Reactivity of Montmorillonite Surfaces with Weak Organic Bases

The adsorption of organic amines and pyridines was used to study the reactivity of magnesium and calcium‐saturated montmorillonite surfaces. The ability of clays to chemisorb organic bases of different pk b values was used as a measure of the acid strength of their surface. Chemisorption and physical adsorption of the organics were differentiated by infrared analysis of the organic‐clay complex. Nontronite and Otay bentonite are the most reactive of the montmorillonites studied, being able to chemisorb bases with pk b values greater than 11.4. The active sites on Wyoming bentonite were found to be heterogeneous with respect to acid strength. The majority of the sites reacted with organic bases with pk b values of 8.8 and below, but chemisorbed only a small amount of aniline and m ‐chloroaniline which have pk b values of 9.4 and 10.5, respectively. Hectorite chemisorb bases with pk b values of 8.8 and below but did not chemisorb a base with a pk b of 9.4.