RHEOLOGICAL SCALING OF MONTMORILLONITE SUSPENSIONS - THE EFFECT OF ELECTROLYTES AND POLYELECTROLYTES

This paper presents the results of investigations on flocculated alkal ine montmorillonite aqueous dispersions based on the scaling correlati on between rheological parameters and the clay weight fraction. Two ty pes of montmorillonite flocculation, induced by the presence of electr olytes, may be monitored from the scaling analysis of the rheological data: one produced by edge-face interactions occurring at a critical c oncentration of electrolyte and one derived from face-face interaction s occurring only in the presence of high concentrations of polyvalent cations. At the onset of edge-face flocculation the exponent of the sc aling function decreases from a value in the range 8-11, associated wi th a stable montmorillonite dispersion, to a value in the range 2-3. T he face-face coagulation produces, instead, a shift of the entire scal ing line towards higher montmorillonite concentrations without changes in the exponent. Anionic polyelectrolytes adsorbed on the clay surfac e weaken the network structure of the flocculated particles and therea fter deflocculate the dispersion, producing a partial recovery of the scaling exponent. It is suggested that the selective adsorption of pol yelectrolyte on the edges of the particles restores more effectively t he negative surface charge of the edges, thereby assisting the peptisa tion of the clay dispersion. Scaling analysis of the Bingham yield str ess of both flocculated and stabilised montmorillonite dispersions per mitted the evaluation of energy variations of the particle separation.