Extraction of Uranyl Ion Using 2-Thenoyltrifluoro Acetone (HTTA) in Room Temperature Ionic Liquids

Advancing Understanding of the +4 Metal Extractant Thenoyltrifluoroacetonate (TTA-); Synthesis and Structure of MIVTTA4 (MIV = Zr, Hf, Ce, Th, U, Np, Pu) and MIII(TTA)4- (MIII = Ce, Nd, Sm, Yb)

Thenoyltrifluoroacetone (HTTA)-based extractions represent popular methods for separating microscopic amounts of transuranic actinides (i.e., Np and Pu) from macroscopic actinide matrixes (e.g. bulk uranium). It is well-established that this procedure enables +4 actinides to be selectively removed from +3, + 5, and +6 f-elements. However, even highly skilled and well-trained researchers find this process complicated and (at times) unpredictable. It is difficult to improve the HTTA extraction-or find alternatives-because little is understood about why this separation works. Even the identities of the extracted species are unknown. In addressing this knowledge gap, we report here advances in fundamental understanding of the HTTA-based extraction. This effort included comparatively evaluating HTTA complexation with +4 and +3 metals (M^IV = Zr, Hf, Ce, Th, U, Np, and Pu vs M^III = Ce, Nd, Sm, and Yb). We observed +4 metals formed neutral complexes of the general formula M^IV(TTA)₄. Meanwhile, +3 metals formed anionic M^III(TTA)₄^- species. Characterization of these M(TTA)₄^x- ( x = 0, 1) compounds by UV-vis-NIR, IR, ¹H and ¹⁹F NMR, single-crystal X-ray diffraction, and X-ray absorption spectroscopy (both near-edge and extended fine structure) was critical for determining that Np^IV(TTA)₄ and Pu^IV(TTA)₄ were the primary species extracted by HTTA. Furthermore, this information lays the foundation to begin developing and understanding of why the HTTA extraction works so well. The data suggest that the solubility differences between M^IV(TTA)₄ and M^III(TTA)₄^- are likely a major contributor to the selectivity of HTTA extractions for +4 cations over +3 metals. Moreover, these results will enable future studies focused on explaining HTTA extractions preference for +4 cations, which increases from Np ^IV to Pu^IV, Hf^IV, and Zr^IV.

Highly efficient extraction and selective separation of uranium (VI) from transition metals using new class of undiluted ionic liquids based on H-phosphonate anions

In this paper, we report the development of an environmental friendly process to decontaminate uranium-containing ores and nuclear wastes by using non-fluorinated ionic liquids (ILs). The main advantages of this extraction process are the absence of any organic diluent and extra extraction agents added to the organic phase. Moreover, the process is cost-effective and maybe applied as a sustainable hydrometallurgical method to recover uranium. The distribution ratio (D_U) and the extraction efficiency (%E) of uranium(VI) (UO₂²⁺) were found to be dependent on the acidity of the aqueous phase, the extraction time, the alkyl chain length in the ILs, the concentration of the aqueous feed and molar quantity of ILs. The D_U value is higher than 600 and the %E is equal to 98.6% when [HNO₃]=7M. The extraction reactions follows a neutral partition or ionic exchange mechanism depending on nitric acid concentration. The nature of bonding in the extracted complexes was investigated by spectroscopic techniques. The potential use of Mor_1-8-OP for the separation of UO₂²⁺ from a mixture containing transition metal ions Mⁿ⁺ was also examined. The UO₂²⁺ ions were separated and extracted efficiently. These ILs are promising candidates for the recovery and separation of uranium.

U(VI) Extraction by 8-hydroxyquinoline: a comparison study in ionic liquid and in dichloromethane

Room temperature ionic liquids (RTILs) represent a recent new class of solvents with potential application in liquid/liquid extraction based nuclear fuel reprocessing due to their unique physical and chemical properties. The work herein provides a comparison of U(VI) extraction by 8-hydroxyquinoline (HOX) in a commonly used RTIL, i.e. 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) and in conventional solvent, i.e. dichloromethane (CH2Cl2). The effect of HOX concentration, solution acidity and nitrate ions on the extraction were discussed in detail, and the speciation analyses of the extracted U(VI) were performed. One of the main emphasis of this work is the extraction mechanism of U(VI) extracted from aqueous phase into RTILs and conventional solvent. In CH2Cl2, the extraction occurs through a combination of ion change and neutral complexation, and the extracted complex is proposed as UO2(OX)2HOX. In [C4mim][PF6], although a cation-change mechanism as previously reported for RTILs-based system was involved, the extracted complex of UO2(OX)1.5(HOX)1.5(PF6)0.5 gave a clear indication that the usage of HOX as an acidic extractant markedly inhibited the solubility loss of [C4mim][PF6] during the extraction by leaching H+ to aqueous phase. Moreover, the extracted U(VI) in [C4mim][PF6] can be easily stripped by using 0.01 M nitric acid, which provides a simple way of the ionic liquid recycling.

Actinide ion extraction using room temperature ionic liquids: opportunities and challenges for nuclear fuel cycle applications

Studies on the extraction of actinide ions from radioactive wastes have great relevance in nuclear fuel cycle activities, mainly in the back end processes focused on reprocessing and waste management.

Combined effect of ether and siloxane substituents on imidazolium ionic liquids

The combined effect of ether and siloxane substituents on imidazolium cations helps overcome the Coulombic attraction, van der Waals forces, size factor and conformational degree of freedom, and exerts an impact on viscosity, density and thermal properties of ionic liquids.