Leakage of mono- and divalent cations through the weak-base anion exchange membrane in the process of electrodialysis of H2SO4 and its metal salt mixture

Experimental results on the separation of sulfuric acid from its mixture with sodium- and magnesium sulfate, respectively, by the electrodialytic method have been presented. The Selemion AVV membrane as anion-exchange membrane was used. It was found that the leakage of Na+ from the cathode to the anode side of the AAV was higher than that of Mg2+. The leakage of Na+ decreased with the acid concentration whereas that of Mg2+ increased. Surprisingly enough, the permeability of Na+ increased with the electric current density, indicating a substantial contribution of electroosmotic convection to the Na+ flow. The current efficiency of the anions transport (HSO4 -, SO4 2-) through the AAV hardly exceeded 50%. It was independent of the kind of salt present on the cathode side of the AAV.