Article pubs.acs.org/jced
Magnetic Strontium Hydroxyapatite Microspheres for the Efficient Removal of Pb(II) from Acidic Solutions Fu-Qiang Zhuang,† Rui-Qin Tan,*,† Wen-Feng Shen,‡ Xian-Peng Zhang,‡ Wei Xu,‡ and Wei-Jie Song‡ †
Faculty of Information Science and Engineering, Ningbo University, Ningbo 315211, PR China Ningbo Institute of Material Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, PR China
‡
ABSTRACT: Magnetic strontium hydroxyapatite (Fe3O4−SiO2−SrHAp) monodispersed microspheres were successfully synthesized by a hydrothermal method and investigated as a sorbent for the removal of Pb(II) from acidic aqueous solutions. The maximum immobilization capacity was 345 mg·g−1 for Pb(II) at pH 3.0, and equilibrium was achieved within 120 min. The experimental data followed the Langmuir isotherm model (R2 = 0.9987), and the kinetic results accorded with the pseudo-second-order model (R2 = 0.9982). The Pb(II)-loaded magnetic sorbent was easily separated from aqueous solutions using a permanent magnet.
1. INTRODUCTION Heavy metal ion pollution in the environment has become a critical issue worldwide because of population growth and extensive industrial production.1,2 In an effort to combat water pollution, many materials have been developed including carbon nanotubes,3 Pb(II)-imprinted silica,4 and active zeolites.5 However, their applications are restricted by many factors such as economic benefit, removal efficiency, and operational techniques. Hydroxyapatite (CaHAp), a bioactive and biocompatible ceramic, is an eco-friendly material that can be used for the disposal of heavy metal ions because of its high capacity, selectivity, and moderate solubility.6−9 Strontium hydroxyapatite (SrHAp) is isomorphous to CaHAp and also plays an important role in the removal of heavy metal ions.10 Because the radius of Sr(II) (118 pm) is larger than that of Ca(II) (99 pm) and their electronegativities are similar, SrHAp is expected to have superior exchange properties toward divalent cations by comparison with CaHAp.11,12 In our previous work, we reported the synthesis of SrHAp nanorods via a hydrothermal method.13 The immobilization capacity toward Pb(II) by the SrHAp nanorods reached 1482 mg·g−1 at pH 2.5. However, its separation after the treatment process tends to be expensive because of the time required, filtration, and manpower. Recently, much attention has been devoted to magnetic nanoparticles in the field of environmental protection and remediation because of their excellent magnetic property, their possible surface modification, their high surface-area-to-volume ratio, and environmental security.14−16 Yi et al. reported the synthesis of a new class of core−shell structure designated Fe3O4−SiO2−1,3-calixcrown microspheres, which exhibit specific recognition and a high removal efficiency toward Pb(II) at low concentrations.17 Deng et al. synthesized magnetic graphene oxide and used it as an adsorbent for the removal of Cd(II). The maximum sorption capacity in ultrapure water toward Cd(II) was 91.29 mg·g−1.18 However, the removal efficiency of these materials toward heavy metal ions decreased © 2014 American Chemical Society
sharply at pH
