Thermodynamic Study on Adsorption of Sr(Ⅱ) on Palygorskite

The adsorption thermodynamics of Sr(Ⅱ) on palygorskite in aqueous solutions was investigated. In addition, the effects of contact time, ionic strength and pH were also investigated by static adsorption method. The results indicate that the adsorption of Sr(Ⅱ) on palygorskite is strongly affected by pH and ionic strength, and the ion exchange and surface complexation are the main adsorption mechanisms in the adsorption process. The adsorption kinetics of Sr(Ⅱ) on palygorskite can be described by Lagergren pseudo-second reaction rate model very well. The adsorption isotherm is fitted well by Freundlich and D-R models. Raising temperature is beneficial to adsorption reaction. The thermodynamic parameters, such as enthalpy (ΔH°), entropy (ΔS°) and Gibbs free energy (ΔG°) were calculated using adsorption equilibrium constant obtained from the Langmuir isotherm. The results indicate that the adsorption of Sr(Ⅱ) on palygorskite is a spontaneous and endothermic process.