The aim of this study is to evaluate the applicability of adsorption models for understanding the thermodynamic properties of adsorption process. For this study, the adsorption isotherm data of NO3-N ion onto a commercial anion exchange resin obtained at various experimental conditions, i.e. different initial concentrations of adsorbate, different dosages of adsorbent, and different temperatures, were used in calculating the thermodynamic parameters and the adsorption energy of adsorption process. The Gibbs free energy change (ΔG o ) of adsorption process could be calculated using the Langmuir constant bM as well as the Sips constant, even though the results were significantly dependant on the experimental conditions. The thermodynamic parameters such as standard enthalpy change (ΔH o ), standard entropy change (ΔS o ) and ΔG o could be calculated by using the experimental data obtained at different temperatures, if the adsorption data well fitted to the Langmuir isotherm model and the plot of ln b versus 1/T gives a straight line. As an alternative, the empirical equilibrium constant(K) defined as qe / Ce could be used for evaluating the thermodynamic parameters instead of the Langmuir constant. The results from the applications of D-R model and Temkin model to evaluate the adsorption energy suggest that the D-R model is better than Temkin model for describing the experimental data, and the availability of Temkin model is highly limited by the experimental conditions. Although adsorption energies determined using D-R model show significantly different values depending on the experimental conditions, they were sufficient to show that the adsorption of NO3-N onto anion exchange resin is an endothermic process and an ion-exchange process.
The aim of this study is to evaluate the applicability of adsorption models for understanding the thermodynamic properties of adsorption process. For this study, the adsorption isotherm data of NO3-N ion onto a commercial anion exchange resin obtained at various experimental conditions, i.e. different initial concentrations of adsorbate, different dosages of adsorbent, and different temperatures, were used in calculating the thermodynamic parameters and the adsorption energy of adsorption process. The Gibbs free energy change (ΔG o ) of adsorption process could be calculated using the Langmuir constant bM as well as the Sips constant, even though the results were significantly dependant on the experimental conditions. The thermodynamic parameters such as standard enthalpy change (ΔH o ), standard entropy change (ΔS o ) and ΔG o could be calculated by using the experimental data obtained at different temperatures, if the adsorption data well fitted to the Langmuir isotherm model and the plot of ln b versus 1/T gives a straight line. As an alternative, the empirical equilibrium constant(K) defined as qe / Ce could be used for evaluating the thermodynamic parameters instead of the Langmuir constant. The results from the applications of D-R model and Temkin model to evaluate the adsorption energy suggest that the D-R model is better than Temkin model for describing the experimental data, and the availability of Temkin model is highly limited by the experimental conditions. Although adsorption energies determined using D-R model show significantly different values depending on the experimental conditions, they were sufficient to show that the adsorption of NO3-N onto anion exchange resin is an endothermic process and an ion-exchange process.
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