Eutrophication has become a worldwide environmental problem and removing phosphorus from water/wastewater before discharge is essential. The purpose of our present study was to develop an efficient material in terms of both phosphate adsorption capacity and magnetic separability. To this end, we first compared the performances of four spinel ferrites, including magnesium, zinc, nickel and copper ferrites. Then we developed a copper ferrite-based novel magnetic adsorbent, by synthesizing 1,6-hexamethylenediamine-functionalized copper ferrite(CuFe2O4) via a single solvothermal synthesis process followed by LaCl3 treatment. The materials were characterized with X-ray diffraction, transmission electron microscope, vibrating sample magnetometer, Fourier transform infrared spectra and N2 adsorption-desorption. The maximum adsorption capacity of our material, calculated from the Langmuir adsorption isotherm model, attained 32.59mg/g with a saturation magnetization of 31.32emu/g. Data of adsorption kinetics were fitted well to the psuedo-second-order model. Effects of solution pH and coexisting anions (Cl-, NO3-, SO42-) on phosphate adsorption were also investigated, showing that our material had good selectivity for phosphate. But OH- competed efficiently with phosphate for adsorption sites. Furthermore, increasing both NaOH concentration and temperature resulted in an enhancement of desorption efficiency. Thus NaOH solution could be used to desorb phosphate adsorbed on the material for reuse, by adopting a high NaOH concentration and/or a high temperature.

To develop a stable and easily separable adsorbent for the efficient removal of phosphate from water, Ce-incorporated zinc ferrites (ZnCexFe2-xO4, x = 0 similar to 0.48) were synthesized and investigated. Results indicated that, though introduction of Ce decreased saturation magnetization, the ferrites were magnetically separable with saturation magnetization exceeded 32.0 emu/g when x <= 0.12. On the other hand, increasing Ce content greatly boosted the adsorptive capacity of phosphate, with Langmuir adsorption maxima increasing from 5.2 mg/g to 41.6 mg/g at 25 degrees C when x increased from 0 to 0.48. However, P/Ce molar ratio was found to be the highest when x = 0.12, enabling the most efficient use of Ce. The adsorption of phosphate was the most favorable within the middle pH range and the increase in both ionic strength and temperature enhanced adsorption. The material showed good affinity for phosphate in the presence of common anions. Experimental results also showed that NaOH or KOH were applicable for the purpose of adsorbent regeneration. In conclusion, Ce-incorporated zinc ferrite with the composition of ZnCe0.12Fe1.88O4 has the potential for the removal of phosphate from water. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Hydrous lanthanum oxide was loaded onto the surface of Fe3O4@SiO2 core/shell magnetic nanoparticles to obtain an easily separable adsorbent (abbreviated as Fe-Si-La) for efficient separation of phosphate from water. Fe-Si-La was characterized with XRF, XRD, TEM, specific surface area and magnetization and their performance for phosphate removal was investigated. The Fe3O4@SiO2 core/shell structure was confirmed and the hydrous lanthanum oxide was successfully loaded onto its surface. The newly developed adsorbent had magnetization of 51.27emu/g. The Langmuir adsorption capacity of phosphate by Fe-Si-La reached 27.8mg/g by loading only 1mmol lanthanum per gram of magnetite. The adsorption was fast; nearly 99% of phosphate could be removed within 10min. The removal of phosphate was favored within the pH range 5.0-9.0. The adsorption on Fe-Si-La was not significantly influenced by ionic strength and by the coexistence of the anions of chloride and nitrate but sulfate, bicarbonate and humic acid showed slightly greater negative effects. Phosphate removal efficiency of higher than 95% was attained for real effluent of a wastewater treatment plant when the dose of adsorbent was >0.2kg/ton. The results showed that adsorbed phosphate could be nearly completely desorbed with NaOH solution for further use. In conclusion, Fe-Si-La is a promising adsorbent for the removal and recovery of phosphate from water.

To develop a phosphate adsorbent in powder form that is easily separated from water, we prepared magnetic spinel zinc ferrite using a facile solvothermal technique. Characterization of zinc ferrite was done by VSM, XRD, TEM, and FTIR measurements. We found that zinc ferrite crystallized as a cubic ZnFe2O4 phase (JCPDS card no. 89-1010). It had a saturation magnetization of 34.95emu/g, which allowed easy separation using a magnet. Phosphate adsorption under different initial phosphate concentrations, solution pH values, ionic strengths, temperatures, contact times, as well as in the presence of competitive ions, was investigated. Data from kinetic experiments fit well the pseudo-second-order model. The maximum adsorption capacity obtained by fitting adsorption isotherm data to the Langmuir model ranged within 5.23–6.28mg/g at different temperatures. Thermodynamic parameters indicate that phosphate adsorption by zinc ferrite is an endothermic and spontaneous process. The amount of phosphate adsorbed increased with decreasing pH and increasing ionic strength. Zinc ferrite showed good selectivity for phosphate. Results suggest that phosphate adsorbed onto the zinc ferrite surface via formation of an inner-sphere complex.