Superior adsorption of phosphate by ferrihydrite-coated and lanthanum-decorated magnetite

Present study reports the successful development of a novel lanthanum (La)-based magnetic adsorbent and its use for phosphate removal from water. For its synthesis, natural magnetite (Mag), Fe 3 O 4 , was subjected to partial dissolution in HCl solution and the obtained suspension was mixed with an alkaline solution for in-situ synthesis of ferrihydrite (Fh)-coated Mag (Mag@Fh). Mag@Fh was then decorated with La (hydr)oxides followed by calcination to produce Fh-coated and La-decorated Mag (Mag@Fh-La). Obtained Mag@Fh-La represented high phosphate adsorption capacity (44.8 mg P/g at 15.7% La in its structure) and La usage efficiency. Moreover, Mag@Fh-La retained its high adsorption capacity (>35.0 mg P/g) over a wide range of equilibrium solution pH (3.2–10.7). The combination of FTIR , XPS analysis and adsorption experiments revealed that ligand exchange and electrostatic attraction were the main mechanisms that jointly facilitated the adsorption of phosphate. Adsorption-desorption cycle studies confirmed the well-retained adsorption efficiency of regenerated Mag@Fh-La for repeated applications. Final experiments with real domestic wastewater (initial phosphate concentration of 1.7 mg/L) revealed that 0.2 g/L Mag@Fh-La efficiently reduced the phosphate concentration to below 0.02 mg/L. Overall, this work clearly highlights that the synthesized novel adsorbent has promising applications in phosphate removal from real wastewater .