CLAY SWELLING AND REGULAR SOLUTION THEORY

Expansion and contraction of clays in contact with solvents have been often attributed to the influence exerted by the dielectric constant (is-an-element-of) of the solvent on the equilibrium distance between clay plates. None of the models based on this assumption offers a universal treatment of the relationship between solvent properties and swelling. It is suggested that the swelling of clays may be described by an extension of the regular solution theory. Of 11 solvents tested, swelling of a mixed layer illite/smectite was greatest in N-methylformamide but that of a Na-montmorillonite was greatest in water, contradicting the assertion that swelling is correlated with solvent is-an-element-of. Permeability of beads of spray-dried Cu-montmorillonite (r = 3.5 mum) to hexane-2-propanol, 2-propanol-methanol, and methanol-water mixtures was measured by pumping the solvents at a rate of 1 mL/min through an HPLC column. The highest intrinsic permeability (k) was observed in 2-propanol with lower k values in mixtures of both higher and lower is-an-element-of.