Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)A synthetic Na-magadiite sample has been modified by organofunctionalization process using synthetic route involved the reaction of 2-mercaptopyrimidine with 3-chloropropyltriethoxysilane. The ability of these materials to remove As(V) from aqueous solution was followed by a series of adsorption isotherms adjusted to the Langmuir equation at room temperature and pH 2.0. The kinetic parameters analyzed by the Lagergren and Elovich models gave a good fit for a pseudo-second-order reaction with k(2) in the 4.9-14.0 mmol (1) min (1) range for M(MPY). The adsorption process was exothermic (Delta(int)H = -4.09 to -5.79 kJ mol (1)) accompanied by increase in entropy (Delta(int)S = 41.29-61.80 J K (1) mol (1)) and Gibbs energy (Delta(int)G = -22.34 to -24.19 kJ mol (1)). The energetic effect caused by arsenic(V) 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) 2009 Published by Elsevier B.V.2563702709Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)