Electrodialysis of LiPF ₆ in Aqueous Solution for Wastewater Treatment in Hydrometallurgical Recycling of Lithium‐Ion Batteries

In the deactivation of spent lithium‐ion batteries (LIBs) by crushing in water for small‐scale recycling, one of the most difficult challenges is the treatment of wastewater containing LiPF 6 due to the slow decomposition rate of PF 6 − . Additionally, the recovery of dissolved Li + in wastewater is required. This study aims to separate PF 6 − and Li + from wastewater containing LiPF 6 by electrodialysis. LiPF 6 solution is prepared as the feed, and PF 6 − and Li + are transferred into the anolyte and catholyte through an anion exchange membrane (AEM) and a cation exchange membrane (CEM), respectively. The transport numbers of PF 6 − and Li + in the AEM and CEM are measured as 0.22–0.32 and 0.22–0.50, respectively. Then, the effects of the compounds derived from LIBs electrolyte, ethylene glycol, and formic acid on the electrodialysis are investigated. In addition, the transport chemistry of LiPF 6 is discussed by comparing the electrodialysis of LiPF 6 with that of NaCl. The higher permselectivity of PF 6 − in the AEM is explained by the hydrophobicity of anions. Finally, the operation costs of wastewater treatment are estimated. This estimation suggests that electrodialysis has the potential to significantly reduce the cost of wastewater treatment.