Separation of lithium and cobalt from waste lithium-ion batteries via bipolar membrane electrodialysis coupled with chelation

A new type of process for separating metals in solution, based on bipolar membrane electrodialysis coupled with metal-ion chelation, is proposed. The method was 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 effects of initial EDTA concentration and pH were examined. Absorption of metal ions in the ion-exchange membranes was observed; this can be avoided by using a continuous semi-batch operation.