Sorption studies of uranium and thorium on activated carbon prepared from olive stones: Kinetic and thermodynamic aspects

Activated carbon prepared by the chemical activation of olive stone was examined for the sorption of uranium and thorium from aqueous solutions. Precursor/activating agent (ZnCl2) ratio (1:2) and 500 °C carbonization temperature were used for the preparation of the sorbent. The total sorption capacities were found to be 0.171 and 0.087 mmol g−1 for uranium and thorium, respectively. The sorption of uranium and thorium was studied as a function of shaking time, pH, initial metal ion concentration, temperature and adsorbent concentration in a batch system. The sorption followed pseudo-second-order kinetics. ΔH° and ΔS° values for thorium and uranium sorption were calculated from the slope and intercept of plots of ln Kd versus 1/T. The positive values of ΔH° indicate the endothermic nature of the process for both metals and decrease in the value of ΔG° with rise in temperature show that the sorption is more favorable at high temperature.