Separation of Cobalt and Nickel Ions Using Electrodialysis Reversal in the Presence of Ethylene Diamine Tetraacetic Acid

This paper describes selective separation of cobalt and nickel ions from their mixed solution using the electrodialysis reversal (ED-R) process. In experiments using the conventional electrodialysis process, the fluxes of cobalt and nickel ions were almost identical under the conditions used. Conversely, when electrodialysis experiments were conducted in the presence of Ethylene Diamine Tetraacetic Acid (EDTA), cobalt ions preferentially permeated through a cation-exchange membrane and were well separated. Based on these results, cobalt and nickel ions were permeated into a compartment containing an EDTA aqueous solution by normal electrodialysis operation, and then ED-R was performed with the polarity reversed to separate the cobalt and nickel ions. The ED-R -operation facilitated to effectively separate the nickel and cobalt ions. We also attempted to recover the nickel ions and EDTA from their mixed solution using a precipitation method. The recovery rate of EDTA reached 80％, and the solution turned green at a lower pH of 0.4.