Influence of Exchangeable Cation Composition on the Size and Shape of Montmorillonite Particles in Dilute Suspension

Laurier L. Schramm and Jan C. T. Kwak
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada

Abstract: Viscosity and light-transmission measurements of dilute suspensions of montmorillonites having different exchangeable cations were used to calculate relative particle sizes as a function of cation composition, where particle size is expressed as the number of clay plates per tactoid relative to the number of plates per tactoid for Li-montmorillonite, after exchange of Li, Na, K, Cs, and Mg by Ca. Tactoid sizes increased in the order Li < Na < K < Mg < Ca, with the number of plates per tactoid relative to Li-montmorillonite varying from 1.5 for Na- to 6.1 for Ca-montmorillonite. The results for tactoid sizes derived from light transmission and those derived from viscosity data are in reasonable agreement with each other and with literature data for similar systems. Upon exchange of Ca-counterions for Li-, Na-, or K-counterions, a sharp initial decrease in tactoid size was observed over approximately the first 30% of cation exchange. Upon further exchange, tactoid sizes changed only slightly, but when Ca was exchanged for Cs or Mg, a much more gradual decrease in particle size was observed.

Key Words: Exchange cations • Light transmission • Montmorillonite • Particle size • Tactoid • Viscosity

Clays and Clay Minerals; February 1982 v. 30; no. 1; p. 40-48; DOI: 10.1346/CCMN.1982.0300105
© 1982, The Clay Minerals Society
Clay Minerals Society (www.clays.org)