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 (ZnCl(2)) ratio (1:2) and 500 degrees 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. Delta H degrees and Delta S degrees values for thorium and uranium sorption were calculated from the slope and intercept of plots of In K(d) versus 1/T. The positive values of Delta H degrees indicate the endothermic nature of the process for both metals and decrease in the value of Delta G degrees with rise in temperature show that the sorption is more favorable at high temperature. (C) 2009 Elsevier B.V. All rights reserved.