Phosphate compounds are widely used in agriculture and industry and its release leads to significant eutrophication and water quality problems such as fish death, promote parasite infection, amphibian disease, growth of harmful algal blooms, as well as depletion of dissolved oxygen [1, 2]. Various biological, physical and chemical methods have been developed to remove phosphate from wastewaters. Among the proposed methods, adsorption technology is regarded as one of the competitive methods because of high efficiency at low phosphate concentrations, feasibility and simplicity of operation [2, 3]. The removal efficiency may be enhanced by using nano-sized powder as an adsorbent. However, nano-adsorbent has intrinsic drawback due to the difficulties of sedimentation and separation in such a slurry type system. Hence, immobilizing the nanoadsorbents on the magnetic matrix may enable efficient usage of the nanoparticles due to their high surface area and easy separation under external magnetic fields [4]. In this study, a novel adsorbent, nanocomposite of Fe3O4-La2O (CO3)2, has been prepared by the ultrasound-assisted chemical precipitation method. Products were characterized by XRD, TEM, and FT-IR. The phosphate adsorption was determined by measurement of the aqueous concentration of phosphate using UV–vis spectroscopy. The effects of amount of sorbent, initial concentration of phosphate in solution, temperature and pH on the efficiency of phosphate removal were investigated. The adsorption isotherms and kinetics were evaluated too. In addition, the mechanism and the relationship between the adsorption amount and the pH of phosphate solution were investigated. In overall, the synthesized nanocomposite showed an exceptional removal of phosphate ions under obtaining optimum conditions.

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