## 3 Results and Discussion
### Environmental Characterization  
Static prediction test results (paste pH and ABA) are given in Tables 4 and 5. The pH values, which are 7.77, 7.92, and 8.25 for the TSF1, TSF2, and TSF3 tailings, respectively, are indicative of non-acid-generating materials. Neutral to slightly alkaline pH can be related to the dissolution of neutralizing minerals such as carbonates and silicates [81]. The mechanical agitation of the suspension (liquid/solid) for 24 h shows that pH and conductivity are varying in the ranges of 3.46-3.94 and 57.3-68.9 mS/cm, respectively. Compared to the stirring for 48 h, these results indicate that the pH increases (5.12 to 5.64) while the conductivity decreases (58.7 to 37.4 mS/cm), which implied that there was a higher dissolution of potentially neutralizing minerals under acidic conditions. These results are in accordance with the high NP values during the agitation for 24 and 48 h for TSF1 (48.49 to 60.96 kg CaCO\({}_{3}\)/ t), TSF2 (48.58 to 61.17 kg CaCO\({}_{3}\)/ t), and TSF3 (49.75 to 61.89 kg CaCO\({}_{3}\)/ t) tailings. The AP values were below the NP values for all samples,  
Figure 13: Metallic trace element (MTE) patterns of the mine tailings (TSF1, TSF2, TSF3) and salt precipitates (TSF2S, TSF3S) compared to the upper continental crust (UCC: values are from [80]). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Composition (\%)** & **TSF1** & **TSF2** & **TSF3** \\ \hline Fe & 36.62 & 33.85 & 27.68 \\ FeO & 47.11 & 43.55 & 35.61 \\ Fe\({}_{2}\)O\({}_{3}\) & 52.36 & 48.4 & 39.57 \\ Fe\({}_{3}\)O\({}_{4}\) & 25.6 & 20.36 & 3.97 \\ Carbonates & 5 & 6 & 8 \\ Active limestone & 2 & 2 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Fe and Fe oxides and carbonate contents in the TSF tailings (NA: Not Analyzed). equalling 31.56 kg CaCO\({}_{3}\)/t, 31.25 kg CaCO\({}_{3}\)/t, and 13.12 kg CaCO\({}_{3}\)/t. According to [57], the NNP values can be correlated to the intervals 16.93-29.4 kg CaCO\({}_{3}\)/t, 17.33-29.93 kg CaCO\({}_{3}\)/t, and 36.63-48.77 kg CaCO\({}_{3}\)/t, respectively. According to [58], the NP/AP values are in line with the intervals 1.53-1.93 kg CaCO\({}_{3}\)/t for TSF1, 1.55-1.96 kg CaCO\({}_{3}\)/t for TSF2, and 3.79-4.72 kg CaCO\({}_{3}\)/t for TSF3. The authors noted that a prolonged digestion time has allowed dolomite to dissolve completely in the static test at room temperature as opposed to the 24 h test, resulting in more representative NP results. Afterwards, [9; 53] demonstrated that the Sobek test, modified by [54], underestimates the NP for samples containing dolomite and ankerite. Based on the mineralogical analysis, the AP values result from sulfide minerals oxidation. Taking into account the low NP of carbonates present in the tailings (dolomite, ankerite, siderite), the NP values are mainly provided by the dissolution of silicate minerals (phyllosilicates, amphiboles), which are mostly present in the TSF tailings as gangue minerals [82]. These silicates are potentially neutralizing minerals at pH = 5, as argued by [83; 84]. For the 48 h test, the pH increases and the EC decreases contrary to the 24 h test. This may indicate the precipitation of secondary phases and the retention of metals and metalloids by co-precipitation, adsorption or sorption. The criteria NNP and NP/AP adapted from [59] indicated that the acidity generation is uncertain for the tailings from TSF1 and TSF2 and non-acid generating for the tailings from TSF3 (Figure 14). However, based on the neutral pH paste imposed by a silico-carbonated matrix with a high neutralizing potential, the mine drainage is classified as contaminated neutral drainage (CND). However, once produced, CND can carry trace metals such as As, Cu, Ni, Co, Sb and Se, which are considered as potentially toxic elements with respect to the surrounding ecosystems [85].