## 5 Conclusions
It is worth noting that froth flotation, identical to conventional flotation of primary resources, remains a highly effective method for isolating end-of-life products containing REEs, particularly for separating phosphors from glass in spent fluorescent lamps. Meanwhile, the other flotation techniques were primarily applied to isolate REEs from wastewater, showcasing their effectiveness in separating bulk REEs. These flotation technologies not only contributed to wastewater treatment but also facilitated the recovery of REEs, aligning with the principles of sustainable development and supporting the UN Sustainable Development Goals (Goal 12: Responsible consumption and production). However, it is important to highlight that the separation of individual REE ions through flotation techniques still lacks extensive study. This represents a challenging topic for future research, focusing on enhancing flotation technologies by investigating the effects of important parameters such as surfactant selection, solution pH, and electrolyte conditions. By addressing this research gap, advancements can be made in optimizing flotation processes for individual REE separation. We believe that this review is beneficial for stakeholders across various disciplines, including those working in fundamental research studies, policy development, mineral processing, and extractive metallurgy, as well as waste management and recycling. It offers a fundamental understanding of conventional and advanced flotation, presents key concepts, and provides numerous ideas for developing future technologies in the REMs industry. By utilizing the concepts and insights presented in this systematic review, stakeholders can drive advancements and innovations in REMs processing and REE recycling, ultimately contributing to the growth and sustainability of the industry. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13148364/s1](https://www.mdpi.com/article/10.3390/app13148364/s1)]([https://www.mdpi.com/article/10.3390/app13148364/s1](https://www.mdpi.com/article/10.3390/app13148364/s1)), Figure S1: Study selection flow diagram. ; Figure S2: Chemical structure of typical three collector types mostly used in REMs flotation (a) carboxylate, (b) hydroxamate, and (c) organo-phosphoric acid. ; Figure S3: (a) Adsorption mechanism of collector on REM surface; (a-1) chemisorption and (a-2) surface reaction, and (b) chemisorption modes; (b-1) bridge, (b-2) monentate, and (b-3) bidentate. ; Table S1: Lists of 17 REEs and 84 REMs used as searching keywords. ; Table S2: Summary of recent studies on REM flotation using other collectors [3; 3; 29; 31; 32; 33; 34; 35; 63; 64; 65; 66; 67; 68; 69; 70; 71; 72; 73; 74; 75; 76; 77; 78; 79; 80; 81; 82; 83; 84; 85; 86; 87; 88; 89; 90; 91; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101; 102; 103; 104; 105; 106; 107; 108; 109; 110; 111; 112; 113; 114; 115; 116; 117; 118; 119; 120; 121; 122]. Conceptualization, P.J., A.N., L.T., O.J. and T.P. ; methodology, P.J., O.J., P.S., C.B.T. and T.P. ; software, P.J. and P.S. ; validation, P.J., C.B.T. and T.P. ; formal analysis, P.J. and P.S. ; data curation, P.J. and P.S. ; writing--original draft preparation, P.J., A.N., L.T., O.J., P.S., C.B.T. and T.P. ; writing--review and editing, P.J., K.A., I.P., M.I., C.B.T. and T.P. ; visualization, P.J. and T.P. ; supervision, A.N., M.I., C.B.T. and T.P. ; project administration, P.J. and T.P. ; funding acquisition, T.P. All authors have read and agreed to the published version of the manuscript. This research is funded by Chulalongkorn University (ReinUni_65_02_21_06). Not applicable. The authors wish to thank the members of the Faculty of Engineering, Chulalongkorn University, for their support to this project and gratefully acknowledge the editors and anonymous reviewers for their valuable inputs to this paper. The authors declare no conflict of interest.