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. [ABSTRACT FROM AUTHOR]