Due to the current widespread use of lithium-ion batteries in a range of applications, signi cant amounts of metalcontaining waste materials are generated. Typically, the recycling of transition metals from lithium-ion batteries involves leaching of Co 2 and Li from the LiCoO 2 anode and the electrolyte (e.g., LiPF 6 , LiBF 4 ). Thus, we herein examined the application of slug ow to the extraction of Co 2 and Li from an aqueous solution into an organic (cyclohexane) phase containing di-(2-ethylhexyl)phosphoric acid (D2EHPA) as the extraction reagent. The extraction equilibrium and extraction rate were then investigated to design a novel extraction process. In addition, a microchannel was employed to extract the Co 2 and Li ions from the aqueous phase. We found that the D2EHPA-Na solution (prepared from the partial exchange of H from D2EHPA with Na) was e ective for extracting Co 2 and, at a mole fraction of D2EHPA-Na >10%, complete Co 2 extraction from the aqueous phase was achieved. In addition, the presence of co-existing ions did not signi cantly a ect the extraction behavior of Co 2 and Li . Furthermore, the volumetric mass transfer coe cients (k L a) of Co 2 and Li exhibited the same order as those previously reported for other slug ow extraction systems. Finally, the ion concentration and selectivity were successfully simulated using the k L a values and the simulation results were in good agreement with experimental data. Such simulation of the Co 2 yield and purity is essential for selecting optimal process design conditions.

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Extraction by slug flow gives high mass transfer rate and rapid phase separation than the conventional extraction operation. Therefore, there are many advantages such as the volume of the device becomes small and the solvent drastically reduced. The slug flow extraction is expected as a sophisticated separation process. Especially, these advantages become more prominent in the multistage extraction. In this study, the extraction by the slug flow was applied to mutual separation of lithium, cobalt and nickel ions in the mixed aqueous solution. We succeeded in developing a process with lithium, cobalt, nickel ion purity of 85% or more and recovery rate of 90-95%. Furthermore, it was also confirmed that the flow state of the liquid is influenced by the hydrophobicity (PTFE) and hydrophilicity (glass) of the extraction tube. The overall mass transfer volumetric coefficient is affected by (1) the interface area of the oil phase and aqueous phase, (2) the strength of the circulating flow in each segment of the liquid, and (3) the volume flow ratio of the oil phase and the aqueous phase.