Collector Regimes in Lithium-Ion Battery Flotation: A Systematic Review and Bibliometric Analysis

The growing volume of end-of-life lithium-ion batteries (LIBs) is necessitating the development of physical separation processes that recover electrode materials while reducing downstream recycling burdens. This systematic review and bibliometric analysis examined LIB flotation research published from 2016 to 2025. Scopus and Web of Science (WoS) databases were searched, and items were screened using predefined eligibility criteria following the PRISMA guidelines 2020, yielding 79 eligible publications. These studies were classified into (i) collector-free (n = 9), (ii) non-ionic (n = 62), (iii) ionic (n = 6), and (iv) unspecified-reagent systems (n = 2). Pretreatment has been reported as an essential step for improved liberation and surface accessibility, as well as better control of aggregation and aqueous chemistry. Collector-free flotation was effective when graphite retained sufficient hydrophobicity, but selectivity was constrained by residual binders, ultrafine entrainment, particle aggregation, and solution chemistry. Meanwhile, non-ionic hydrocarbon collectors dominated the literature, primarily enhancing graphite floatability rather than imparting intrinsic selectivity against cathode active materials. In addition, flotation performance depended strongly on pretreatment, collector dispersion, frother behavior, reagent sequence, hydrodynamics, and circuit configuration. In contrast, ionic collectors were less studied and were used mainly for copper–aluminum separation and differential flotation of blended cathode materials. Unspecified-reagent systems integrated flotation with direct recycling and graphite regeneration, but incomplete reporting limited comparison. Across all regimes, feed heterogeneity and surface condition strongly governed separation efficiency. Finally, a universally superior collector regime was not found because reagent selection strongly depended on feed characteristics and the intended separation objective, product requirements, and extent of process integration.