Solvent extraction recovery of critical metals: A comparative study using black mass and separated cathode material from spent Li-ion batteries

Recycling spent lithium-ion batteries (LIBs) is essential for sustainable resource recovery and environmentally responsible waste management. This study presents an integrated hydrometallurgical recycling process incorporating selective and sequential solvent extraction to efficiently separate and purify valuable metals from complex leachates derived from two NMC-derived spent LIB feed forms, namely separated cathode material and black mass. Leaching was conducted at 60°C for 60 min under conditions optimized separately for each feed form. For the separated cathode material, optimal leaching was achieved using 1 M H 2 SO 4 with 3 vol% H 2 O 2 at an S/L ratio of 50 g/L, whereas the impurity-rich black mass required 1.5 M H 2 SO 4 with 7 vol% H 2 O 2 and a S/L ratio of 75 g/L to reach leaching efficiencies exceeding 98% for Li, Ni, Mn, and Co. The solvent extraction process consisted of selective and sequential separation stages, including feed-form-dependent extraction of Mn using saponified D2EHPA, followed by stepwise separation of Co and Ni using saponified Cyanex 272, as well as subsequent scrubbing and stripping to obtain purified metal sulfate solutions. The use of solvent extraction enabled selective separation of chemically similar transition metals and produced precursor solutions suitable for crystallization. Final crystallization yielded manganese sulfate, cobalt sulfate, nickel sulfate, and lithium phosphate with phase purities exceeding 99.75% for both investigated feed forms. The overall recoveries were approximately 67–85%, depending on the metal and feed form, demonstrating the technical feasibility of the proposed solvent-extraction-based recycling strategy for the two NMC-derived feed forms investigated in this study. Although a fraction of each metal is lost during the single-cycle process, these unrecovered metals could, in principle, be recovered by reintroducing them into subsequent extraction cycles.