Monodisperse magnetic hydroxyapatite/Fe3O4 microspheres for removal of lead(II) from aqueous solution

Monodisperse magnetic hydroxyapatite (HAp)/Fe3O4 microspheres were successfully synthesized and explored for the removal of lead(II) from aqueous solution. The mechanism of Pb2+ uptake was characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. The sorption capacity toward Pb2+ reached 440 mg/g at pH 3.0 and equilibrium was achieved within 1 h. The experimental data followed the Langmuir isotherm model (R2 = 0.9969) and the kinetic results accorded with the pseudo-second-order model (R2 = 0.9970). The sorption of Pb2+ on the surfaces of HAp/Fe3O4 and the following ion exchange are the primary mechanism at pH 3.0-6.0. The dissolution-precipitation mechanism response to the removal of Pb2+ when pH varied from 3.0 to 2.0. The Pb2+-loaded magnetic HAp/Fe3O4 could be separated conveniently.