Use of Negative Sorption in Studies of Ion Fixation By Hydrobiotite

The exclusionof anions relative to tritiated water from the negatively charged interlamellar spacing of hydrobiotites that have a limited degree of lattice expansion permits measurement of the interlamellar volume. Measurement of the changes in the interlamellar volume and in the exchange capacity, when hydrobiotite lattices are collapsed by potassium treatment or expanded by treatment with sodium tetraphenyl boron, provides a means for estimating the distribution of the surface charge densities of these interstratified minerals. In the hydrobiotite sample studied (Zonolite from Traveler’s Rest, South Carolina), the biotite fraction was estimated to have a surface charge density of 2.0 ± 0.14 × 10−7meq cm−2and the vermiculite fraction, 1.5 ± 0.51 × 10−7meq cm−2. The charge density, and its relative distribution, was reflected in the tendency of these mineral fractions to collapse upon potassium treatment and to entrap trace concentrations of cesium in the interlayer spacing.