Adsorption of Ethylenediamine (EDA) on Montmorillonite Saturated with Different Cations—II. Hydrogen- and Ethylenediammonium-Montmorillonite: Protonation and Hydrogen Bonding

Abstract

Abstract--The form under which ethylenediamine (EDA) is adsorbed from aqueous solution by hydrogen-and ethylenediammonium-montmorillonite was studied as a function of the amount of amine present in the system. EDA added to the acid clay in quantities lower than or equal to the cation exchange capacity 9 " 2+ (C.E.C.) was exclusively adsorbed as ethylenedlammonmm (EDAH2) ion. On further addition of diamine the pH of the suspension rose to alkaline values and the monoprotonated species (EDAH § was the main charge balancing cation. Evaporating at room temperature "EDA-H-montmorillonite-H20" or "EDA-EDAH2-montmorillonite-H20" systems containing 300 me EDA/100 g clay did not cause loss of nitrogen, but degassing under high vacuum (10 -~ rnm Hg) did. Nevertheless, excess EDA molecules with respect to the C.E.C. were retained on the clay surface, at the expense of water molecules, through strong asymmetrical hydrogen bonds between their NH2 groups and the NH3 + groups of EDAH + ions. On heating up to 160~ under vacuum the nitrogen content decreased further, but still remained at a level significantly higher than the C.E.C. value, all NH3 + groups remaining involved in strong hydrogen bonding. It is suggested that a "condensation" process takes place, implying evolution of EDA molecules and giving rise to "polymeric" associations between protonated and unprotonated diamine.Washing the clay suspensions with distilled water did not completely remove excess EDA either, as a consequence of the equilibrium existing between the ionic species in solution (EDAH2 ~+ and EDAH § and on the clay surface. It seems that these species were preferentially adsorbed as "trimeric" associations in which two out of four NH3 § groups are hydrogen bonded to NH2 groups.After heating at 200~ nitrogen retained on the clay surface was mainly in the form of NH4+ ions. Ammonium formation was enhanced by the presence of excess EDA and was considerably faster than in montmorillonite systems containing EDA coordinated to Cu ~+ ions.

Molecular Structure Effects on Diffusion of Cations in Clays

“…In contrast, the electrochemical experiments shown here suggest that addition of the 6 carbons in Co(en)33+, results in a substantially decreased observable electrostatic mechanism relative to Co(NH3)63+. This observation is consistent with that made by Knudsen and McAtee (1973) who suggested that Co(en)33+/Na § exchange with clay was not solely electrostatic in nature, The non-electrostatic retention of the complexes may occur via H-bonding (Cloos and Lauro 1972) or via substitution of ligands by the clay surface as is observed for Cu(en)32 § (Burba and McAtee 1977). Surface substitution for axial ligands results in an increase of the crystal field stabilization energy for Cu(en)32 § (Velghe et al 1977;Maes et al 1980).…”

Adsorption of Ethylenediamine (EDA) on Montmorillonite Saturated with Different Cations—III. Na-, K- and Li-Montmorillonite: Ion-Exchange, Protonation, Co-Ordination and Hydrogen-Bonding

“…They showed the same features and the same modifications on heating in vacuum ( Fig. 1) as those recorded on EDA-H-montmorillonite complexes (Cloos and Laura, 1972) with amine contents lower than or equal to the CEC of the clay.…”

“…Similarly, the disappearance of the broad absorption centered on 1500 cm-1 suggests that some N-H vibration is involved here, possibly 6NH~-sym. But the corresponding strong and broad stretching band, which is expected near 3200 cm-1 (Cloos and Laura, 1972) is not apparent. Therefore, it can be concluded that EDA is retained mainly in the unprotonated form.…”

“…1). In aqueous medium (Cloos and Laura, 1972) a pH lower than 7 would be required to allow the predominance of EDAH~ + with respect to EDAH +. This provides further evidence for the surface acidity, which has been attributed (Fripiat et al, 1965;Fripiat, 1968;Mortland, 1968;Mortland and Raman, 1968) to a higher than usual degree of dissociation of water subject to the polarizing fields of the exchangeable cations and the mineral surface.…”

“…The interactions between exchangeable copper (II), hydrogen and ethylenediammonium ions on a montmorillonite surface and ethylenediamine (EDA) adsorbed from aqueous solution have been described previously (Laura and Cloos, 1970;Cloos and Laura, 1972). The present study deals with the adsorption of EDA on Na-, K-and Li-montmorillonite.…”