Electrotransport of HCl in anion exchange membranes for the recovery of acids. Part II. Kinetics of ion transfer at the membrane-solution interface

In the first part of this work, the equilibrium properties of three anion exchange membranes specially designed for the recovery of acid have been presented. In this second part, the anion exchange membranes were again clamped between symmetrical aqueous solutions of HCl, but they were submitted to an electrical field. Measurements of unidirectional fluxes of HCl allowed to determine the transport numbers of the chloride ion and showed that the AAV and the ARA membranes presented practically the same proton leakage while the ACM membrane was less permselective. The concentration profiles were calculated on the basis of the Nernst-Planck electrodiffusion equations, within the unstirred layers. Combining the current-overvoltage characteristics and the experimental fluxes of Cl−, it was possible to obtain the values of the apparent rate constants of the penetration for the chloride ions and protons into the membrane. The reduced proton leakage observed in the lower HCl concentration range was due to the higher value of the rate constant of Cl− through these membranes. But, as the HCl concentration increased in the aqueous solution, the rate constant of the penetration of Cl− decreased while that of proton remained practically constant.