Selective removal and long-term immobilization of uranium by ultralow content Fe0 in the pores of amino functionalized silica gel

[Display omitted] •Fe0@SGB-NH2 composites filled with semi-porous volume Fe0 were successfully prepared.•The content of Fe0 in Fe0@SGB-NH2 was only 1/28 times that of unmodified Fe0 to reach the same U(Ⅵ) removal rate.•Fe0@SGB-NH2 exhibited extraordinary selective capture and removal ability for uranium.•The sediment after the reaction of Fe0@SGB-NH2 and uranium exhibited excellent resistance to the risk of secondary release. Developing a materials to realize the selective adsorption and long-term immobilization of uranium is of great significance for the effective remediation of uranium-containing wastewater. Herein, we half-filled Fe0 into SGB-NH2 mesoporous channels to prepare a composite of Fe0 and amino-functionalized silica (Fe0@SGB-NH2), and used to the selective removal of uranium in solution under aerobic conditions. It was found that solutions containing 10 mg/L U(VI) could be purified 98.96% by Fe0@SGB-NH2 in the presence or absence of Na+, K+, Mg2+, SO42 −, NO3−, HCO3− and Cl− at pH 5–9. Compared with Fe0, its saturation magnetization decreased from 81.24 emu/g to 0.78 emu/g, while the specific surface area increased from 47.895 m2/g to 504.404 m2/g, successfully preventing the agglomeration and rapid corrosion of Fe0 without reducing its activity. More interestingly, the consumption of Fe0@SGB-NH2 was only 1/28 of untreated Fe0 when identical uranium removal efficiency was achieved. Further mechanistic studies indicated that U(VI) was firstly selectively captured by amino groups on the surface of the material and then reduction or adsorption in the pore, the long and narrow mesoporous channels reduce the possibility of uranium re-oxidation, thereby significantly reducing its re-release efficiency from 21.5% to only 1.73%. Encapsulation of Fe0 within SGB-NH2 channels was found to facilitate faster removal rate and higher U(VI) reduction ratio, and reduce uranium re-oxidation, thus benefit the long-term immobilization of uranium in contaminated groundwater.