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Competition of NH₃ and H₂O for Adsorption Sites on Clay Minerals¹

ABSTRACT

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, NH₃ retained by the minerals upon ammoniation was replaced by H₂O under controlled conditions of relative humidity. It was postulated that the mutual competition between H₂O and NH₃ 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 NH₃ chemisorption are discussed.

¹ Technical paper no. 1765, Oregon Agr. Exp. Sta., Corvallis. This paper includes portions of a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree at Oregon State University. Presented before Div. S-2, Soil Sci. Soc. Am., at Ithaca, N. Y., Aug. 21, 1962.

² Formerly Instructor, Oregon State University, now Assistant Soil Scientist, Washington State University, Irrigation Exp. Sta., Prosser, and Professor of Soils, Oregon State University, Corvallis, respectively.

Received for publication January 10, 1964. Accepted for publication May 11, 1964.