Chelation treatment for heavy metals in municipal solid waste incineration fly ash: 300-Day study on stability and environmental risk

Abstract

Landfilling after chelation is the primary method for treating municipal solid waste incineration fly ash (MSWI FA), but the long-term environmental risks of its heavy metals (HMs) remain unclear. This study used three common organic chelating agents (CAs) to stabilize MSWI FA and assessed its 300-day stability under mixed and zoned landfill scenarios. The findings showed that Pb leaching posed high environmental risks, especially in zoned landfills, with 10-year cumulative leaching of 300 mg/kg, while Cu and Zn leaching remained within limits, indicating lower environmental risks. In mixed landfills, 1.6 %-TS-300, 1.6 %-SDD, and 2.4 %-DP maintained HM leaching within landfill limits but exceeded them after 220, 30, and 60 days, respectively. In contrast, when zoned landfilling, the effective time of the chelated products was significantly shortened. Under landfill requirements, chelate effectiveness was significantly shorter, with TS-300, SDD, and DP stabilizing HMs for only 30, 18, and 10 days. The study found that CAs not only form organic complexes with HMs but also precipitates (e.g., CuS) in MSWI FA, reducing leaching. Furthermore, TS-300 can convert Pb from unstable Pb⁴⁺ to stable Pb²⁺ form, enhancing its long-term stability. In summary, CAs mitigate environmental risks of MSWI FA, but HMs leaching increase over time, especially in zoned landfills. It is advised to apply a waterproof cover to chelated MSWI FA during landfilling to mitigate environmental risks.