Reactive separation of inorganic and organic ions in electrodialysis with bilayer membranes

Abstract This work shows the fundamental possibility of implementing the “reactive separation” of organic and inorganic ions from their mixtures using a bilayer membrane operating in a “mixed mode”. In this work, the electrodialysis process was studied during the processing of a solution containing a mixture of salts of inorganic and organic electrolytes. Sodium chloride was chosen as the inorganic electrolyte, and sodium acetate was chosen as the organic electrolyte. To study the peculiarities of ion transfer and the effect of chemical reactions occurring in the diffusion layer, electromembrane systems with a conventional anion-exchange membrane Ralex AMH and a BM-ac bilayer membrane (obtained by the authors) were studied. It is shown that the Ralex AMH membrane has a high selectivity to chloride ions and the permselectivity coefficient is P C l - / A c Σ = 3.3 . In the case of a bilayer membrane, which is an active source of hydrogen ions (appearing as a result of the water splitting reaction at the cation-exchanger/anion-exchanger interface), a reaction layer is formed inside the depleted diffusion layer, in which the recombination reaction of acetate ions and hydrogen ions proceeds. The use of a bilayer membrane makes it possible to increase the permselectivity coefficient up to P C l - / A c Σ = 61.4 . Simultaneously, in the under-limiting current mode, the bilayer membrane exhibits high selectivity to acetate ions, and the specific permselectivity coefficient is P C l - / A c Σ = 0.66 , which suggests the appearance of specific selectivity between singly charged ions during electrodialysis.