Sintered Ceramsites from Heavy Metal-Contaminated Soil and Printing and Dyeing Sludge Fly Ash: Mechanisms of Heavy Metal Stabilization and Optimization of Sintering Conditions

• • Optimal sintering at 1150 °C for 10 min (after 400 °C preheat for 10 min) yields ceramsites with 1-h water absorption of 2.7% and bulk density of 830 kg/m³, meeting lightweight aggregate requirements while minimizing energy consumption. • • HM volatilization rates remain below 15% under optimal conditions, with residual fraction (F4) exceeding 86%, ensuring environmental safety for leachate quality. • • Sintering temperatures ≥1200 °C destabilize the ceramsite structure, leading to secondary HM release; thus, strict temperature control is critical to prevent recontamination. • • The immobilization mechanism involves physical encapsulation by the glassy phase and chemical incorporation into stable silico-aluminate lattices, effectively reducing HM mobility and leachability.