THE PH-DEPENDENT COLLOIDAL STABILITY OF AQUEOUS MONTMORILLONITE SUSPENSIONS

The pH-dependent colloidal stability of aqueous montmorillonite suspensions was examined by coagulation and compression studies, and it was explained on the basis of calculations involving an ionization model and the classical DLVO theory. The intrinsic ionization constants (pKSOH=2.6 and pKTOH=6.4) and the ionizable site density (NS=4.8·1017 sites m-2) of montmorillonite prepared by ion exchange were determined experimentally. The total interaction energy as a function of 1:1 electrolyte concentration was calculated at different pH. The significant decrease of the stability of the suspensions with decreasing pH was verified experimentally. Suspensions at pH 2, 4 and 8 coagulated in the presence of 100, 200-250 and 350-400 mmol dm-3 NaCl, respectively. The values of VT,max relating to these concentrations are between 0.1 and 0.25 mJ m-2, hardly differing from one another. The results of compression studies on sodium- and hydrogen-montmorillonite suspensions likewise demonstrated the theoretically expected differences. © 1990.