## 3 Results and Discussion  
### Assessment of the Tailings' Heterogeneity at the Micro Scale  
The particle size and morphology in the tailings' body varied in unpredictable ways, as Figure 4 shows. The SEM images reveal aggregated particles that appear amorphous (Figure 4a-c). Figure 4d shows the presence of particles with crystalline shapes. The point-specific EDS  
Figure 4: Representative SEM images of the sampled tailings: (**a**) image of fine particles; (**b**) image of an aggregate of particles; (**c**) image showing a rugged surface morphology of tailings; (**d**) image specific to crystalline particles. Figure 3: Images of incremental sampling: (**a**) sampling from a depth of 50 cm; (**b**) fine waste sample; (**c**) coarse waste sample. analysis performed on the tailings depicted in Figure 4 indicates chemical heterogeneity at the micro scale (Figure 5). The EDS analysis in Figure 5a shows concentration values that are significantly different from those in Figure 5b. Notably, U is measured in the second specimen (Figure 5b), while in the first one (Figure 5a) it is undetected. These findings from the SEM and EDS investigations support the hypothesis of assigning uniform distribution to the quantities of trace elements in the tailing aliquots. The XRFS measurements yield results that must be interpreted as mean values at a scale of approximately 1 Kg, as the collected sample was homogenized prior to subsampling the aliquot used for testing. The XRFS results include both major and minor components of the tailings, as presented in Table 1, which lists the results for aliquots no. 1 and no. 22. These aliquots were randomly chosen to ensure that there was no bias regarding the XRFS analyses. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Description Method: TurboQuant Pellets**} \\ \hline  & \multicolumn{2}{c}{**Aliquot No. 1**} & \multicolumn{2}{c}{**Aliquot No. 22**} \\ \hline \multirow{2}{*}{**Z**} & \multirow{2}{*}{**Symbol**} & **Concentration** & *** SD** & **Concentration** & **SD** \\  & & **[**\%wt.]** & **[**\%wt.]** & **[**\%wt.]** & **[**\%wt.]** \\ \hline
11 & Na2O & 0.804056 & 0.024000 & 1.794032 & 0.023658 \\
12 & MgO & 1.344708 & 0.009000 & 1.358216 & 0.007707 \\
13 & Al2O3 & 9.817325 & 0.010000 & 9.686015 & 0.009131 \\
14 & SiO2 & 52.68028 & 0.0300 & 49.572850 & 0.032995 \\
15 & P2O5 & 0.642814 & 0.001700 & 0.642621 & 0.001823 \\
16 & SO3 & 2.324803 & 0.009000 & 3.449874 & 0.000920 \\
17 & Cl & 0.014883 & 0.000070 & 0.014575 & \(7.19\times 10^{-5}\) \\
19 & K2O & 2.030205 & 0.006000 & 2.188351 & 0.005578 \\
20 & CaO & 11.38931 & 0.00900 & 14.84444 & 0.008259 \\
22 & TiO**2** ** **0.855457** & 0.004500 & 0.812547 & 0.004797 \\
23 & V2O5 & 0.01414 & 0.00130 & 0.013785 & 0.001213 \\
24 & Cr2O3 & 0.025996 & 0.000460 & 0.024948 & 0.000407 \\
25 & MnO & 0.11524 & 0.00070 & 0.113313 & 0.000781 \\
26 & Fe2O3 & 15.62105 & 0.00400 & 13.89942 & 0.003672 \\
27 & **CoO** & 0.001607 & 0.000230 & 0.001600 & 0.000234 \\
28 & NiO & 0.006846 & 0.000100 & 0.006134 & 0.00011 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Representative XRFS test report for aliquots no. 1 and no. 22 from the sampling set of 40 samples. Figure 5: EDS spectra associated with Figure 4 and elemental analyses associated with each spectrum: (**a**) EDS spectrum associated with Figure 4b; (**b**) EDS spectrum associated with Figure 4d. The analytical range of the Xepos instrument covers many of the CRMs (V, Ga, Ge, Rb, Y, Nb, Mo, Ag, Cd, Sb, Te, La, Ce, Hf, Cs, and Bi) as well as heavy metals (As, Cd, Cr, Hg, Pb, and Se). The XRFS results indicate that these elements are at trace levels in these tailings (Table 1). Given that the analysis of CRMs in the tailings using XRFS is of greater current interest than that of heavy metals, the application of the developed model for statistical data analysis focused on selected CRMs. For instance, the concentrations of La, Te, and Hf are below their respective LOQ values, while those of Ga, Y, and Sr exceed their respective LOQs.