ELECTRODIALYSIS OF ACID-SOLUTIONS WITH METALLIC DIVALENT SALTS - CATION-EXCHANGE MEMBRANES WITH IMPROVED PERMEABILITY TO PROTONS

The electrodialysis of acid solutions (chlorhydric and sulfuric) in th e presence of metallic divalent salts (chloride and sulfate) are studi ed. The anion-exchange membranes used in this process have been select ed from several membranes manufactured by Solvay because of their low water content and their good anionic selectivity. Two kinds of cationi c exchange membranes have been tested: the No. 9, a homopolar prototyp e membrane, manufactured by Solvay, which was selected after several t ests; and a commercial cation-exchange membrane (CDS membrane), which has been modified on its surface by adsorption of polyelectrolyteimine . The obtained results show that HCl+CuCl2 or NiCl2 and H2SO4+CuSO4, N iSO4 or ZnSO4 can be treated by electrodialysis using the selected CEM . Tn all cases the acid is not only more concentrated but also purer t han when traditional CEM are used. Some problems appeared with the mix ture HCl+ZnCl2 because of complexes formation between Zn2+ and Cl- ion s.