In this study, the original tourmaline and beryl mineral samples have been collected from a Brazilian pegmatite. The objective of this study was to examine the adsorption behavior of uranyl from aqueous solution on Brazilian cyclosilicate samples. The cyclosilicate samples were characterized by elemental analysis, X-ray diffraction, and nitrogen adsorption-desorption. The ability of these minerals to remove the U(VI) from aqueous solution was followed by a series of adsorption isotherms, using a batchwise process. The adsorption maximum was determined to be 2.95 and 2.60 x 10(-4)mol g(-1) for beryl and tourmaline mineral samples, respectively. The energetic effects caused by radionuclide cation adsorption were determined through calorimetric titrations. Thermodynamics indicated the existence of favorable conditions for such U(VI)-OH interactions. (C) 2011 Published by Elsevier B.V.