Enhanced flotation of graphite using Micro-Nano bubbles from the black mass of spent lithium-ion batteries

The separation of cathode and anode materials is essential for recycling spent lithium-ion batteries (LIBs). Due to graphite’s high hydrophobicity, flotation is the preferred method for separating black mass, graphite in the anode material is suitable for flotation due to its high hydrophobicity, but its fine particle size (<15 um) hinders particle-bubble collision and true flotation. However, the fine particle size of electrode materials hinders effective separation in conventional flotation. Therefore, micro-nano bubble enhanced flotation was investigated, and its mechanism was analyzed. Both micro-nano and conventional flotation methods were compared to assess their efficiency in graphite separation under varying parameters. The graphite concentrate grade peaks and then declines with slurry concentration, kerosene, and methyl isobutyl carbinol (MIBC) dosage, while recovery rises and then stabilizes. Under the optimal conditions of a flotation time of 3 min, a pulp density of 40 g/L, a kerosene dosage of 300 g/t, and an MIBC dosage of 150 g/t, the graphite grade of the micro-nano bubble flotation concentrate can reach 89.22 %, with a recovery rate of 85.83 %. Under the optimal conditions, the flotation rate constant k of micro-nano bubble flotation reaches 0.779, while conventional flotation only achieves 0.492, indicating that micro-nano bubbles significantly enhance the flotation separation performance. Contact angle measurements and optical microscopy revealed that micro-nano bubbles enhance the hydrophobicity of graphite and promote particle aggregation.