Performance of natural and modified smectite - kinetic and thermodynamics involving arsenic (V) adsorption (Desempenho de esmectita natural e modificada - cinética e termodinâmica envolvendo adsorção de arsênio (V))

A natural smectite sample has been modified by organofunctionalization process using synthetic route involved the reaction of 2-mercaptopyrimidine with 3-chloropropyltriethoxysilane. The resulting material (SMPY) was characterized by SEM, FTIR, textural analysis and 29Si MAS-NMR. The ability of this material to removed As (V) from aqueous solution was followed by series of adsorption isotherms adjusted to the Langmuir equation at room temperature and pH 2.0. The kinetic parameters analyzed by Lagergren and Elovich models gave a good fit for a pseudo-second order reaction with k2 in the 4.9 to 14.0 mmol -1 min-1 range for SMPY. The adsorption process was exothermic (DintH = -4.09 to -5.79 kJ.mol-1) accompanied by increase in entropy (DintS = 41.29 to 61.80 JK -1.mol-1) and Gibbs energy (DintG = -22.34 to -24.19 kJmol-1). The energetic effect caused by arsenic 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.