Diquite (D) and bentonite (B) mineral samples from the Amazon region, Brazil. were modified by MTTZ derivative (5-mercapto-1-methyltetrazole) using heterogeneous route. These materials were characterized by textural and elemental analysis, transmission electron microscopy (TEM), power X-ray diffraction and C-13 NMR spectroscopy. The chemically modified clay (D-MTTZ and B-MTTZ) samples showed modification of its physical-chemical properties including: specific area 41.4 (B) to 398.5 m(2) g(-1) (B-MTTZ) and 25.0 (D) to 178.8 m(2) g(-1) (D-MTTZ). The adsorption experiments performed under batch process with Th(IV) concentration, pH and contact time as variables. The ability of these materials to remove thorium from aqueous solution was followed by a series of adsorption isotherms adjusted to a Sips equation at room temperature and pH 2.0, with variable concentration of Th(IV). The maximum number of moles adsorbed was determined to be 10.45 x 10(-2) and 12.76 x 10(-2) mmol g(-1) for D-MTTZ and B-MTTZ, respectively. The energetic effects (Delta H-int degrees, Delta(int)G degrees and Delta S-int degrees) caused by thorium cation adsorption were determined through calorimetric titrations. (C) 2009 Published by Elsevier B.V.