ELECTROKINETICS OF NATURAL AND MECHANICALLY MODIFIED RIPIDOLITE AND BEIDELLITE CLAYS

Particles of clay minerals were studied due to their importance in geo chemical processes in natural waters, such as adsorption and transfer of ionic contaminants, stabilization by organics, and flocculation and sedimentation phenomena. Information on the behavior of clays was sou ght by experiments with model systems. Measurements of electrophoretic mobilities in relation to pH, at varying concentrations of well-chara cterized fulvic acid (FA), were performed on two structurally well def ined, representative clay minerals prepared with clean surfaces: ripid olite (a well-known trioctahedral nonswelling chlorite) and beidellite (a typical dioctahedral smectite). Natural ripidolite and beidellite show high negative electrokinetic potentials in the range pH 2(-10 and -20 mV, respectively) to pH 10 (-60 and -50 mV, respectively). Experi ments utilizing mechanical particle disintegration(dry milling), mimic king natural wear and physical weathering, resulted in increases of sp ecific surface area (12.3 and 1.5 times, respectively) and of cation e xchange capacity (3.2 and 1.2 times, respectively). Such small-sized p articles, shown by SEM figures, retain their crystal structure (X ray) and the nature of their structural bonds (FTIR), exhibiting an IEP (a t pH 6.0 and 3.0, respectively). This was interpreted to be the creati on of positively charged edge surfaces. Exposed to fulvic acid in solu tions of 10(-3) NaCl at pH = 6.5, these new surfaces showed an increas e in negative zeta-potential for ripidolite, and, to a smaller extent, for beidellite. In the interaction of clay mineral particles with aqu eous medium, it is concluded that the degree of mechanical wear is mor e decisive than the type of the mineral. (C) 1996 Academic Press, Inc.