Thermodynamic study of the adsorption of copper (II) onto organic-modified montmorillonite

Abstract

The aim of present study was to evaluate thermodynamics and the equilibrium of adsorption, in aqueous solution, of the Cu²⁺ ion in a montmorillonite organofunctionalized by 3-aminopropyltriethoxysilane. This adsorbent was prepared by the initial intercalation of cetyltrimethylammonium bromide and then functionalization by 3-aminopropyltriethoxysilane. The organofunctionalization occurred on the outer surface of the inorganic matrix. The maximum adsorption capacity of Cu²⁺ by the organofunctionalized sample, predicted by the immobilization density (1.46x10^-3 mol.g^-1), was about 92 mg of Cu²⁺ per gram of clay. The adsorption enthalpy change (ΔH), obtained by calorimetric method was -1.4±0.3 kJ.mol^-1, a very small value to be determined by the application of second law method. Based on the modified Langmuir model, values of 47±10, 41±9 and 48±6 dm³.mol^-1 for the affinity constants were obtained for temperatures of 25, 35 and 45 °C, respectively, which showed equal magnitudes for these physical quantities within the experimental uncertainties.

Keywords: thermodynamics; montmorillonite; adsorption; 3-aminopropyltriethoxysilane; copper