Phosphate removal using zinc ferrite synthesized through a facile solvothermal technique

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 34.95 emu/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 5.23–6.28 mg/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.