On the analysis of monovalent-ion selectivity of anion-exchange membranes

The scientific community has shown great interest in the selectivity of anion-exchange membranes (AEMs), particularly regarding their ability to monovalent-ions selective transport. In this work, we have studied the selectivity of an original anion-exchange membrane and a layer-by-layer (LbL) surface-modified membrane in the electrodialysis (ED) desalination of sodium chloride and sodium sulfate mixture in a lab-scale cell. The effect of various experimental factors on the desalination process and the selectivity of the separation of ions with different charges, such as the composition of the concentrate compartment, electrolyte concentrations in the concentrate and diluate compartments (0.004-0.5 M), the specific current value (0.82-9.0 mA/cm2), the desalination time, and the stirring of solution were considered. To explain the observed patterns, diffusion experiments and numerical simulations using the COMSOL (R) software package were carried out. Our findings demonstrate that the method chosen for conducting the benchmark desalination of a mixture of chlorides and sulfates can significantly affect the values of the selectivity coefficients and the accuracy of their determination for both standard and surface-modified membranes. For the latter, varying the desalination conditions leads to improved P(Cl/SO4) due to modification of up to 40 %.