Recovery and utilization of phosphorus in wastewater by magnetic Fe3O4/Zn-Al-Fe-La layered double hydroxides(LDHs)

Abstract Layered double hydroxides (LDHs) are the promising minerals which can adsorb phosphates, moreover, phosphorus-containing LDHs can be used for fertilizers. In this study, we tested the ability of magnetic Fe 3 O 4 /Zn-Al-Fe-La -LDH to remove and recover phosphate from simulated sewage. Results demonstrated that a magnetic Fe 3 O 4 /Zn-Al-Fe-La-LDH dose of 1.2 g/l could achieve a maximum adsorption capacity of 169.5 mg/g under an initial phosphate concentration of 200 mg/L, an equilibrium contact time of 24 h and a pH of 4. The adsorption kinetics of phosphate onto the magnetic Fe 3 O 4 /Zn-Al-Fe-La-LDH were well governed by the pseudo-second-order kinetic model, and the adsorption data fit well to the Langmuir isotherms. After four adsorption-desorption cycles, the LDH still had an adsorption capacity of 31 mg/g, demonstrating its reusability. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis indicated that ion exchange occurred between phosphate and the interlayer anions, and that phosphate was inserted into the double structure of the adsorbent. ICP-OES analysis showed that the LDH was stable and did not release the metal ions into water. The phosphorus-adsorbed LDH (P-LDH) has the potential to be used as a slow-release fertilizer to increase the growth of the soybeans Glycine max . The absorption of the metal into the soybeans was also reduced, which proved that the application of this type of LDH is non-toxic to plants.