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 (Na2CO3, Na2SO4) and three iron distribution scenarios (Top, Bottom, and Removal). Compared to the CK, the introduction of Na2CO3 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.