Evaluation of Operational Performance in Packed-Bed Column Reactors Using Mill-Scale Derived Fe 3 O 4 Particles for Efficient Arsenic Removal from Aqueous Solutions

This study demonstrates an efficient and sustainable method for synthesizing magnetite (Fe₃O₄) from industrial mill scale waste and its application for long-term arsenic (As) removal in packed-bed column reactors. Magnetite was synthesized via a reverse coprecipitation route optimized by controlling the pH during synthesis. The Fe₃O₄ particles produced at pH 8.3 ± 0.2 exhibited the highest adsorption capacities of 12.68 mg g⁻¹ for As(V) and 10.49 mg g⁻¹ for As(III), with a synthesis yield of 96.7%. Column experiments demonstrated over 99% As(V) removal efficiency using 80 g of Fe₃O₄ at an influent concentration of 1,000 µg L⁻¹ and pH 7.0, maintaining consistent performance through four adsorption–desorption cycles regenerated with 0.2 N NaOH. The reverse coprecipitation method significantly enhanced Fe₃O₄ crystallinity, uniformity, and adsorption efficiency compared with the conventional coprecipitation technique. Furthermore, the synthesized Fe₃O₄ showed high stability, reusability, and scalability, making it suitable for continuous treatment systems. This study provides a practical and eco-friendly approach for recycling industrial mill scale into high-performance magnetite adsorbents, contributing to sustainable waste utilization and environmental protection. The findings highlight the potential of Fe₃O₄-based packed-bed reactors as a cost-effective and scalable solution for removing arsenic from contaminated groundwater.