Froth flotation of lithium-ion battery black mass: A cathode-chemistry-resolved review of pretreatment strategies, surface thermodynamics, flotation kinetics, and equipment design

The accelerated adoption of electric vehicles necessitates scalable recycling technologies for spent lithium-ion batteries (LIBs). Froth flotation exploits the inherent difference in hydrophobicity between graphite and hydrophilic cathode active materials (CAM); however, this contrast is not universally preserved: residual binder, solid electrolyte interphase (SEI) products and electrochemical ageing may lower the graphite contact angle, promote heterocoagulation (slime coating) of cathode fines onto graphite, or alter dispersion and dissolved-ion chemistry, so that their net effect on selectivity depends on cathode chemistry and conditioning history. This review organises the flotation literature by cathode chemistry (NCM, LCO, LFP) and, going beyond a simple chemistry-based classification, links cathode surface chemistry, pretreatment response, flotation kinetics, entrainment behaviour, and equipment selection into a single explanatory framework. The reviewed literature suggests that a single reagent regime is unlikely to be effective across cathode chemistries, consistent with reported differences in zeta potential and ion hydration among CAMs. The available evidence suggests that the effective thermal treatment window (approximately 400–550 °C) is associated with decomposition of the PVdF-containing surface layer and recovery of the graphite contact angle, and that this window depends on cathode composition. A state-of-health (SoH)-resolved two-rate-class kinetic framework is proposed as a testable hypothesis linking electrochemical ageing to flotation rate constants; it has not yet been validated against controlled-SoH flotation data. For ultrafine black mass, conventional mechanical flotation cells appear to be strongly limited by hydraulic entrainment of hydrophilic slimes; column and pneumatic flotation cells, which employ wash water to suppress this non-selective entrainment, are identified as plausible candidate technologies rather than demonstrated solutions, pending pilot-scale validation on spent LIB black mass. Overall, this review provides a mechanistic, chemistry-resolved basis for pretreatment and equipment selection in LIB black-mass flotation, while identifying kinetic model validation and pilot-scale testing as priority directions for future work.