Effect of Gas Over-Saturation Degree on Flotation Separation Performance of Electrode Materials from Spent Lithium-Ion Batteries

The electrode materials from spent lithium-ion batteries consist of graphite and lithium cobalt oxides (LCO), which cannot be efficiently separated by conventional flotation technique due to fine size distributions of graphite and LCO. In this work, nanobubbles were introduced to the flotation system of electrode materials. Nanobubbles were produced with the method of temperature difference. The different degrees of gas over-saturation in water/slurry were created by increasing temperature of cold water stored in a 4℃ environment at least 72 h to the terminal 20℃, 25℃, 30℃ respectively. It was founded that height and lateral distance of nanobubbles increased with the degree of gas oversaturation of water. Besides, the larger graphite agglomerations were observed to form in the presence of nanobubbles. The D50 (chord length) of graphite agglomerations increased by 8 μm, 11 μm and 21 μm respectively compared with the D50 of graphite in natural water. More graphite agglomerations adhered to a captive bubble with aid of nanobubbles than the case of no nanobubbles, which was indicated by increased wrapping angles of graphite (agglomerations) adhering to a captive bubble. Furthermore, the maximum adhesion force between a captive bubble and substrate increases to 220, 270, 300 μN as cold water temperature increases to 20, 25 and 30℃. The frost of nanobubbles on graphite surface and thus resulting in graphite agglomerations by bridging effect of nanobubbles together should be responsible for the improved flotation performance of electrode materials. The present results indicate that flotation performance of fine minerals can be regulated by regulating gas oversaturation degree of slurry.