The cation exchange capacity of a series of commercially available vermiculite-biotite minerals (Traveler’s Best, South Carolina; Libby, Montana; and Polobora, South Africa) was measured by a column method using various cations. The selectivity of the clay mineral for various ion pairs was determined with particular attention given to the adsorption from a sodium chloride-cesium chloride mixed electrolyte solution. The mineral was found to be highly selective for cesium ion, a large part of the amount adsorbed probably replacing potassium ions in the biotite layers. This replacement in the biotite is a much slower process than normal ion exchange and greatly lengthened the time required to come to equilibrium in the column.

The cesium ion cannot be removed easily from cesium-saturated vermiculite. The fixation of cesium ion was close to 100 percent at room temperature in contact with a cesium chloride solution. An isotopic exchange, Cs 133 for Cs 134, removed only very small quantities of the fixed cesium. Boiling with sodium chloride was only slightly more effective. All the results are in general agreement with the theory explaining ion fixation on the basis of collapse of the vermiculite structure to that of biotite.