The increasing availability of spent lithium-ion batteries (LIBs), which are rich in valuable metals such as nickel (Ni), cobalt (Co), and lithium (Li), makes them important secondary sources for metal extraction. This study focused on the recovery of Li from a flue dust generated during pyrometallurgical processing of NMC 622 battery material, where Li was present as Li₂CO₃ and LiF along with various impurities. To selectively extract Li, the flue dust was subjected to leaching with carbonated and limewater under varying temperature and S/L (solid/liquid) ratio. The leachates and leach residues were analyzed to determine Li recovery, co-leached impurities, and to identify possible factors limiting recovery. Leaching with carbonated water at an S/L ratio of 0.05 g/ml, 50 °C and pH of 7.5 resulted in a 70% recovery of Li over 60 min of leaching time, which reduced at higher S/L ratio and temperature. In contrast, when leaching with limewater at 75 °C and S/L ratio of 0.05 g/ml, 77% Li recovery was achieved within 10 min. During these conditions, the pH reached 10. SEM and XRD analysis revealed a CaCO₃ precipitate such as calcite, aragonite, and vaterite in varying proportions, causing surface passivation and inhibition of the leaching reaction. Leaching in limewater not only yielded higher Li recovery but also resulted in lower concentration of co-leached impurities (sodium, potassium, aluminum, and zinc), as compared to carbonated water leaching. However, the impurity levels remained high, requiring further purification and separation to produce battery-grade LiOH·H₂O. Graphical Abstract

The increasing demand for lithium-ion batteries (LIBs) has intensified the need for efficient lithium (Li) recovery from secondary sources. This study focuses on anti-solvent crystallization for the recovery of high-purity lithium hydroxide monohydrate (LiOH·H₂O) from a Li-rich leachate, derived from the flue dust of a pilot-scale pyrometallurgical process for LIB material recycling. To optimize product yield and purity, a series of experiments were performed, focusing on the influence of parameters such as solvent type, organic-to-aqueous (O/A) volumetric ratio, crystallization time, stirring rate, and anti-solvent addition rate. Acetone was identified as the most effective anti-solvent, producing rectangular cuboid crystals with approximately 90% Li recovery and around 95% purity, under optimized conditions (O/A = 4, 3 h, 150 rpm, and solvent flow rate of 5 mL/min). The flow rate influenced crystal morphology and impurity entrapment, with 5 mL/min favoring nucleation-dominated crystallization regime, producing ~20 μm of well-dispersed crystals with reduced impurity incorporation. SEM-EDS, surface washing, and gradual dissolution of obtained LiOH·H₂O crystals revealed that the impurities sodium (Na), potassium (K), aluminum (Al), calcium (Ca) and chromium (Cr) were crystallized as conglomerates. It was found that Na, K, Al, and Ca primarily crystallized as highly soluble conglomerates, while Cr was crystallized as a lowly soluble conglomerate impurity. In contrast Zn was distributed throughout the crystal bulk, suggesting either the entrapment of soluble zincate species within the growing crystals or the formation of mixed Li-Zn phase. Therefore, to achieve battery-grade purity, further purification measures are necessary.