Activated silica get was directly modified with a cyclic molecule, ethyleneimine, yielding a surface with various nitrogen basic centers, equivalent to Sil-O(CH2CH2NH)(n)CH2CH2NH2. Infrared spectroscopy, C-13 NMR, thermal, and elemental analyses confirmed the covalent attachment of the organic species onto the silica matrix. The purpose of this paper is to describe the interaction involving the grafted species on silica surface with the divalent heavy cations, Pb(II), Cd(II), and Hg(II), from aqueous solutions at room temperature, The process of metal extraction was followed by the batch method and the order of the maximum extraction capacities found was: 1.27 +/- 0.04, 1.02 +/- 0.02, and 0.98 +/- 0.01 mmol g(-1) for Pb(II), Cd(II), and Hg(II) chlorides, respectively. These interactions were followed by calorimetric titration, The enthalpies of these processes are: -3.05 +/- 0.02, -1.09 +/- 0.01, and -9.88 +/- 0.03 kJ mol(-1) for Pb(II), Cd(II), and Hg(II), respectively. The standard molar Gibbs free energies are in agreement with the spontaneity of the proposed reactions between cation and basic center. (C) 2005 Elsevier B.V. All rights reserved.