ELECTROKINETICS OF PURE CLAY-MINERALS REVISITED

Clay minerals have long attracted the attention of colloid scientists, This paper considers, specifically, their important role in the trans port of various contaminants from land to sea, e.g., metal ions and or ganic detrital and man-made material in watercourses. Advances in expe rimental techniques have enabled precise characterization of clays and then electrokinetic experiments at high electrolyte concentrations, s uch as in seawater. Three of the most important clay minerals encounte red in suspended matter in natural waters, montmorillonite, illite, an d chlorite, were prepared in a very pure state. Electrokinetic experim ents were done in pure aqueous single and complex electrolyte solution s and in solutions in which natural organic matter was simulated using a humic substance, fulvic acid, of defined provenance and properties, typical of riverine waters. An isoelectric point was found at pH 5.0 +/- 0.2 for chlorite; none were found for illite and montmorillonite. Only Ca2+ showed a charging effect on chlorite, indeed a reversal of s ign from negative to positive at 1 x 10(-3) mol dm(-3). Addition of fu lvic acid affected only chlorite, illite less, and Na montmorillonite not at all. (C) 1996 Academic Press, Inc.