High capacity amidic succinic acid functionalized mesoporous silica for the adsorption of uranium

The nuclear reactors operating worldwide are currently using the uranium mined from the resources available on the earth's crust. A significant volume of aqueous waste containing a small quantity of uranium was generated during the processing of ores. There is a growing demand to remove this toxic uranium from these aqueous streams, owing to the limit of tolerable daily intake (15 μg L⁻¹) for uranium imposed by the World Health Organization. This demand throws huge challenges to the separation chemists to engineer the solid phase adsorbents having high capacity, excellent selectivity and satisfactory throughputs for processing a vast quantity of aqueous waste containing traces of uranium. In this context, the task specific amidic succinic acid (SUC) functional groups tailored on mesoporous silica having wide porosity and large surface area have been prepared and characterized by BET surface area, pore and particle size distribution, thermogravimetry, SEM-EDX analysis, FT-IR and Raman spectroscopy. The adsorption behavior of uranium (VI) from the aqueous phase on the tailored adsorbent (MCM-SUC) was studied as a function of pH of the aqueous phase, duration of equilibration, uranium concentration in the aqueous phase, and the results were compared with the adsorbent containing the same functional group but grafted on silica gel (Si-SUC), which exhibited adsorption capacity of 61 mg g⁻¹. The fast kinetics of adsorption and significantly high Langmuir adsorption capacity of uranium (807 mgg ⁻¹), as compared to the other mesoporous adsorbents reported in literature, achieved in MCM-SUC was due to controlled synthesis of SUC functionalized mesoporous silica that favoured high degree of SUC number density on the mesoporous material. The adsorbed uranium was recovered using 0.1 M nitric acid.