THE REACTION OF AMMONIA WITH VERMICUL ITE AND HYDROBIOT ITE

ABSTRACT: The reaction of ammonia with Mg-saturated vermiculite and hydrobiotite was studied by chemical nalysis, X-ray diffraction, and differential thermal analysis, and the hydrobiotite also by infrared spectroscopy. The experimental evidence indicates that ammonia isadsorbed mainly as the ammonium ion, formed partly by reaction with inter-layer water and partly by reaction with protons dissociated from octahedral l yer hydroxyl groups, giving a single sheet of ions and molecules with irregular interlayer spacing. With large flakes (0"5-1.0 ram) the adsorbed ammonia is strongly retained on heating or on rehydration with water vapour: smaller flakes lose ammonia more readily. Ammonia uptake is related quantitatively to cation exchange capacity with two vermiculites and three hydrobiotites, and to the water content prior to adsorption. Na-saturated vermiculite adsorbs asimilar amount of ammonia to the Mg form, but it is mostly desorbed on rehydration. Cu-saturated vermiculite displays intermediate b haviour, with much of the ammonia initially present as a Cu-ammine which slowly reacts to give more ammonium ion. Since the review by Mortland (1966), studies of the reaction between ammonia nd clay minerals have been reported by Mortland & Raman (1968) and by Ahlrichs et al. (1972). Ammonia is adsorbed by coordination to exchange cations and by formation of NH +4 with interlayer water. Both are hydrogen-bonded to less strongly held ammonia molecules that can be removed on evacuation (Russell, 1965; Ahlrichs et aL, 1972). However, little attention has been given to the reaction of ammonia with protons dissoci-ated from lattice hydroxyls, or to the quantitative relationships between ammonia uptake, cation exchange capacity, initial water content and water loss. Vermiculite lends itself well to such a quantitative study because the hydration state of the interlayer cations is fairly well understood, especially for Mg 2 § (Mathieson, 1958; Shirozu & Bailey