Overcoming heterocoagulation challenge in selective flotation separation between lithium cobalt oxide and lithium manganese oxide

• Froth flotation can be used to separate and purify different spent cathode materials . • Hydroxamate-type collector can hydrophobize lithium cobalt oxide cathodes. • Heterocoagulation between different cathode materials is a challenge in separation. • Dispersants can be used to mitigate the heterocoagulation effect. • New flotation chemistries are developed to improve cathode materials recycling. Efficient separation of mixed cathode active materials from recycled Li-ion batteries is a prerequisite for both the successful direct recycling and hydrometallurgical recycling of spent lithium-ion batteries (LIBs). In this work, separation between lithium cobalt oxide (LCO) and lithium manganese oxide (LMO) was investigated using the froth flotation method. Sodium octanohydroxamate (OHA) was employed as the collector. It was found that individual LCO materials could be selectively hydrophobized by OHA and floated by air bubbles, while LMO materials could not be floated using OHA as the collector. Unfortunately, the flotation separation of a binary mixture of LCO and LMO in DI water was poor due to the heterocoagulation between these two cathode materials. With the addition of sodium metasilicate as the dispersant, the flotation separation of the two was significantly improved. The mechanism was investigated using ζ-potential measurements, SEM analysis, and DLVO force analysis. It was found that the ζ-potentials of both LCO and LMO were slightly negatively charged at a pH of 7 to 9, resulting in the heterocoagulation between the two cathode materials. The addition of sodium metasilicate increased the magnitude of negative ζ-potential and therefore improved particle dispersion and separation efficiency. The present work demonstrated the importance of dispersants in the separation of mixed cathode materials from Li-ion batteries.