• • Two-stage water washing removed 25.34% of water-soluble Pb and reduced soluble chlorine from 23.96% to 3.78%, lowering acid consumption in subsequent steps and facilitating heavy metal removal.
• • At 3 mol·L⁻¹, acetic acid achieved heavy metal removal efficiencies of 52.97% for Pb, 36.9% for Zn, 29.60% for Cu, and 61.54% for Cd, but caused excessive dissolution of Ca and Al; the mixed acid (acetic:sulfuric 1:1) exhibited 6.9 times higher 'calcium retention' capacity, preserving the ash matrix for construction use.
• • The combined wet process reduced heavy metal leaching concentrations to 0.001 mg·L⁻¹ for Pb and 0.05 mg·L⁻¹ for Zn, well below the GB 8978—1996 limits and meeting HJ 1134—2020 standards (soluble chlorine <1%), enabling safe on-site disposal.
• • BCR sequential extraction showed increased stable fractions of most heavy metals after treatment, indicating reduced mobility and environmental risk, while XRD confirmed formation of stable calcium-containing mineral phases.