bastnäsite, parisite, synchysite, and monazite. The material was subjected to a grinding unit with a roll diameter of 200 mm, aiming to achieve a particle size below 80 μm, suitable for direct flotation tests. Following the crushing and grinding stages, the samples were characterized in terms of particle size distribution, semiquantitative elemental chemical composition by X-ray fluorescence (XRF) using a portable X-MET7500 analyzer (Oxford Instruments), and gamma-emitting radionuclide activities (40K, 232Th, and 238U), measured with a GT-40 gamma spectrometer (Georadis). In addition, the rare earth element content of the sample was quantitatively determined by inductively coupled plasma mass spectrometry (ICP-MS). 2.2 Flotation tests Flotation experiments were conducted in two sequential stages, aiming to maximize the recovery of rare earth elements (REEs). The tests were performed using an adapted laboratoryscale flotation setup consisting of a 600 mL beaker-based flotation cell immersed in a water bath to maintain the pulp temperature at 50 °C, as illustrated in Figure 1. This configuration ensured adequate mineral surface activation and collector dissolution throughout the experiments. Agitation was maintained at 400 rpm, and the pulp pH was controlled under mildly alkaline conditions, at approximately 8.3. In the first flotation stage, 180 g of feed material was processed, corresponding to a solids concentration of approximately 25 wt.%. In the second stage, 100 g of the underflow material obtained from the first stage was used, resulting in a solids concentration of about 15 wt.%. This two-stage configuration was adopted to enhance REE recovery from both the initial feed and the partially depleted material. Hydroxamate-based collectors, specifically octanohydroxamic acid, were selected due to their higher selectivity towards REE-bearing minerals compared to other reagent classes, such as carboxylates and phosphoric acid esters (Kim, Choi and Lee, 2025). Quinic acid, phytic acid, sodium alginate, and citric acid were evaluated as depressants. Identical collector concentrations were applied across all tests, while the performance of the different depressants was comparatively assessed. Sodium chloride (NaCl) and sodium hydroxide (NaOH) were used for pH adjustment and control at approximately 8.3, which has been reported to favor flotation performance (Zhang et al., 2019). Following flotation, all products were filtered, dried at 60 °C for 24 h, weighed, and subsequently analyzed for REE content by inductively coupled plasma mass spectrometry (ICPMS).
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