Equilibrium, Thermodynamic, and Kinetic Studies of the Adsorption of 2,4-Dichlorophenoxyacetic Acid from Aqueous Solution by MIEX Resin

The study investigated the performance of 2,4-D adsorption on MIEX resin. The different temperatures affecting the adsorption performance were specifically evaluated. Equilibrium data followed the Freundlich and Langmuir isotherm model for all investigated temperatures (283 K to 333 K). The Langmuir model was slightly better than the Freundlich model at a lower temperature (283 K); however, with the increase of temperature the Freundlich model could well describe the isotherm data. The solute coefficient of distribution (Kd) could be better used to estimate the thermodynamic parameters compared with the Langmuir equilibrium constant (KL). The thermodynamic parameters (ΔH0, ΔS0, and ΔG0) showed that the adsorption of 2,4-D was feasible, endothermic, and spontaneous at 283 K to 313 K. The activation energy (Ea, 47.70 kJ·mol–1) determined by using the rate constant k2 of pseudo-second order model (the suitable kinetic model) and the mean free energy value (Efe, 6.0348 kJ·mol–1) evaluated by using the Dubinin–Radushkevich (D–R) model indicated that chemical ion-exchange was the predominant mechanism of 2,4-D adsorption. The calculated film diffusion coefficient value (Df) suggested film diffusion was the kinetic rate-limiting step. The adsorbent displayed excellent reusability with 0.1 mol·kg–1 NaCl as the regeneration agent.