Figure 3 - Main REEs in the products (O: Overflow, U: Underflow) of the flotation tests in the first and second stages in the presence of different depressants: (a) phytic acid, (b) quinic acid, (c) sodium alginate and (d) citric acid. 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.
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