ADSORPTION OF ETHYLENEDIAMINE (EDA) ON MONTMORILLONITE SATURATED WITH DIFFERENT CATIONS--III. Na-, K- AND Li-MONTMORILLONITE: ION-EXCHANGE, PROTONATION, CO-ORDINATION AND HYDROGEN-BONDING

Abstraet---Ethylenediamine (EDA) is adsorbed from aqueous solution on Na-, Kand Li-montmorillonite as the monoprotonated cation (EDAH +) through an ion-exchange process. On washing with distilled water the second amine function is protonated--probably through dissocmtion of water near the clay surface--and simultaneously formed alkali hydroxide is removed. In air-dried clay films, prepared from unwashed suspensions, EDA is retained mainly through hydrogen-bonding with water co-ordinated to the exchangeable cation. EDA adsorbed from the vapour phase is retained through coordination, either direct or indirect (i.e. through a 'water-bridge'), depending on the hydration properties of the exchangeable cation. Indirect coordination increases the stability of the amino-clay complex against atmospheric humidity and heating in vacuum in the order K + < Na + < Li +. Upon heating co-ordinated EDA is almost completely desorbed, whereas EDAH + and EDAH~ + decompose above 160~ to form NH +.