Competitive effects and environmental factors driving heavy metal leaching in stabilized municipal solid waste...

The widespread incineration of municipal solid waste (MSW) has raised concerns about the environmental risks of hazardous heavy metals (HMs) in fly ash (FA). Traditional FA stabilization methods rely on organic chelating agents (CAs), but the competitive interactions among metal ions and the influence of environmental factors (e.g., temperature and humidity) on chelate stability remain unclear. In this study, organic CAs were used to stabilize FA, and the leaching characteristics and environmental risks of HMs were systematically investigated under freeze-thaw cycles and dry-wet alternations. Results indicated that extreme conditions greatly exacerbated the leaching of Pb, Cd, and Zn. In particular, after 30 dry-wet alternations, the leaching concentrations of Cd and Pb reached 5.83 and 3.3 mg/L, respectively, which were 38 times and 13 times the standard limit. As the concentration differences between coexisting metal ions increased, the competitive effects between them were enhanced. Environmental factors (i.e., H⁺) had significant influences on the leaching of HMs by promoting chelate dissociation, reducing acid-resistant substances, and facilitating the transformation of HMs into unstable forms. This study, for the first time, comprehensively revealed the impact of metal-ion competition on HM leaching under extreme conditions, providing key insights for environmental risk assessment and long-term stabilization strategies.