The synthetic Kenyaite sample was used for organofunctionalization process with N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide. The resulted materials were submitted to process of adsorption with arsenic solution at pH 2.0 and 298 +/- 1 K. The adsorption isotherms were adjusted using a modified Langmuir equation with regression non-linear; the net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation. The adsorption process was exothermic (Delta H-int = -4.08 to -5.94 kJ mol(-1)) accompanied by increase in entropy (Delta S-int = 41.29-62.09 J K-1 mol(-1))and Gibbs energy (Delta(int)G = -22.33 to -24.45 kJ mol(-1)). The energetic effect caused by metal cation adsorption was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic Values and the equilibrium constant. (C) 2008 Published by Elsevier B.V.