Kinetics, isotherm and thermodynamics for uranium and thorium ions adsorption from aqueous solutions by crystalline tin oxide nanoparticles

This study focused mainly on the synthesis of nano tin oxide as an adsorbent via homogeneous precipitation using urea as a reagent to control the pH and to obtain a pure and dense hydrous tin oxide precipitate. XRD and BET surface area showed that prepared tin oxide was crystallized in cassiterite phase and had a BET surface area of 27.5 m2/g. The synthesized adsorbent was then used for the removal of uranium (VI) and thorium from aqueous solution and factors such as adsorption kinetics, isotherm models and the influence of initial pH of the solution on the adsorption were investigated in a batch system. The kinetic data corresponds well to the pseudo second order equation. In order to specify the type of adsorption reaction, thermodynamic parameters such as the standard enthalpy, entropy, and Gibbs free energy were also determined. ΔH° and ΔS° values for thorium and uranium sorption were calculated from the slope and intercept of plots of lnKd versus 1/T. The evaluated ΔG° and ΔH° indicate the spontaneous and endothermic nature of the reactions. The adsorption data for uranium (VI) were well fitted by the Freundlich isotherm.