## 3 Results and Discussion
### Discussion  
The fine petrographic, mineralogical, and geochemical characterization showed significant differences between the two sludge samples analyzed. Equally, the particle-size distribution showed that the sludge from the Redeyef laundry is enriched in fine fraction (82.84%) compared to that from M'Dhilla-ZL (58.87%). The mineralogical study showed the presence of the following minerals in the two fine wastes: CFA, clinoptiolite, calcite, dolomite, gypsum, ankerite, quartz, and other silicates, such as smectite and palygorskite. We also deduced that the latter are more abundant in the fine wastes of the Redeyef laundry. The wet processing of raw phosphate is a simple physical process of granulometric classification resulting in the separation of the merchant ore (71 \(\upmu\)m-2000 \(\upmu\)m) enriched in CFA, from the fine (-71 \(\upmu\)m) and coarse (+2000 \(\upmu\)m) fractions enriched in gangue minerals (carbonates, silicates, etc.). Chemical analysis showed that carbonates, P\({}_{2}\)O\({}_{5}\), U, and REEs are more abundant in the fine wastes from M'Dhilla-ZL (17.47%, 18.81%, 30.2 mg/kg, and 210.3 mg/kg, respectively), whereas higher contents in organic matter, Fe\({}_{2}\)O\({}_{3}\), and Al\({}_{2}\)O\({}_{3}\) characterize the sludge from Redeyef (3.89%, 5.97%, and 7.34%, respectively). It should be noted, however, that Cd, Cr, and Zn are more concentrated in the fine wastes of both laundries, as compared to their content in the raw phosphate. Batch experiments showed that, although the two fine waste samples of M'Dhilla-ZL and Redeyef laundries contain close total contents in Cd (26 mg/kg and 30.6 mg/kg, respectively); and U (30.2 mg/kg and 23 mg/kg, respectively), they behaved quite differently during the tests. With regards to pH conditions, the slightly alkaline conditions prevailed during the whole test. As a result, heavy metals are characterized by low mobility due to precipitation reactions, and the increase of adsorption sites is linked to OM (carboxyl groups), oxyhydrooxides, and clay minerals [55; 56], as well as the decrease of H\({}^{+}\) ions competition for adsorption [57]. Furthermore, the higher content in clay-phosphate fraction, clinoptiolite, and OM in the fine wastes of Redeyef (FW-R) seemed to have played a role in the retention of Cd, consequently, its low mobility with respect to Cd in the case of the equivalent sample from M'Dhilla-ZL (FW-ZL). Considering the sample FW-R, Cd could be associated with the phosphatic phase and adsorbed on the surface of silicate minerals (clays and clinoptiolite), which are plentiful in fine fractions. Besides aluminosilicates, these fine wastes contain also high amounts of OM (Table 3). Both of them are capable of adsorbing cadmium, consequently reducing its mobility [58], which makes it difficult to be released by leaching. Indeed, thanks to their very large specific surfaces (up to 800 m\({}^{2}\)/g) and their great cation-exchange capacities, organic matter and silicate minerals are believed to be excellent absorbents [59; 60; 61]. Clinoptiolite, with its cavernous structure, has a very high selective retention capacity for certain heavy metals, in particular Cd [62]. With regards to the sample FW-ZL, the significant mobility of Cd is attributed to its high content of phosphate and low content of silicate minerals, with high metal adsorption capacity. In freshwater, aqueous species of cadmium consist of Cd\({}^{2+}\), Cd(OH)\({}_{2}\)O\({}^{0}\) and CdHCO\({}_{3}\)\({}^{-}\)[63], among which Cd\({}^{2+}\) is the dominant ionic species up to pH 8 [64; 65; 66; 67], which is a free and very reactive (bioavailable) form [58; 68; 69; 70]. Likewise, the adsorption phenomenon by aluminosilicates and the carbonated nature of the two fine wastes may account for the small quantities of released uranium. As postulated by [PERSON] et al. [71], [PERSON] [29], [PERSON] et al. [72], [PERSON] et al. [73], and [PERSON] [32], an important part of uranium is adsorbed onto apatite in an oxidized form. According to [PERSON] [29] and [PERSON] et al.