Adsorption of arsenate from aqueous solution by ferric oxide-impregnated Dowex Marathon MSA anion exchange resin: application of non-linear isotherm modeling and thermodynamic studies

The characteristic of adsorption of As(V) onto ferric oxide-impregnated anion resin Dowex marathon MSA (FO-Dowex) was investigated. Batch adsorption experiment was studied as a function of pH, contact time, initial As(V) concentration, and temperature. The results revealed that the adsorption of As(V) onto FO-Dowex was highly pH-dependent and that the equilibrium time was attained within 360 min. Two-parameter equations (Langmuir, Freundlich, and Temkin) and three-parameter equations (Redlich–Peterson and Sips) isotherm models were used for modeling the experimental data for As(V) adsorption onto FO-Dowex at different temperatures through the non-linear regression method. The goodness of fit of the isotherm model to the experimental data was evaluated by comparing the statistical values of the coefficient of determination (R²), Chi-square (χ²) and the root mean square error (RMSE). From the isotherm analysis, the equilibrium data of As(V) adsorption onto FO-Dowex were found to be in good agreement with the Redlich–Peterson, Sips, and Langmuir isotherm model, based on the higher R² value and the lower values of χ² and RMSE as compared to other isotherm models. Furthermore, the calculation of thermodynamic parameters such as Gibbs free energy change (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) revealed that the adsorption process was feasible, spontaneous, and endothermic in nature. All the results suggested that FO-Dowex could be used an effective and potential adsorbent for the removal of As(V) from aqueous solutions.