Separation of Graphites and Cathode Materials from Spent Lithium-Ion Batteries Using Roasting–Froth Flotation

Abstract

The separation of graphites and cathode materials from spent lithium-ion batteries (LIBs) is essential to close the loop of material used in LIBs. In this study, the roasting characteristics of the spent LIB materials are carefully analyzed, and the effects of roasting on the surface morphology and elemental chemical states of electrode materials are fully investigated by thermogravimetric analysis, SEM-EDS, and XPS to explore the roasting–flotation enhancement mechanism. Then, froth flotation is utilized to separate the graphites and cathode materials from the spent LIB materials. The optimal roasting temperature is determined by thermogravimetric analysis and the SEM-EDS analysis of the spent LIB materials. The results suggest that the organic binder can be effectively removed from the spent LIB materials at the roasting temperature of 500 °C, and there is almost no loss of graphite. The XPS results indicate that, in the process of roasting, the decomposition products of the organic binder can easily react with valuable metals (Ni, Co, and Mn) to produce corresponding metal fluoride. The flotation results of the spent LIB materials after roasting at the optimal conditions indicate that graphites and cathode materials can be efficiently recovered through roasting–froth flotation. When the dosage of kerosene is 200 g/t and the dosage of methyl isobutyl carbinol (MIBC) is 150 g/t, the cathode materials grade is 91.6% with a recovery of 92.6%, while the graphite grade is 84.6% with a recovery of 82.7%. The roasting–froth flotation method lays the foundation for the subsequent metallurgical process.

The Recycling of Spent Lithium-Ion Batteries: Crucial Flotation for the Separation of Cathode and Anode Materials

“…If the temperature is too high, the cathode graphite will burn. Figure 4 d shows the thermogravimetric analysis (TGA) results of the black mass [ 54 ]. It can be seen that the temperature for removing the organic coating should be in the range of 450 °C to 550 °C.…”

“…Flotation experiments were carried out on the roasted modified black mass to investigate the effect of the collector and frother dosages on the flotation separation efficiency. After flotation, further purification operations can be carried out to obtain high-purity graphite and cathode material products, which can realize the recovery of graphite from spent LIBs [ 54 ].…”

“…Thermal treatment can completely remove the organic coating on the surface of electrode material, increase the difference in wettability between LFP and graphite, and improve the flotation separation efficiency [ 44 , 54 , 55 , 56 , 57 , 59 , 60 ]. As shown in Figure 7 a, the best roasting conditions for removing the organic coating on the surface of electrode material were achieved at 500 °C for 1 h. The recovery and enrichment ratios of Li after flotation were 95.87% and 1.37, respectively, while those of Fe were 95.25% and 1.36, respectively.…”

“…2020, Elsevier, ( d ) thermogravimetric analysis of the raw spent LIB material Reprinted with permission from Ref. [ 54 ]. 2022, MDPI, ( e ) contact angles of the pyrolytic electrode materials at different pyrolysis temperatures: (I) anode material and (II) cathode material Reprinted with permission from Ref.…”

“…Based on this, many researchers have borrowed the flotation separation method of LCO and graphite to study the flotation separation of NCM and graphite. Previous studies have shown that methods such as roasting and pyrolysis can effectively remove the organic coating on the surface of the electrode material, expose the original surface of the electrode material, increase the difference in wettability between the cathode and anode materials, and enable flotation to effectively separate the cathode and anode active materials (Figure 6a) [54][55][56][57]59,60]. After the roasting of the black mass composed of NCM and graphite particles, the organic binder and residual electrolyte on the surface of the electrode material were effectively removed, and there was no significant loss of graphite.…”