ADSORPTION OF HYDROLYZED POLYACRYLAMIDES ONTO AMPHOTERIC SURFACES

The adsorption of hydrolyzed polyacrylamide (HPAM) dissolved in distilled water onto sorbents with (SiO)2AlOH and SiOH surface sites was investigated as a function of pH and degree of hydrolysis τ (concentration ratio [COOH]/([CONH2] + [COOH]) of carboxylic to acrylamide plus carboxylic groups). (SiO)2AlOH is amphoteric and the densities of charged (SiO)2AlOH2+, (SiO)2AlO-, and non-charged (SiO)2AlOH species were calculated as functions of pH by potentiometric titration and electrophoretic mobility measurements. It was shown that the adsorption of noncharged polyacrylamide (τ = 0) was proportional to the density of (SiO)2AlOH sites. Adsorption occurred through AlOH...OC(NH2) hydrogen bonds and SiOH sites were inactive. At very low charge densities of the polymer, controlled by pH and the degree of hydrolysis τ, the driving force of adsorption became electrostatic in nature. The adsorption of HPAM was interpreted quantitatively on both sides of the pzc of the sorbent, taking into account the effects of the electrostatic potential of the sorbent and the density of (SiO)2AlOH2+ and (SiO)2AlO- surface sites. © 1990.