Selective Separation of Metal Ions via Bipolar Membrane Electrodialysis Coupled with Chelation

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A new type of process for separating metals in solution is proposed, and applied to a mixed solution of lithium and cobalt, as in the recycling of waste lithium-ion batteries. When a chelating agent, ethylenediaminetetraacetic acid (EDTA), was added to a mixed solution of lithium ions and cobalt ions, almost all the cobalt ions were chelated by EDTA to form anions, whereas lithium ions were hardly chelated, at pH > 4. Electrodialysis of the feed solution was conducted using a three-cell-type electrodialysis system, with a unit consisting of two ion-exchange membranes and a bipolar membrane. Lithium was transported to the lithium recovery cell and cobalt was transported to the cobalt recovery cell, using an applied electric field. The selectivity for each metal in the recovery cell was about 99%. The separation system was also applied to Li-Co-Mn and In-Al systems, and its separation performance was studied.e