[One-step Preparation of Lanthanum-Magnesium Ferrite and Its Phosphate Adsorption Capacity in Aqueous Solutions]

Due to the shortage of phosphate and the eutrophication caused by phosphorus pollution, it is urgent to recover phosphate from wastewater. Given their high adsorption capacity and convenient separation from water to which a magnetic field is applied, ferrite composites have received increasing attention for phosphate recovery. In this study, Spinel La@MgFe₂O₄ was prepared using a one-step co-precipitation method. La³⁺ loading on grain boundary defects of MgFe₂O₄, and phosphorus absorption capacity were examined using X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The structure of La@MgFe₂O₄ involved La³⁺ loading on grain boundary defects of MgFe₂O₄ in the form of La(OH)₃. The addition of La changed the crystallinity and morphology of MgFe₂O₄, which greatly improved the capacity of MgFe₂O₄ for phosphorus adsorption. Saturation magnetization remained at 14 emu·g^-1, which was easily separated from water using an external magnetic field. The maximum adsorption capacity was 143.156 mg·g^-1 at pH 6 and 10℃, which was comparable to that achieved at 25℃. Kinetic observations showed that a low phosphorus concentration (10 mg·L^-1) could result in extremely low phosphorus adsorption by La@MgFe₂O₄ after 30 min. The adsorption mechanism shows that phosphorus is removed through ligand exchange and the formation of inner spherical complexes. La@MgFe₂O₄ has highly selective adsorption with respect to phosphate, and the adsorbent can be reused many times after desorption. Based on addition of 1 g·L^-1 of La@MgFe₂O₄ in the treatment of low temperature municipal wastewater in Northern China, phosphate concentrations could be reduced to less than 0.5 mg·L^-1 an hour, offering a promising means of phosphate adsorption even in cold regions.