In this work adsorption of uranium on natural, heat and acid treated sepiolite was studied. For acid treatment HCl and H(2)SO(4) were used separately. Heat and acid treatment caused some, changes in sepiolite such as surface area, micropore volume (cm(3)/g) and average pore diameter (A). Different amounts of Mg ions were extracted from the lattice depending on the type of acid. After acid treatment with MCl, the amount of Mg left in the sepiolite changed a little. During H(2)SO(4) treatment the sepiolite structure was progressively transformed into amorphous silica. These heat and acid treatments changed adsorption capacity and mechanism of uranium on sepiolite. Data obtained from the adsorption experiments were applied to Langmuir and Dubinin-Radushkevich (D-R) adsorption isotherms. Using these isotherms different adsorption capacities were found for natural and treated sepiolite samples. The capacity values were 3.58 x 10(-3), 3.14 x 10(-3), 2.78 x 10(-3) and 1.55 x 10(-3) mol/g for HCl treated, heat treated, natural and H(2)SO(4) treated sepiolite samples, respectively. In order to evaluate the adsorption mechanism adsorption energies were calculated by the D-R isotherm. According to the adsorption energy values uranium fixed to the natural and heat treated sepiolite surface with ion exchange (12.75 and 12.12 kJ/mol, respectively). Simple physical attractions were the driving force for adsorption on HCl and H(2)SO(4) treated ones (6.62 and 6.87 kJ/mol, respectively). (C) 2010 Elsevier Ltd. All rights reserved.