Adsorption of zinc and copper ions on natural and ethylenediamine modified montmorillonite

Abstract

In this study, adsorption of the zinc and copper ions on montmorillonite (MMT) was investigated. In all experiments performed at pH 6.4 to 4.8, the Langmuir-Freundlich isotherm was found to best fit adsorption data that confirms a monolayer formation of the metals. The maximum amounts of the adsorbed metals did not exceed a cation exchange capacity (CEC) of MMT. UV-VIS diffuse reflectance spectrometry reveals no complexes between Zn2+ or Cu2+ and MMT and thus the metal uptake took part only by ion exchange. X-ray diffraction (XRD) patterns indicated an intercalation of the metal ions into the montmorillonite interlayer. In addition, using thermogravimetry and infrared spectrometry it was found the intercalated metals create aqua complexes [Zn(H2O)6]2+ and [Cu(H2O)6]2+. In order to increase the adsorbed amounts of Zn2+ and Cu2+, MMT was previously intercalated with ethylenediamine (EDA-MMT). EDA caused an increase of the adsorbed copper ions about 28 % due to the formation [Cu(EDA)2]2+ in the interlayer as was confirmed by the infrared spectrometry. Adsorbed amounts of the zinc ions on EDA-MMT was 3-4 folds higher than CEC but no complex with EDA was observed. This effect was explained by expansion of a space between the montmorillonite layers, which facilitates the intercalation of the zinc ions and nitrate compensating the excessive positive charge.