Adsorption of Polycarboxylate-based Superplasticizer onto Natural Bentonite

Abstract

The adsorption of polycarboxylate-based superplasticizer onto natural bentonite was investigated in aqueous solution using a batch technique with respect to initial adsorbate concentration, contact time, temperature, pH value and ionic strength. Lower pH value and higher ionic strength were proved to be favorable for the adsorption. The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to describe the kinetic data and the kinetic constants were also determined. The experimental data fitted the pseudo-second-order model well. The Langmuir, Freundlich and Dubinin-Radushkevich (D-R) equations were applied to describe the equilibrium isotherm and the isotherm constants were also evaluated. The langmuir model agreed with the experimental well. Thermodynamic parameters (ΔG⁰, ΔH⁰ and ΔS⁰) indicated that the adsorption was endothermic and physical in nature.