ELECTROKINETIC POTENTIALS OF CLAY SURFACES MODIFIED BY POLYMERS

This paper describes the influence of two polymers, fulvic acid (FA) a nd polyacrylic acids (PAAs) of comparable molecular mass, on the elect rokinetic potential of model surfaces encountered in clay minerals: si lica (SiO2), aluminum oxide (gamma-Al2O3), and gibbsite [gamma-Al(OH)( 3)]. Measurements at pH 6.5 +/- 0.2 show that FA and PAAs modifiy the potentials of aluminum oxide and gibbsite, but leave the silica surfac e unchanged. A chlorite clay mineral (ripidolite), milled to increase the numbers of oxy-hydroxy groups at newly created surfaces, was expos ed to FA and PAAs, carriers of carboxylic groups, to study their influ ence on electrokinetic potential. The key to the interaction is that p olymers hold metal ions (Al, Mg, Fe) in the edge surfaces, while silox ane groups show limited interaction or none at all. The results offer an explanation of why clay mineral particles are always negatively cha rged in natural waters. (C) 1997 Academic Press.