Abstract
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•Magnetic chitosan micro-particles efficiently grafted with amine and dithizone.•Uranyl sorption increases by functionalization (i.e., diethylenetriamine amine).•Ultrasonic treatment (frequency: 80 kHz) drastically increases mass transfer.•Microwave speeds up sorption but drastically reduces sorption capacity.•Metal desorption is greatly enhanced by short microwave exposure.
Magnetic chitosan nanoparticles, activated by glycidyl methacrylate, can be functionalized by grafting diethylenetriamine (DETA) and dithizone for improving U(VI) sorption at pH around 5. The physicochemical properties of the materials have been characterized by a wide variety of analytical techniques. Uranyl sorption increases with the pH (progressive deprotonation of amine and sulfur groups). Uptake kinetics are controlled by the agitation mode: the equilibrium time is reduced while using ultrasonic treatment (especially at highest frequency: 80 kHz): the cavitation effect improves the accessibility to internal reactive groups (sorption capacity is increased). The diffusivity coefficient is increased by 4–5 times. In the case of microwave, the sorption capacity is significantly reduced (especially for R-Dithizone, down to 0.8 mmol U g−1) because of temperature increase, which limits the sorption (exothermic mechanism). Mass transfer is tremendously enhanced: equilibrium time is less than 60 s (30 min for ultrasonic treatment and 120 min with mechanical agitation). Sorption capacity at monolayer saturation (Langmuir) decreases with increasing the temperature from 2.20 to 1.74 mmol U g−1 for R-Amine (from 1.77 to 1.22 mmol U g−1 for R-Dithizone). The sorption enthalpy is close to −19.7 kJ mol−1 for R-Amine (with positive entropy change, ΔS°) and −34.2 kJ mol−1 for R-Dithizone (negative ΔS°). Metal desorption is highly efficient using 0.3 M Na2CO3/0.1 M H2O2solution. Metal desorption is instantaneous (less than 1 min) and complete when using microwave treatment. The ultrasonic treatment allows improving desorption efficiency and decreasing the concentration of the eluent compared with mechanical agitation. The process is successfully applied for uranyl separation from the leachates of marine sediments, especially in the presence of Complexon III (masking agent).