In situ grown of nano-hydroxyapatite on magnetic CaAl-layered double hydroxides and its application in uranium removal

This paper report on the efficient removal of uranium ions from aqueous solution with a novel magnetic composite adsorbent, calcined magnetic layered double hydroxide/hydroxyapatite (CMLH). This adsorbent was obtained via in situ grown of nano-hydroxyapatite on magnetic CaAl-layered double hydroxides and followed with calcining. The morphology and microstructure of the as-prepared adsorbents were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The influences of conditions for uranium removal, including dosage of LDHs, pH of aqueous solution, and temperature on anion-exchange have been investigated, respectively. The thermodynamic parameters including Gibbs free energy (Delta G(0)), standard enthalpy change (Delta H-0) and standard entropy change (Delta S-0) for the process were calculated using the Langmuir constants. It was found from kinetics test that the pseudo-second order kinetics model could be used to well describe the uptake process. Furthermore, the CMLH could be regenerated through the desorption of the uranium using 0.5 M NaHCO3 solution and could be reused to adsorb after calcination. (C) 2012 Elsevier B.V. All rights reserved.