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Abstract
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This study presents a sustainable and scalable method for converting waste sheep wool into high-performance activated carbon for the removal of hexavalent chromium [Cr(VI)] from aqueous solutions. Both chemical activations using NaOH and physical activation using steam were systematically evaluated, with steam activation at 900 °C for 3 hours producing the optimal material. The resulting activated carbon exhibited a high specific surface area (1807 m²/g), substantial pore volume (1.002 cm³/g), and a well-developed micro-mesoporous structure. A custom-designed rotary furnace was engineered to enable uniform heat distribution, controlled steam flow, and semi-industrial processing capacity (>7 L wool per batch), addressing scale-up limitations commonly reported for biomass-derived carbons. The optimized carbon demonstrated rapid and efficient Cr(VI) removal, achieving 99% removal from a 400 mg/L solution within 45 minutes. Characterization by BET, SEM, XRD, Raman, ICP-OES, and ASTM standard tests confirmed its structural, chemical, and mechanical suitability for adsorption applications. Adsorption equilibrium was best described by the Freundlich isotherm (R² = 0.976), although the Langmuir model provided a maximum monolayer adsorption capacity of 147 mg/g. Kinetic analysis revealed a strong fit to the pseudo-second-order model (R² = 0.999), indicating chemisorption involving electrostatic attraction, redox reduction of Cr(VI) to Cr(III), and complexation with surface functional groups. Overall, the results demonstrate that wool waste can be effectively valorized into a high-efficiency, low-cost, and scalable adsorbent suitable for industrial Cr(VI) remediation, contributing to circular economy strategies and sustainable wastewater treatment technologies.
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