SOME COLLOIDAL PROPERTIES OF BEIDELLITE - COMPARISON WITH LOW AND HIGH CHARGE MONTMORILLONITES

Recent evidence of the occurrence of beidellite in many soils around t he world necessitates a better understanding of the role of charge loc ation on the colloidal behavior of this smectite as compared to the mo re frequently studied montmorillonites. Clay suspension stability and sorption of an organic polymer, two properties sensitive to surface ch arge characteristics, were selected to examine the differences in coll oidal behaviors of these smectites. The Otay montmorillonite was shown to have a higher charge than either the beidellite or the SWy-1 montm orillonite. Even though structural formulae resulted in a higher perma nent charge for the beidellite as compared to the SWy-1, effective cha rge of these two smectites is the same. The pH dependency of the criti cal coagulation concentration of the smectites could not be explained based only on edge charge considerations, and it is proposed that tetr ahedral charge location enhances the pH effect on the CCC. Decreased p oly(vinyl) alcohol sorption with either increasing surface charge or t etrahedral charge location was observed. Both parameters affect the ea se of replacement of water molecules by PVA on the surface of smectite s.