Adsorption thermodynamic characteristics of U(VI) on modified corncob in aqueous solution

The corncob modified by KMnO4 in microwave was used for the adsorption of U(Ⅵ) ions from aqueous solution,and the thermodynamic characteristics on the adsorption were discussed.The results show that the adsorption capacity of the modified corncob increases with increasing temperature.Langmuir and Freundlich isotherms were used to fit the adsorption equilibrium data,and it is found that the adsorption process follows preferably the Langmuir isotherm adsorption model,which indicates that the adsorption mainly occurs in active region on the surface of modified corncob and belongs to the monolayer adsorption.The thermodynamic parameters,such as Gibbs free energy ΔG,enthalpy ΔH and entropy ΔS changes for the adsorption of U(Ⅵ) were calculated and discussed.When the concentration of U(Ⅵ) is below 80 mg/L,the Gibbs free energies of adsorption at all temperatures are negative and decrease with increasing temperature,which indicates that the adsorption process is spontaneous and the higher the temperature is,the greater the degree of spontaneous is.The entropy change ΔS and enthalpy change ΔH are positive,so the adsorption process is a heat absorption,the higher the temperature is,the more beneficial to adsorption is.