Semi-dynamic Zn leaching from solidified/stabilized dredged soil under varying curing temperatures: Kinetics and...

Elevated curing temperatures accelerate hydration and promote matrix densification in cement-based solidification/stabilization (S/S), yet whether these benefits improve Zn retention across contrasting leachants remains unclear. Zn-contaminated slurry-like mud treated with an ordinary Portland cement-ground-granulated blast-furnace slag binder was cured at 20, 40, or 60 °C and subjected to accelerated semi-dynamic leaching in deionized water (DW; pH ∼7.0), sulfuric/nitric-acid simulated acid rain (SN; pH = 3.20), and acetic acid (AA; pH = 2.88). Results reveal a fundamental trade-off: elevated temperatures refined the pore structure and shifted Zn toward less labile fractions, but reduced alkaline buffering and lowered leachate pH under DW and SN. Under DW, heat curing suppressed Zn release by increasing resistance to diffusive transport through the hydrated matrix (D_e ≈ 10^-18-10^-17 m² s^-1). Under AA, Zn release was dissolution-dominated at all temperatures; strong Ca-Zn coupling and 94-98% outer-layer Ca/Si depletion supported matrix decalcification and mobilization of matrix-associated Zn. Notably, under SN, earlier buffering depletion advanced the transition from diffusion-dominated to dissolution-dominated kinetics below an empirical leachate-pH transition point of ∼4.4. Near-zero Ca-Zn coupling and SEM-EDS/TG-DTG evidence supported preferential acid-labile Zn mobilization with localized near-surface decalcification. Maximum interval-mean Zn concentrations were 0.164-0.325 mg L^-1 under SN and 4.418-6.456 mg L^-1 under AA; concentrations under SN remained below the Chinese Class II groundwater Zn limit of 0.5 mg L^-1. These findings demonstrate that curing temperature shifts the balance between transport resistance and buffering capacity, providing a mechanistic basis for matching curing strategies to exposure chemistry in engineering design.