quantity of fly ash prior to deacidification is approximately 54 %-70 % of the fly ash downstream of the deacidification tower, indicating that fly ash removal before the deacidification tower could significantly reduce processing requirements. By implementing simple modifications to the incinerator, such as adding a high-temperature dust collector before deacidification tower, the cost of thermal treatment can be reduced, and the feasibility of engineering applications for fly ash thermal treatment can be improved.