Leaching Agent and Iron Distribution Co-Treatment Regulates the Distribution and Migration of Pollutants in Heap-Leached MSWI-BA

This study investigated the combined effects of leaching agents and iron distribution on the migration behavior of pollutants in municipal solid waste incineration bottom ash (MSWI-BA). A column leaching experiment was designed where the control group (CK) employed deionized water with uniformly distributed iron. This baseline was systematically compared against treatment groups involving two leaching agents (Na 2 CO 3 , Na 2 SO 4 ) and three iron distribution scenarios (Top, Bottom, and Removal). Compared to the CK, the introduction of Na 2 CO 3 significantly intensified pollutant mobilization: the abundance of microplastics (MPs) increased by 49.33%, chloride leaching rose by 189.99%, and heavy metal (HM) concentrations (Cu, Cr, Pb, As) surged by 2.0–40.6 times. Furthermore, iron distribution played a critical regulatory role; specifically, manipulating iron placement further elevated MP abundance by 80.2% and chloride leaching by 191.03%. Morphological analysis indicated that MPs primarily existed as transparent or yellow particles, films, and fibers, characteristics that remained stable across treatments. Crucially, these findings offer engineering insights for real-world scenarios: retaining a bottom iron-rich layer during stockpiling can act as a reactive barrier to intercept pollutants, whereas carbonate-rich landfill environments require pH-buffering to mitigate MP co-migration. This study provides a theoretical basis for optimizing pretreatment processes (e.g., coordinated washing and magnetic separation) to ensure the safe resource recovery of BA.