• • Optimal single-stage water leaching achieved 87% Cl removal at liquid-to-solid ratio 5 mL/g, 70 °C, 60 min, and 160 r/min, demonstrating a simple, cost-effective dechlorination route.
• • Three-stage countercurrent washing at room temperature (liquid-to-solid ratio 6 mL/g, 45 min) boosted Cl removal to 90.15%, reducing water consumption and energy input for industrial application.
• • Water washing increased BET surface area from 2.71 to 10.11 m²/g and total pore volume from 0.0087 to 0.0412 cm³/g, enhancing the sludge's reactivity for downstream metal recovery.
• • The process reduced metal leaching toxicity, mitigating environmental risks and enabling safer disposal or resource recovery from the treated sludge.