Removal Of Uranium(Ⅵ) Using Organic Functionalized Mesoporous Silica As Adsorbents

Uranium is one of main radioelements in the nuclear industry, where it starts as a source and ends up as a final waste component. Meanwhile, uranium is one of the most important heavy metals with chemical toxicity and radioactivity, which causes progressive or irreversible renal injury and its compounds are potential carcinogens. Therefore, the demand of a valid method to remove uranium from wastewater and radioactive waste is greatly urgent. Until now, many methods have been taken into account. Among them, the sorption offers benefits of simplicity, rapidity, and easy recycling.Five different functional SBA-15were prepared by post-grafting method using three iminodiacetic acid derivatives (SBA-15-ethylenediaminetriacetic acid (SBA-15-ED3A), SBA-15-diethylenetriaminetetraacetic acid (SBA-15-DT4A) and SBA-15-1,2-cyclohexylene-dinitrilotriacetic acid (SBA-15-CyD3A)) and two phosphonate derivatives SBA-15-diethylethyl-phosphonate ((SBA-15-DEP) and SBA-ethylphosphonic acid (SBA-15-PA)), which were characterized by FT-IR,13C CP-MAS NMR, TEM, nitrogen adsorption/desorption experiments, and elemental analysis. These results confirmed that of SBA-15was successful modified.These materials were used as adsorbents for removal of uranium(Ⅵ) from aqueous solution. The effect of pH, ionic strength, contact time, solid-liquid ratio, initial metal ion concentration, temperature, and coexistent ions on uranium(Ⅵ) sorption behaviors of the functionalized SBA-15was studied by a batch method. Typical sorption isotherms (Langmuir and Freundlich) and sorption kinetics (pseudo first-order and pseudo second-order models) were determined for sorption process, related parameters were calculated. The results are as follows:(1) Removal of uranium(Ⅵ) from aqueous solution using iminodiacetic acid derivatives functionalized SBA-15as adsorbents.The results show that the sorption ability of pure SBA-15for U(Ⅵ) were obviously increased after the functionalization, the U(Ⅵ) sorption ability before and after the modification is strongly dependent on pH values, and inner-sphere complexation may be the main sorption mechanism of U(VI). The sorption process was found to follow pseudo-second-order type sorption kinetics for all materials. For modified SBA-15, the sorption isotherm has been successfully modeled by the Langmuir isotherm, but Freundlich isotherm is better for pure SBA-15. SBA-15-ED3A and. SBA-15-DT4A have similar sorption properties under all conditions because of similar structural characteristics. The organic groups on SBA-15-CyD3A surface display lower sorption capacity for U(Ⅵ) than SBA-15-ED3A and SBA-15-DT4A, but showed the highest selectivity for U(Ⅵ) over a range of competing metal ions because of the spatial configuration, and it may has potential application prospect in U(Ⅵ) separation area.(2) Removal of uranium(Ⅵ) from aqueous solution using phosphonate derivatives functionalized SBA-15as adsorbents. U(Ⅵ) sorption ability of all adsorbents is strongly dependent on pH values, and inner-sphere complexation may be the main sorption mechanism of U(Ⅵ). The sorption isotherm has been successfully modeled by the Langmuir isotherm, which reveals a monolayer chemical sorption of U(Ⅵ) on modified SBA-15, but Freundlich isotherm is better for SBA-15, it indicates that different sites with several sorption energies are involved. SBA-15-PA showed not only a good sorption ability and a desirable selectivity for U(Ⅵ) over a range of competing metal ions, but also a excellent reusability, which had potential application in separation of uranium(Ⅵ).