ELECTROTRANSPORT OF SULFURIC-ACID IN SPECIAL ANION-EXCHANGE MEMBRANES FOR THE RECOVERY OF ACIDS

The transport properties of anion exchange membranes specially designed for the recovery of acids by electrodialysis were studied using aqueous H2SO4 solutions. When the membranes were not submitted to any driving force, measurements of sorption, water content, self-diffusion flux, electrical conductivity and results of Raman spectroscopy showed that the membranes cannot be accounted for by a classical gel-phase model and, on the other hand, that only HSO4- ions balanced the exchanging sites. The apparent mobilities of these ions and of SO42- ions in the interstitial region were also determined. When the membranes were submitted to an electrical field, measurements of unidirectional fluxes by the radiotracer technique showed that, even for diluted H2SO4 solutions, the value of the transport number of SO42- ions never exceeded 0.85 for the membranes bearing weak basic exchanging groups while it reached unity for the membrane bearing strong basic exchange groups. This phenomenon was attributed to proton transfer reaction between exchanging groups and HSO4- ions. This reaction favored the proton leakage. For higher H2SO4 concentrations the membranes bearing weak basic groups presented a reduced proton leakage.