Kinetic, equilibrium and thermodynamic studies for phosphate adsorption on aluminum hydroxide modified palygorskite nano-composites

Abstract

The objectives of this study were to synthesize aluminum hydroxide modified palygorskite nano-composites (Al–PG) and to investigate their suitability as adsorbents to remove phosphate from aqueous solution. The nano-composites were characterized by XRD, XRF and TEM. The characterization results showed that aluminum hydroxide gel was successfully loaded onto palygorskites (PGs) with diameters of nanometers, and the crystal composition of PG had not been changed after modification. The effects of modified mass ratios, pH, co-existing anions, and initial phosphate concentrations on phosphate removal were investigated by batch experiments. The Freundlich model provided a better description for the adsorption process than the Langmuir model. The maximum phosphate adsorption capacity was 16.86 mg g⁻¹ for Al–PG, while it was 4.08 mg g⁻¹ for natural PG. Of the adsorption isotherms and thermodynamic studies considered, the adsorption of phosphate by Al–PG was chemisorption, endothermic and spontaneous. Kinetic studies indicated that the adsorption of phosphate onto Al–PG can be fitted by a pseudo-second-order kinetic model very well. Thus, the cost-effective and high adsorption capacity of Al–PG has wide potential use in phosphate removal from aqueous solutions.