ACETAMIDE AND POLYACRYLAMIDE ADSORPTION CLAYS: INFLUENCE OF THE EXCHANGEABLE CATION AND THE SALINITY OF THE MEDIUM ONTO

Abstract--The adsorption of acetamide and partly hydrolyzed polyacrylamides onto montmorillonite has been investigated with emphasis on the valency of the exchangeable cation of the clay and the ionic strength of the medium. A difference in the adsorption of acetamide from 3 mg/g to 0.6 mg/g was observed when a Na+-clay was changed to a AP+-clay. For polyacrylamide, an opposite ffect was observed, and the fixation increased from 3 mg/g (Na+-clay) to 18 mg/g (AP+-clay). This difference in behavior may be ac-counted for by the decrease in adsorption sites due to partial flocculation in the presence of polyvaleut cations (tactoid formation). Adsorption in a saline medium is two- to fivefold greater for diverse polymers and substantially less for acetamide (from 3.0 mg/g to 0.77 rag/g). An increase in the degree of hydrolysis of the polymer esults in a significant increase in adsorption. In contrast, achange of molecular weight has practically no influence upon the adsorption ratio. The results obtained in saline medium may be explained by a size decrease of the macromolecules, allowing acloser approach to the surface of the mineral substrate, and by a chain lengthening as the degree of hydrolysis increases, induced by the electrostatic repulsions between the CO0- groups