K+ ⇌ Na+ ion exchanges and availability of two groups of exchange sites in a vermiculite. II. Variability of the equivalent fraction of the two groups / Echanges d'ions K+ ⇌ Na+ et existence de deux groupes de sites d'échange dans une vermiculite. II. Variabilité des fractions équivalentes des deux groupes

Abstract

Water-swollen K-and Na- vermiculites in flakes, 1 to 2 mm in size, were equilibrated with aqueous solutions of K+ and Na+ (and Cl-) ions, at 26, 60 and 90 °C. The shape of the isotherms and the types of vermiculites involved revealed the existence of two groups of cation exchange sites corresponding to the alternate interlayer spaces. These two site groups are responsible for two cation exchange reactions. The equivalent fractions of the two groups are equal or unequal, according to the working conditions. Unequal equivalent fractions correspond to a metastable electronic structure of the layers. Complex isotherms are broken up into two simple isotherms. The exchange standard thermodynamic functions were calculated. A structural interpretation was proposed.