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 c lay plates. None of the models based on this assumption offers a unive rsal treatment of the relationship between solvent properties and swel ling. It is suggested that the swelling of clays may be described by a n extension of the regular solution theory. Of 11 solvents tested, swe lling of a mixed layer illite/smectite was greatest in N-methylformami de but that of a Na-montmorillonite was greatest in water, contradicti ng the assertion that swelling is correlated with solvent is-an-elemen t-of. Permeability of beads of spray-dried Cu-montmorillonite (r = 3.5 mum) to hexane-2-propanol, 2-propanol-methanol, and methanol-water mi xtures was measured by pumping the solvents at a rate of 1 mL/min thro ugh an HPLC column. The highest intrinsic permeability (k) was observe d in 2-propanol with lower k values in mixtures of both higher and low er is-an-element-of.