ADSORPTION OF POLYMERS ON CLAYS AS AFFECTED BY CLAY CHARGE AND STRUCTURE, POLYMER PROPERTIES, AND WATER QUALITY

Abstract

The adsorption of a family of polysaccharides (guar) and a family of polyacrylamides (PAM) by clays from aqueous solutions was studied. Anionic, nonionic and cationic polymers were investigated. Silver Hill illite (IM-1) was equilibrated with two synthesized waters which represented the quality of the Friant-Kern Canal water and of well water used for irrigation in the San Joaquin Valley of California. The electrical conductivity of these waters was 0.05 and 0.7 dS m−1, and the sodium adsorption ratio was 0.43 and 1.75, respectively. The adsorption of the polymers on this illite was compared to their adsorption on Wyoming montmorillonite which was measured under the same conditions in a previous study. The order of adsorption of the polymers was cationic > nonionic > anionic in all systems. The cationic and nonionic polymers adsorbed to a larger extent from the canal water than from the well water, whereas the anionic polymers displayed a higher adsorption from the well water. The results suggest that the adsorption of the polymers occurred mainly on the external surface of the clay packages (tactoids or quasicrystals). The structure of the micro-aggregates (floccules), which the clay packages formed in the presence of the polymers or electrolytes, and the pore size distribution in these micro-aggregates had a dominant effect on the adsorption of the polymers. The water quality also influenced the adsorption considerably. The higher the electrolyte concentration, the higher was the rate of clay flocculation, and the fraction of the surface area which was found inside the intra-aggregate cavities was, hence, less accessible. The competition between inorganic cations and the cationic polymers adsorption for sites on the negatively charged clays also increased with the electrolyte concentration. Since an increase in the electrolyte concentration results in a compression of the electric diffuse double layer at the clay surface and enhances neutralization of the charge of the anionic polymers, the adsorption of these polymers increased with the electrolyte concentration, as opposed to the decrease in the adsorption of the cationic and nonionic polymers as this concentration increased.