On the applicability of DLVO theory to the prediction of clay colloids stability

The stability behavior of Na-montmorillonite colloids has been studied by c ombining the analysis of their surface charge properties and time-resolved dynamic light scattering experiments. The chemical surface model for severa l types of clays, including montmorillonite, has to take into account the d ouble surface charge contribution due to their permanent structural charge and to their pH-dependent charge, which is developed at the edge sites, the refore, these stability studies were carried out as a function of both ioni c strength and pH. DLVO theory is largely applied for the prediction of the stability of many colloidal systems, including the natural ones. This work shows that the stability behavior of Na-montmorillonite colloids cannot be satisfactorily reproduced by DLVO theory, using the surface parameters exp erimentally obtained. Particularly this theory is unable to explain their p H-dependent stability behavior caused by the small charge at the edge sites . Based on these results, a literature review of DLVO stability prediction of clay colloids was performed. It confirmed that this theory is not capabl e of taking into account the double contribution to the total surface charg e and, at the same time, pointed out the main uncertainties related to the appropriate use of the input parameters for the calculation as, for example , the Hamaker constant or the surface potential. (C) 2000 Academic Press.