Adsorption of cationic polyacrylamide onto kaolinite

The adsorption of the cationic polymer, polyacrylamide (PAM), onto kaolinite was investigated. Polyacrylamides are among the most commonly used polymers in industry and adsorption of PAM onto kaolinite from aqueous solutions have been investigated systematically as a function of some parameters such as calcination temperature of kaolinite, pH, ionic strength and temperature. According to the experimental results, the adsorption of PAM increases with pH from 5.50 to 10.50; temperature from 25 to 55 °C and ionic strength from 0 to 0.1 mol L−1. The kaolinite sample calcined at 600 °C has a higher adsorption capacity than the other calcined samples. Adsorption isotherms of PAM onto kaolinite have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The physical properties of this adsorbent are consistent with the parameters obtained from the isotherm equations. Furthermore, the zeta potentials of kaolinite suspensions have been measured in aqueous solutions of NaCl and different PAM concentrations and pH. From the experimental results, (i) pH strongly alters the zeta potential of kaolinite, (ii) kaolinite has an isoelectric point at about pH 2.35 in water and about pH 8 in 200 mg L−1 PAM concentration and (iii) PAM changes the interface charge from negative to positive for kaolinite. The study of temperature effect has been quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy. The dimensionless separation factor (RL) has shown that kaolinite can be used for adsorption of PAM from aqueous solutions.