Retention of Toxic Metal in Solution by Marl Treated by Heat at Different Temperatures

In this study, two marl samples recovered from the bedrock of the Draria Nuclear Research Centers site aquifer (CRND) were heat-treated in an oven at 200°C and 400°C for four hours. This treatment was carried out to study its effect on the retention capacity of MPM-200 and MPM-400 samples when treated with a solution containing Uranium. The marl samples were characterized by X-Ray Fluorescence (XRF), Brunauer–Emmett–Teller (BET), particle size distribution and FTIR analysis. The elemental XRF analysis shows that the major compounds are Silica, Calcium, Aluminum, Iron and Potassium. BET analysis established the predominance of the meso-porous character associated with a specific surface area value equal to 17.55 m²/g for MPM-200 and 17.88 m²/g for MPM-400. The results of the particle size analysis of the MPM-200 and MPM-400 samples show that the heat treatment of our marl samples did not affect their particle sizes. The heat treatment applied to the marl samples caused a slight progressive decrease in the intensity of the FTIR transmittance band signal for both samples MPM200 and MPM400 compared to the signal obtained for the raw marl. The various adsorption experiments were monitored by varying the mass of adsorbent, the volume of solution, the contact time, the initial pH, the initial Uranium concentration and the stirring speed. An optimum adsorption capacity (3.5 mg/g for MPM-200 and 2.8 mg/g for MPM-400) was obtained after 60 min with a sample mass of 80 mg, a volume of 30 ml, an initial solution concentration of 10 mg/L, an initial pH equal to 2 and a stirring speed of 180 rpm. The kinetics of Uranium adsorption by our MPM-200 and MPM-400 adsorbents follow the pseudo-second-order model, with a coefficient of determination R²=0.9782 for MPM-200 and R²=0.9977 for MPM-400. The diffusion process is controlled simultaneously by intra-particle diffusion and liquid film diffusion. The isotherm with the best correlation for MPM-200 is the Freundlish model, followed by the Sips model and finally the two Langmuir and Toth models. For MPM-400, the best model is Sips, followed by Toth, then Langmuir and finally Freundlish, but with very little difference in the values obtained for R², R²_adj. The thermodynamic study revealed that the process of Uranium adsorption by MPM-200 and MPM-400 is thermodynamically feasible, spontaneous, and endothermic, with the existence of a slight order.