## 3 Results and Discussion
### Characterization of the Inputs and Output Products of the Phosphate Laundries
#### 3.1.3 Geochemistry
This result shows, firstly, that Cr is essentially associated both to the clay-phosphate fraction and organic matter [29], especially at Redeyef, and secondly, as stipulated by [PERSON] et al. [8], this result shows that most of this element recorded in fine wastes derives from the corrosion of the process installations (chrome steel-made hydroxycones). Uranium distribution shows small fluctuations between the raw phosphates (31 mg/kg for RP-ZL and 28.7 mg/kg for RP-R) and the marketable phosphates (28.87 mg/kg for MP-ZL and 35.1 mg/kg for MP-R). With regards to wastes, U concentrations revealed a small decrease in terms of coarse wastes at M'Dhilla (22.87 mg/kg). Yet, this decrease was noticed with both cases, coarse and fine wastes, at Redeyef (19.35 mg/kg and 23 mg/kg, respectively). These findings indicate that U is evenly distributed between the phosphatic phase and the exogangue at M'Dhilla but is closer to the phosphatic phase at Redeyef. In terms of raw phosphates, Pb displayed the lowest concentration rate among trace elements (3.9 mg/kg for RP-R and 5.15 mg/kg for RP-ZL). The levels recorded in the output products are slightly variable but more significant in the fine wastes (4.37 mg/kg for FW-ZL and 8.9 mg/kg for FW-R) (Table 3). In another respect, and compared to other sedimentary rocks, it is generally known that REEs are enriched in marine phosphorites [37; 40; 41; 45; 46; 47]. In our samples, and even though characterized by patterns similar in shape, the REEs show variable concentration rates (Table 3), all of which display a slight enrichment in light REEs (LREEs), compared to heavy REEs (HEREs), along with negative Ce and Tb anomalies and a positive Eu anomaly (Figure 3). The cerium anomaly indicates that phosphate has formed in a suboxic to oxic marine environment that is deficient in this element [48]. However, the Tb anomaly, which was previously reported for phosphates in the Gafsa-Metaoui Basin [8; 33; 40; 49; 50], should be relevant in terms of analytical problems only [12; 51; 52]. According to [PERSON] [53], the variations in the Eu contents result from the reduction of this element to the valence 2+, deriving from the modifications observed in the redox conditions. In another respect, the input products (RP) from the two laundries bear almost similar total concentrations (REE of around 204.39 mg/kg for M'Dhilla and 218.66 mg/kg for Redeyer). Similarly, and although the marketable phosphates from both laundries bear more significant total contents in REEs (248.68 mg/kg for MP-ZL and 251.29 mg/kg for MP-R), the coarse and fine wastes still carry considerable quantities of REEs at M'Dhilla-Zone L (184.3 mg/kg and 210.32 mg/kg, respectively) but much lower total contents at Redeyer (114.42 mg/kg and 125.27 mg/kg, respectively). The high contents of REEs in the fine wastes of M'Dhilla are strongly related to their P\({}_{2}\)O\({}_{5}\) content (16.87%). As indicated by [PERSON] [30], it can be stated that REEs have an affinity for phosphates because of their substitution for Ca\({}^{2+}\) in the apatite structure, on the one hand, and their correlation with the organic matter present in pellets, on the other.