As(V) adsorption by a novel core-shell magnetic nanoparticles prepared with Iron-containing water treatment residuals

A novel core-shell magnetic nanoparticle was synthesized through heterogeneous nucleation technique and utilized to remove As(V) from water. Both the magnetic core and the coating material, amorphous FeOOH shell, were prepared with iron-containing water treatment residuals (WTRs), also called iron sludge. The bare magnetic nanoparticles (MNPs) and coated magnetic nanoparticles (c-MNPs) were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Brunauer-Emmett -Teller analysis (BET), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FTIR). The c-MNPs, mainly consisting of maghemite (γ-Fe₂O₃) as the magnetic core and amorphous FeOOH as the coating material, could be easily separated from water through a hand-held magnet, the saturation magnetization of which is 36.4 emu/g. Freundlich adsorption isotherm model could better described the As(V) adsorption behavior of c-MNPs than Langmuir model, and kinetic data could be described well by the pseudo-second order model. The maximum As(V) adsorption capacity of c-MNPs (26.05 mg/g) was more than twice that of MNPs (12.74 mg/g). At 25 °C, 0.2 g/L of the c-MNPs could reduce the As(V) from 400 μg/L to below the maximum contaminant level (MCL) of 10 μg/L over a broad pH ranging from 4 to 8. The c-MNPs still exhibited effective adsorption in the presence of co-existing anions including nitrate, chloride, carbonate, and sulfate, whereas, silicate and phosphate had a negative influence on the As(V) adsorption. Throughout five consecutive cycles, the adsorbents could still maintain high As(V) adsorption capacity.