Uranium (VI) sorption by multiwalled carbon nanotubes from aqueous solution

Sorption of uranium (VI) from aqueous solutions onto Multiwalled Carbon Nanotubes (MWCNTs) has been studied under varying experimental conditions of initial uranium concentration, contact time, pH, and temperature, to assess the kinetic and equilibrium parameters. The optimum pH for sorption of uranium (VI) onto MWCNTs was 5. The kinetic data were fitted with pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The sorption process was well described by pseudo-second-order kinetics. The uranium sorption data were fitted by the Langmuir, Freundlich, and Dubinin-Radushkevich equilibrium models to obtain the characteristic parameters of each model. The Langmuir isotherm was found to best represent the measured sorption data. According to the evaluation using the Langmuir model, the maximum sorption capacity of uranium (VI) ions onto MWCNTs increased with temperature, from 24.9 to 39.1 mg g(-1) when the temperature was increased from 298 to 318 K. The calculated sorption thermodynamic parameters including Delta G degrees, Delta H degrees, and Delta S degrees indicated the spontaneous nature of uranium sorption onto MWCNTs. The results suggest that MWCNTs are suitable materials for preconcentration and solidification of uranium (VI) species from aqueous solutions. (C) 2012 Elsevier B. V. All rights reserved.