Adsorption kinetic, thermodynamic and desorption studies of Th(IV) on oxidized multi-wall carbon nanotubes

The adsorption kinetics of Th(IV) on oxidized multi-wall carbon nanotubes (MWCNTs) was investigated at initial Th(IV) concentrations 32.32 and 64.64 mu mol/L. The kinetic process was described by a pseudo-second-order rate model very well. The adsorption thermodynamics of Th(IV) on oxidized MWCNTs was carried out at 293 +/- 2, 303 +/- 2, and 323 +/- 2 K, respectively, and the thermodynamic parameters, such as equilibrium constant (K-0), standard free energy changes (Delta G degrees), standard enthalpy change (Delta G degrees) and standard entropy change (Delta H degrees), were obtained. The Langmuir model described the data better than the Freundlich isotherm model. Desorption studies indicated that Th(IV) adsorption was reversible and Th(IV) ions could be desorbed from the surface of carbon nanotubes by adjusting the pH values. Oxidized MWCNTs may be a promising candidate for the preconcentration and solidification of Th(IV), or its analogue actinides from large volumes. (C) 2007 Elsevier B.V. All rights reserved.