Recyclable and Reusable Fe₃O₄@Polydopamine for Valuable Metal Recovery from Spent Lithium-Ion Batteries

Acid leaching has attracted increasing attention for recovering valuable metals from spent lithium-ion batteries (LIBs), and additional reductant is required to improve leaching efficiency, in particular. However, the addition of reductant would not only increase costs but also make subsequent processing more difficult. Here, Fe3O4@polydopamine (PDA) is used as a green, recyclable, and reusable reductant, associating with citric acid to recover Li and Co from spent LiCoO2. Under optimal conditions, Li and Co have maximum leaching efficiencies of 99.02% and 98.02%, respectively. After magnetic separation, Fe3O4@PDA could be easily recycled and reused again for subsequent leaching. After three successive recycles, Li and Co have corresponding leaching efficiencies of 90.2% and 82.3%. Furthermore, the invalid Fe3O4@PDA is able to be renewed via a facile polymerization process, and the leaching efficiencies of Li and Co revert to 97.1% and 95.1%, respectively. The Li and Co in the leaching solution could be further recovered as Li2CO3 and Co3O4 via a simple precipitation process. Finally, a mechanism based on the analysis of cathode materials and Fe3O4@PDA before and after leaching is developed.