Characterization of Montmorillonite Saturated with Short-Chain Amine Cations: 2. Interlayer Surface Coverage by the Amine Cations

Abstract

AbstractPortions of Wyoming bentonite were saturated with a series of short-chain aliphatic amine and quaternary ammonium cations, and the amine content remaining after washing was determined by combustion analysis. For those amine cations containing one or two carbon atoms, the amount of amine found was greatly in excess of the cation-exchange capacity. It is thought that this excess consists of amine cations or uncharged amine molecules which have become partly embedded in the holes associated with the oxygen rings of the silica sheet surfaces. For the larger tertiary amine cations, slightly less than the exchange capacity was found, presumably owing to blocking of some exchange sites by steric interference.Upon treatment of the amine-saturated clays with glycerol and quantitative determination of the glycerol retained as a monolayer, it was found that these clays retain considerably less glycerol than the original bentonite. The glycerol retention values were employed to provide quantitative estimates of the interlayer clay surface left unoccupied between cation pillars. The percentage of original interlayer surface left unoccupied ranged from about 75 percent for methylamine to essentially zero for the larger tertiary amine cations.The validity of the areas calculated from the glycerol retention results was indirectly confirmed by deriving estimates of the cross-sectional areas of the several cations from the observed reductions in amount of glycerol retained. These experimentally derived cross-sectional areas were found to be in satisfactory agreement with areas of the cations projected from atom models.