Preparation and Solvation Properties of Some Variable Charge Montmorillonites

Li-, Na-, K- and Ca-saturated Wyoming montmorillonites have been prepared and used to obtain Li.Na-, Li,K-, and Li,Ca-montmorillonites with a range of Li contents. These were heated at 220°C for 24 hr, causing the Li+ ions to migrate mainly into the layer structure and leaving varying amounts of Li+, Na+, K+, and Ca2+ ions in the interlayer positions as determined by exchange with NH4+ ions. The results are only partially consistent with a migration of the Li+ ions into vacant octahedral sites up to the limit of the octahedral layer charge. Solvation of the resulting clays with water and various organic liquids showed the following results: With water, acetone and 3-pentanone, expansion of the montmorillonites increased in a step-wise manner with increasing numbers of interlayer cations qualitatively in accord with the field strength of the cations and the dipole moments of the molecules. With ethanol, ethylene glycol and morpholine, swelling with each liquid was practically independent of the number of interlayer cations, within the limits of the prepared materials. It is suggested that for the second group of liquids some mechanism additional to cation-dipole interactions, such as hydrogen bonding to silicate oxygen surfaces, may play an important part.