Sol formation ability of Ca/Na-montmorillonite at low ionic strength

Various colloidal phases of Wyoming type Ca/Na-montmorillonite have been investigated experimentally by sedimentation and swelling tests of originally pure Ca- or Na-montmorillonite in different CaCl2/NaCl solutions of low ionic strength. Forces contributing to colloid (de)stability are discussed, and the experimental findings are compared with a theoretical sol formation zone in the [Ca2+]–[Na+] diagram derived from simple assumptions regarding the forces. It is found that the sol formation ability drastically lowers when calcium ions are present in the system. This effect could be due to an explicit influence of these ions on edge face interactions.