Distribution, Leaching Behavior, and Mobility of Heavy Metals in Fly Ash from Grate‐Fired and Fluidized Bed Municipal Solid Waste Incinerators

This study systematically investigated the distribution and leaching behavior of seven heavy metals (Pb, Cd, Zn, Cu, Cr, Ni, and Hg) in fly ashes collected from four municipal solid waste incinerators, comprising two grate‐fired and two fluidized bed systems. The total concentrations of heavy metals were significantly higher in grate‐fired fly ash, with Zn and Pb reaching up to 6,526 mg/kg and 3,412 mg/kg, respectively—over 70% higher than those in fly ash from fluidized bed incinerators. While finer particles (<43 µm) exhibited the highest metal concentrations per unit mass, medium‐sized particles (43–138 µm) accounted for the majority (>70%) of total heavy metal mass, highlighting their dominant role as metal carriers. Leaching tests revealed that Cd exhibited the highest leaching rate (∼80% under NEN7341), followed by Zn (∼50%) and Pb (∼30%), especially under acidic conditions. In contrast, Hg showed strong retention with leaching rates consistently below 10%. Notably, the leaching behavior was independent of particle size and primarily influenced by leachant chemistry. These findings provide new insights into the influence of incinerator type and particle size distribution on heavy metal mobility in fly ash.