Removal of Hg(II) from an Aqueous Medium by Adsorption onto Natural and Alkyl-Amine Modified Brazilian Bentonite

Abstract

AbstractMercury ion removal from waste-waters has been the subject of extensive research. The aim of the present investigation was to report the incorporation of the n-alkylamine molecules onto a bentonite surface and the capacities of these new chelating moieties on this modified bentonite surface for mercury removal from water. Bentonite collected from the Amazon region, Brazil, was used in an intercalation process with polar n-alkylamine molecules of general formula H3C(CH2)n-NH2 (n = 1 to 4) in 1,2-dichloroethane. The natural and modified bentonite samples were characterized by elemental analysis, Xray diffraction, helium picnometry, mercury porosimetry, and 29Si, 27Al, and 13C nuclear magnetic resonance spectroscopy. Because of the increasing size of the molecules attached to the pendant chains, the metal-adsorption capability of the final chelating materials was measured in each case. The adsorption of Hg(II) on natural and modified bentonites was determined under different conditions. The effects of concentration of Hg(II), contact time, and pH were investigated; batch and dynamic adsorption experiments of Hg(II) were conducted on bentonite samples under various conditions. The ability of these materials to remove Hg(II) from aqueous solution was assessed by means of a series of adsorption isotherms at room temperature and pH 4.0. In order to evaluate the bentonite samples as adsorbents in a dynamic system, a glass column was filled with clay samples (1.0 g each) and fed with 1.8 × 10−4 mol dm−3 Hg(II) at pH 4.0. The energetic effects caused by adsorption of metal cations were determined by means of calorimetric titrations. Thermodynamics indicated the existence of favorable conditions for such Hg(II)-nitrogen interactions.