Enhancement effect of interfacial nanobubbles on flotation performance of electrode materials from lithium-ion batteries

Flotation separation of valuable components including graphite and lithium cobalt oxide (LCO) from the waste electrode materials of lithium battery is a key link in the recycling of waste lithium battery, which is difficult to realize with some conventional flotation techniques due to the fine size of graphite and LCO. Interfacial nanobubbles induced by temperature increasing were introduced into the flotation system and the mechanism on improving the flotation performance of electrode materials by nanobubbles was studied by combining intermittent mode atomic force microscope (AFM) imaging technique, colloidal probe technique, agglomeration size analyzer, particle-bubble interaction visualization and flotation. The results show that the images of nanobubbles were captured at highly oriented pyrolytic graphite (HOPG) and alumina surface with intermittent mode AFM. The detachment and/or coalescence of nanoentities in the action of AFM tip at contact mode provided evidence supporting gaseous nature of these nanoentities. The maximum adhesion force between graphite and HOPG in-creased in the presence of nanobubbles between graphite and HOPG. The maximum adhesion force was lower than 10 nN in the room temperature water while up to 110 nN in the cold water, which varied with the pH variation in slurry. It was observed that the larger graphite agglomerations were induced by interfacial nanobubbles. The size of such graphite agglomerations increased by 2−11 μm in the cold water compared with that in the room temperature water. The nucleation of interfacial nanobubbles on graphite surface and the formation of graphite agglomerations synergistically enhanced the adhesion between graphite and fixed bubbles. The flotation results showed that the flotation performance was always improved with nanobubbles in all slurry with different pH values and ions concentrations.