Magnetic Fe3O4 @ silica-xanthan gum composites for aqueous removal and recovery of Pb2+

A magnetic Fe3O4 @ silica-xanthan gum composite was easily fabricated as a hybrid adsorbent for the removal and recovery of aqueous Pb2+ heavy metal. The natural polymer xanthan gum (XG) was fixed on the surface of the magnetic Fe3O4 microspheres through a sol-gel process. The condensation of XG molecule provided active sites for the selective adsorption of Pb2+ ions from the aqueous solution, and because the composite is magnetically switchable, the process of solid-liquid separation was convenient. Scanning electronic microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, thermogravimetry, and BET surface area determination were utilized for the characterization of the composites. The factors affecting Pb2+ adsorption in a batch mode were studied including the contact time (30-150 min), the pH of the media (2-10), the adsorbent dosage (0.01-0.2g/20 mL), and the temperature (303-320 K). The Pb2+ adsorption followed pseudo-second-order kinetics, and the maximum Pb2+ sorption capacity was 21.32 mg g(-1) at 293 K, pH = 6, according to the Langmuir isotherm. The thermodynamic parameters, including the equilibrium constant (K-0 = 9.848), the standard free energy change (Delta G(0) = -5.774 kJ mol(-1)), the standard enthalpy change(Delta H-0 = 6.133 kJ mol(-1)), and the standard entropy change (Delta S-0= 39.21 J mol(-1)K(-1)) were discussed. The targeted Pb2+ could be recovered efficiently using 0.05 mol L-1 HCl. Finally, the Fe3O4 @ silica-XG composites were attmepted for removal of Pb2+ from battery industry wastewater. (C) 2013 Elsevier B.V. All rights reserved.