596 The overall recovery assessment further confirmed quinic acid as the most effective depressant, achieving approximately 35% REE recovery, whereas the other depressants resulted in recoveries of only 10–15%, as illustrated in Figure 4. Nevertheless, it should be emphasized that these recovery values remain well below those desirable for industrial application. Although the results reveal important trends regarding depressant performance, they clearly indicate the need for further optimization to improve system selectivity and increase REE grades in the concentrates. Given the limited depression efficiency observed for gangue minerals, it is likely that higher depressant dosages should be investigated in future studies in order to enhance REE selectivity and, consequently, overall recoveries. In addition, as suggested by Silva et al. (2023), the implementation of additional cleaning stages and regrinding steps may further improve the overall recovery of total rare earth oxides (TREO), particularly for complex carbonatite-hosted ores where REE-bearing minerals are finely intergrown with gangue phases. Figure 4 - Overall recovery of the main rare earth elements (REEs) obtained under different depressant conditions. 4. CONCLUSION The depressant dosages applied in this study were insufficient to achieve effective gangue rejection, highlighting the need for dosage optimization in future work. Sodium alginate showed potential as a gangue depressant, particularly for magnesium- and barium-bearing phases, contributing to improved selectivity. In contrast, quinic acid provided the highest REE recoveries, although with limited gangue suppression. Overall, the findings demonstrate that depressant selection and dosage play a critical role in balancing REE recovery and the concentrate quality in the flotation of Fen Deposit ores. ACKNOWLEDGMENTS This work was supported by: a) the European Union’s Horizon Europe Research and Innovation Program through the project REESOURCE Project under Grant Agreement number 101138460, b) UID/04028 - Research Center for Natural Resources and Environment – CERENA - funded by Fundação para a Ciência e a Tecnologia, I.P./ MCTES through the national funds. REFERENCES
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