Selective Dissolution of Oxides of Uranium in Ionic Liquid with Subsequent Electrodeposition: Exploring Sustainable Nonaqueous Processing

The present study reports the acid-free, ligand-free, fast room-temperature dissolution of UO₃ in an ionic liquid (C₄mimPF₆: 1-butyl-3-methylimidazolium hexafluorophosphate) with subsequent electrodeposition, demonstrating the feasibility of sustainable, environmentally benign, nonaqueous processing of uranium trioxide under chemically and thermally mild conditions via in situ fluoride generation. The solubility of uranium oxides follows the trend UO₃ > U₃O₈ > UO₂. The endothermic behavior of the dissolution was confirmed through calorimetric investigation. The dissolution of UO₃ followed pseudo-first-order behavior, with an activation energy of ∼52.2 kJ mol⁻¹. Only 2 h was required to achieve the quantitative and selective dissolution of UO₃, resulting in a solution of concentration 5 mg/mL with separation factors in the range of 3.1 × 10²-6.9 × 10² with respect to trivalent lanthanide oxides and 2.3 × 10³-6.9 × 10³ with respect to CuO and Pr₆O₁₁. The cyclic voltamogram exhibited a single reduction peak at -0.6 V, indicating the reduction of uranium from (VI) to (V); however, no analogous oxidation peaks in the anodic sweep were observed, revealing irreversible redox behavior. The dissolved uranium was electrochemically recovered from the ionic liquid phase onto a copper plate, resulting in a black deposit of UO₂, as confirmed by XRD, EDXRF, and FTIR analyses.