Competition of NH3 and H2O for Adsorption Sites on Clay Minerals

Ammoniation of air‐dry Ca, Mg, and Al montmorillonite and bentonite resulted in dehydration of the exchangeable cations and a change in c‐axis spacing from 15 to 16Å. to 12.6 to 13Å. Ammoniation of a vacuum‐dried Ca system resulted in a change in c‐axis spacing from 10.1 to 12.3Å. On the other hand, NH 3 retained by the minerals upon ammoniation was replaced by H 2 O under controlled conditions of relative humidity. It was postulated that the mutual competition between H 2 O and NH 3 molecules for adsorption sites can be described by the law of mass action. The various theories which have been proposed to describe the mechanism of NH 3 chemisorption are discussed.