Study of the ion exchange equilibrium of Cl⁻, $NO_3^{ - }$, and $SO_4^{{2 - }}$ ions on the AMX membrane

Abstract

Equilibrium between the ion exchange membrane and solutions of anions at various valences has been the subject of this investigation. Competitive ion exchange reactions were studied on a strong base anion exchange membrane AMX manufactured by Tokuyama, commercialized by Eurodia, involving Cl⁻, ${\text NO}_3^{ - }$ and ${\text SO}_4^{{2 - }}$ ions. Solution concentrations studied were 0.05 and 0.1 M for all the systems reported. Experiments were performed with sodium as the counter ion, and the temperature was kept constant (T = 298 K). Ionic exchange isotherms for the binary systems—${{\text Cl}^{ - }}/{\text NO}_3^{ - }$, ${{\text Cl}^{ - }}/{\text SO}_4^{{2 - }}$, and ${\text NO}_3^{ - }/{\text SO}_4^{{2 - }}$—were established. The obtained results show that the sulfate was the most strongly sorbed, and the selectivity order is ${\text SO}_4^{{2 - }} > {\text NO}_3^{ - } > {{\text Cl}^{ - }}$ at 0.05 M and ${\text NO}_3^{ - } > {\text SO}_4^{{2 - }} > {{\text Cl}^{ - }}$ at 0.1 M under the experimental conditions. Selectivity coefficients $K_{{{{{\text Cl} }^{ - }}}}^{{{\text NO}_3^{ - }}}$, $K_{{2{{{\text Cl} }^{ - }}}}^{{{\text SO}_4^{{2 - }}}}$, and $K_{{2{\text NO}_3^{ - }}}^{{{\text SO}_4^{{2 - }}}}$ for the three binary systems were determined. All the results given by this membrane were compared with those obtained, in the same conditions, with the RPA membrane (produced by RHONE POULENC). Ternary equilibrium data were taken for ${{\text Cl}^{ - }}/{\text NO}_3^{ - }/{\text SO}_4^{{2 - }}$. The prediction of the ternary system based only on the binary data was consistent with the experimental data obtained for this system. The good agreement between the experimental and the predicted data showed that the proposed framework can be considered as an effective method to predict many ternary systems from binary systems.