Co‐Pyrolysis of Coking Sludge and Cold‐Rolling Oily Sludge Toward Functional Biochar for Cr(VI) Removal: Performance and Mechanistic Insights

Abstract Industrial Cr(VI) effluents pose persistent environmental threats due to their toxicity and non‐biodegradability. This study pioneers a novel functional sludge‐derived biochar (SC@BC) synthesized via co‐pyrolysis of coking sludge (CS, carbon source) and cold‐rolling oily sludge (CROS, iron source) for enhanced Cr(VI) removal. Under optimized conditions (pyrolysis temperature: 800 °C, CS:CROS mass ratio = 1:1), SC@BC demonstrated a maximum Cr(VI) adsorption capacity of 161.13 mg/g. Kinetic analysis revealed that the adsorption process followed a pseudo‐first‐order model, governed by synergistic mechanisms of external diffusion and surface reactions. The removal mechanism involved electrostatic attraction, hydrogen bond, surface complexation, redox reactions, and precipitation, where Fe(II) acted as an electron donor to reduce Cr(VI) to less toxic Cr(III). Subsequent co‐precipitation of Cr(III) with Fe(III) enhanced pollutant immobilization. ICP‐MS analysis confirmed compliance of heavy metal leaching concentrations with GB 13456‐2012 standards, validating environmental safety. This work provides a sustainable “waste‐treats‐waste” strategy for dual‐sludge valorization and high‐efficiency Cr(VI) remediation. Future research should assess SC@BC's scalability for industrial effluents and efficacy in multi‐contaminant systems.