SEPARATION OF AG+, ZN2+ AND CU2+ IONS BY ELECTRODIALYSIS WITH A MONOVALENT CATION SPECIFIC MEMBRANE AND EDTA

In this work, electrodialysis is applied to the separation of the cations from a mixture of the electrolytes AgNO3, Zn(NO3)2 and Cu(NO3)2 in aqueous solution when the metal ion concentrations are low (0.01 M). The commercial cation exchange membrane Neosepta C.M.S., produced by Tokuyama Soda, which is selective for monovalent ions, was used. In order to prevent scale formation on the membrane, nitric acid or ammonia is added to the feed solution. In both cases the current efficiencies of Ag+ recovery are low because of the competitive transport of protons or ammonium ions through the membrane. The separation of silver from copper and zinc has been performed using EDTA as a complexing agent. Because the charges of the complexes formed have different signs, silver is obtained with an acceptable yield in the cathodic side, whereas the copper and zinc are obtained in the anodic side with low current efficiency.