## 3 Results and Discussion
### Characterization of the Mineral by XRD
#### 3.3.2 Characterization of the Mineral Composition in Output Streams  
Figures 6, 7, and S6 and Table S9 show the main results obtained by XRD analysis. In particular, Figure 6 shows a comparison of the diffraction patterns of the mineral collected from the different output streams during the concentration process, starting with the 70 run-of-mine mineral and using C40 as dense medium (Figure S6 show results obtained with the same mineral after desliming 70D). It is evident that the characteristic peaks of celestine are always higher in the under stream, which has coarser particles UH. Figure 7 shows the mass percentages of the different mineral phases detected in the different output streams. In all cases, the stream with the higher celestine grade is the UH stream, the highest being the C40 medium, with or without desliming. Even though celestine is concentrated and recovered mostly in the under streams (especially in the coarse size fraction UH), the main gangue mineral phase (calcite) appears in significant amounts in the under stream in the finer fraction mineral (UL). This is reasonable as calcite is associated with celestine in the run-of-mine mineral but has a finer particle size [2]. Calcite particles bound to heavier celestine crystals could be drawn into the under stream. Figures 7 and S6 show the distribution of the mineral phases present in the OL, OH, UL, and UH samples recovered after the concentration process. In the experiments using the CG medium, the mineral recovered from the under stream (UL and UH) has a significantly higher concentration of celestine than that recovered from the over stream. This demonstrates the efficiency of the density separation process and that heavier celestine particles are preferentially drawn into the underflow streams. For the other media suspension, the results are more variable. Nevertheless, in all cases, the highest concentration of celestine was obtained in the UH stream (under stream and larger particle size fraction, above 250 \(\upmu\)m). In the experiments using the C40 dense medium, the percentage of celestine \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **Celestine (\%)** & **Stroncianite (\%)** & **Quartz (\%)** & **Dolomite (\%)** & **Calcite (\%)** \\ \hline
70 & 67.45 & 2.03 & 6.79 & 8.08 & 15.01 \\
70D & 69.28 & 1.81 & 3.54 & 9.04 & 15.55 \\ \hline \end{tabular}
\end{table} 
Table 1: Mineral composition of the run-of-mine mineral samples (fed in the input stream) determined by XRD analysis. Figure 6: Comparative XRD patterns of samples collected from the over (OH, OL) and under (UH, UL) streams with C40 dense medium that have a particle size higher (H) or lower (L) than 250 \(\upmu\)m. Illite (llt); celestine (Cel); calcite (Cal); quartz (Qtz). obtained in the over streams (OH and OL) and UL stream is very similar (differing by less than 2%) (OH: 63.51% celestine; OL: 64.64% celestine; UL: 66.36% celestine). When CG, F and FM media are used, the percentage of celestine in the OH and OL streams are lower than the corresponding percentages in the under streams. Mineral desliming increases the concentration of celestine, especially in the OL stream, as demonstrated in Figure S6. Desliming exhibits significant beneficial results in some mine processing. It is considered a critical factor for yield and avoids the pulping process [40,41]. In this case, desliming increases the concentration of celestine in the over stream with smaller size fraction (OL). Other studies, which used flotation concentration methods, demonstrated the best way to increase mineral concentration was to remove the fines as they hinder sedimentation [42,43]. Celestine concentration in the output streams  
Figures 8 and S7 show the concentration/percentage of celestine (main phase detected) for each output stream (over O or under U) with particle sizes higher (H) or lower (L) than 250 \(\upmu\)m, without considering the total mineral mass recovered.