Swelling Properties of Synthetic Smectites in Relation to Lattice Substitutions

Abstract
Synthetic clays were prepared hydrothermally at 300° to 350°C and 15,000 psi from gels with compositions calculated to give a series of octahedrally and tetrahedrally substituted, 2:1-type layer silicates with charges of 0.5N, 1N, 1.5N, 2N, 2.5N, and 3N, where N equals the “normal” layer charge of montmorillonite. Besides montmorillonites and beidellites, the products also contained other components, kaolinite, saponite, paragonite and possibly amorphous materials, depending on the initial gel compositions. Cation exchange capacities of µ fractions treated for removal of amorphous constituents were within the narrow range of 0.95–1.35 meq per g rather than 0.45–2.70 meq per g as calculated from initial gel compositions. Comparisons between the expanding properties of these materials showed that the beidellites expanded less readily than the montmorillonites upon solvation with glycerol vapor and tended to give single interlayer complexes. These differences were most pronounced when Mg was the saturating ion, although they were also apparent with Ca. The K-saturated montmorillonites gave greater expansion than the beidellites on hydration at 100 per cent r. h. The montmorillonites also exhibited greater rehydration than the beidellites after heating at 400°–500°C. Beidellite exhibits properties of expansion that are intermediate between those of montmorillonite and vermiculite. The results of this investigation are consistent with the existence of somewhat stronger ionic attractions in the beidellites than in the montmorillonites. The source of the charge thus has an effect upon the properties of expansion.