Synthesis of magnetite/lanthanum hydroxide composite and magnetite/aluminum hydroxide composite for removal of phosphate.

Two magnetic adsorbents, magnetite/aluminum hydroxide composite (MAC) and magnetite/lanthanum hydroxide composite (MLC), were successfully synthesized by a simple one-pot method and their phosphate adsorption process was investigated. The properties of synthesized adsorbents were studied using Fourier transform infrared spectroscopy (FTIR), zeta potential, vibrating sample magnetometry (VSM) and X-ray photoelectron spectroscopy (XPS). The adsorption isotherms, adsorption kinetics and the effects of solution pH and dissolved organic carbon (DOC) on the adsorption of phosphate in aqueous solution by MAC, MLC-2, MLC-10 and LMB were investigated to evaluate the difference in phosphate removal efficiency of the magnetic adsorbents and non-magnetic adsorbent. According to the results of this study, MLC-10 had a higher phosphate adsorption capacity (19.34 mg P g) than LMB (11.55 mg P g), MAC (10.48 mg P g) and MLC-2 (8.89 mg P g). MLC-10 showed a relative higher partition coefficient (PC) (1.74 mg g μM) than other three adsorbents at initial P concentration of 15 mg L. Also, MLC-10 was less pH dependent than MAC and had higher phosphate adsorption capacities under different DOC concentrations (0-72 mg L) than LMB, MAC and MLC-2. Further, MLC-10 had excellent recyclability due to high magnetism. Electrostatic interaction and the inner-sphere surface complexation were the potential phosphate adsorption mechanisms employed by MLC-10. In summary, MLC-10 is a promising adsorbent for phosphate removal from eutrophication water.