An attapulgite (ATPG) clay sample has been chemically modified with silylating agents N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide. The resulting matrices (ATPG(3TPT) and ATPG(NPTM)) have been characterized by elemental analysis, X-ray diffractometry, carbon nuclear magnetic resonance in the solid-state, and scanning electron microscopy. The natural and modified clay samples have been tested as potential adsorbents for the removal of uranyl(II) from aqueous solution at pH 2.0 and 298 +/- 1K. The maximum number of moles adsorbed was determined to be 5.55, 14.86, and 18.99 x 10(-2) mmol g(-1) for ATPG, ATPG3TPT, and ATPGNPTM, respectively. From calorimetric determinations the quantitative thermal effects for UO(2)(2+)/center interactions gave exothermic enthalpy (-6.90 to -7.88 kJ mol(-1)), negative Gibbs free energy (-22.34 to -24.56 kJ mol(-1)), and positive entropy (51.80-56.00 1 K(-1) mol(-1)). These thermodynamic data confirmed the energetically favorable condition of such interaction at the solid/liquid for all systems. (C) 2009 Published by Elsevier B.V. on behalf of The institution of Chemical Engineers.