Adsorption of Ethylenediamine (Eda) on Montmorillonite Saturated with Different Cations—IV: Al-, Ca- and Mg-Montmorillonite: Protonation, Ion-Exchange, Co-Ordination and Hydrogen-Bonding

Abstract

Ethylenediamine (EDA) adsorbed from aqueous solution or vapor phase on Al-, Ca- and Mg-montmorillonite was retained to a more or less large extent in protonated form. The NH⁺₃:NH₂ ratio decreased with the polarizing power of the mineral exchange cation (Al < Mg < Ca) and with increasing amounts of amine fixed. Excess EDA was adsorbed through hydrogen-bonding with protonated species, and partially through co-ordination in vapor treated samples. Co-ordination to the exchangeable cation seemed to be favored in the order Al > Mg > Ca, and the complexes were stable up to 200°C. Heating lowered the NH⁺₃:NH₂ ratio, indicating some deprotonation process caused probably by the competition for protons between EDA and hydrolysed exchange cations. This competition might also account for the rather low quantities of NH⁺₄ produced near 200°C.