Modeling and EXAFS investigation of U(VI) sequestration on Fe3O4/PCMs composites

Magnetite/porous carbonaceous materials (Fe3O4/PCMs) were synthesized simply by the hydrothermal method under nitrogen conditions. Various characterization, including scanning electron microscopy (SEM), X-ray diffraction spectra (XRD), Fourier transformed infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS), revealed that Fe3O4/PCMs composites contained plentiful oxygen-containing groups. The results of batch adsorption experiments displayed that U(VI) removal towards Fe3O4/PCMs composites was little influenced by ionic strength, revealing the inner-sphere complexation of U(VI) by Fe3O4/PCMs composites. The removal kinetics of U(VI) can be well fitted by the pseudo-second-order model. The maximum capture capacities of U(VI) on Fe3O4/PCMs reached 123.41 mg/g at 328 K. Moreover, the regeneration experiment showed that Fe3O4/PCMs composites exhibited good stability and recoverability for U(VI) capture. The capture mechanism of U(VI) on Fe3O4/PCMs involved adsorption and reduction by XPS and XANES investigation. In line with the EXAFS analysis, the U(VI) was partly reduced to U(IV) gradually with the increasing reaction time. The removal process of U(VI) on Fe3O4/PCMs composites was satisfactorily fitted by surface complexation modeling with an inner-sphere surface complexes. These results designated that Fe3O4/PCMs can be used as suitable adsorbents to eliminate uranium for environmental cleanup.