Mill Scale–Derived Magnetite Particles: Effective Adsorbent for the Removal of Phosphate in Aqueous Solutions

Abstract

Mill scale, an iron waste, was used to synthesize magnetite particles for the adsorption of phosphate from an aqueous solution. Several techniques were used to characterize the adsorbents. Mill scale–derived magnetite particles exhibited a strong uptake affinity to phosphate in a wide pH range of 3–7, with the maximum adsorptive removal of 100% at an adsorbent concentration of 1 g/L and pH 3–5. The Langmuir isotherm model well described the equilibrium data, exhibiting maximum adsorption capacities for phosphate up to 4.95 and 8.79 mg/g at 298 and 308 K, respectively. Kinetic data correlated well with the pseudo-second-order kinetic model, indicating that chemisorption is involved in the adsorption process. The phosphate adsorption was highly pH-dependent, and the presence of Cl−, SO42−, and CO32− ions had no effect on phosphate removal. X-ray photoelectron spectroscopy (XPS) results revealed that phosphate was bonded onto the surface of magnetite predominantly through bidentate complexation. Desorption was performed on mill scale–derived magnetite to check recyclability. Five successive adsorption/regeneration cycles were successfully applied with a slight decrease in the adsorbent adsorption capacity.