Efficient adsorption of uranyl ions from aqueous solution by Gd2O3 and Gd2O3–MgO composite materials

In this work, pure gadolinium oxide (Gd2O3) and mixed gadolinium oxide (Gd2O3)–magnesium oxide (MgO) composites were synthesized by simple hydrothermal method and calcination treatment. Two kinds of materials were used to remove uranyl ions from aqueous solution and characterized the structure and morphology by means of XRD, FT-IR, SEM, EDS and XPS. MgO was introduced into Gd2O3 material, which effectively avoided the agglomeration of Gd2O3 material and increased the adsorption capacity. The effects of different initial pH, initial uranium concentration and contact time on the adsorption performance of UO22+ were investigated by static adsorption experiments. At 25 °C, the maximum adsorption capacities of Gd2O3 and Gd2O3–MgO for UO22+ were 473.43 mg·g−1 and 812.41 mg·g−1, respectively. The adsorption process was fitted well with the Langmuir isotherm model and pseudo-second-order kinetic model. The thermodynamic fitting parameters (ΔG < 0, ΔS > 0 and ΔH > 0) indicated that the adsorption properties are endothermic and spontaneous. Gd2O3–MgO has a relatively large specific surface area and high adsorption capacity, but its stability and regeneration ability are reduced after three times of reuse. The possible adsorption mechanism is derived from XPS and FT-IR analysis, which mainly involves the complexation of –OH and U(VI) generated by the hydration on the surface of the materials.