Role of Phase Modifiers in Controlling the Third-phase Formation During the Solvent Extraction of Trivalent Actinides

Metastable precipitation and ion-extractant transport in liquid-liquid separations of trivalent elements

The extractant-assisted transport of metal ions from aqueous to organic environments by liquid-liquid extraction has been widely used to separate and recover critical elements on an industrial scale. While current efforts focus on designing better extractants and optimizing process conditions, the mechanism that underlies ionic transport remains poorly understood. Here, we report a nonequilibrium process in the bulk aqueous phase that influences interfacial ion transport: the formation of metastable ion-extractant precipitates away from the liquid-liquid interface, separated from it by a depletion region without precipitates. Although the precipitate is soluble in the organic phase, the depletion region separates the two and ions are sequestered in a long-lived metastable state. Since precipitation removes extractants from the aqueous phase, even extractants that are sparingly soluble in water will continue to be withdrawn from the organic phase to feed the aqueous precipitation process. Solute concentrations in both phases and the aqueous pH influence the temporal evolution of the process and ionic partitioning between the precipitate and organic phase. Aqueous ion-extractant precipitation during liquid-liquid extraction provides a reaction path that can influence the extraction kinetics, which plays an important role in designing advanced processes to separate rare earths and other minerals.

Small Cyclic Diglycolamides: Tautomerism, Solvent Extraction and Coordination with f-Elements: One Strain to Rule Them All

The search for new effective extractants is an important task for the management of high-level liquid waste (HLW) generated during the reprocessing of spent nuclear fuel. Here, we synthesized a series of diglycolamides with cyclic substituents for the first time. We disclosed their coordination with f-element nitrates [La(NO3)3 and UO2(NO3)2] by SC-XRD study and complexation properties toward Am(III), Ln(III), and U(VI) during solvent extraction from nitric acid solutions. Using dynamic nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations, the importance of tautomerism in the extraction properties of diglycolamides was shown.

Ligand Effect on Physicochemical Properties of Ionic Liquid

In the solvent extraction process, the importance of an extractant (or ligand) and a diluent is inferred from their respective physicochemical properties. We have brought together all the recent results reported on the mixture of different extractants dissolved in a well-known ionic liquid diluent: 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₄ mim][NTf₂ ]) in the form of a review and aimed to emphasize the role of ligand polarity and structure on the physicochemical properties of an ionic liquid (IL) diluent. Some of the most important properties such as dynamic viscosity (η), absolute density ( ρ ${{\rm{{\rm \rho} }}}$ ), energy of activation (E_a ), coefficient of thermal expansion (α), phase separation time (PST), refractive index (n), etc., have been discussed meticulously in the paper. The effect of ligand structure on the aggregation behaviour of IL phase and the physicochemical properties of gamma irradiated solvent phases containing different ligands and their solution with IL phase also have been deliberated in detail.

Modulating Aggregation in Microemulsions: The Dispersion by Competitive Intermolecular Interaction Model

A phenomenological model has been developed for the mechanism of action of phase modifiers as additives that control aggregation phenomena within water-in-oil emulsions. The "Dispersion by Competitive Intermolecular Interaction" model (DCI) explicitly considers the strength and prevalence of different intermolecular interactions that influence the molecular association of amphiphiles, the resulting distribution of aggregate size, and interaggregate interactions that influence phase phenomena. The existing "cosolvent" and "cosurfactant" association models, which describe the distribution of these amphiphiles within the solution, are re-examined in the context of intermolecular interactions. The different contributions of intermolecular interactions to the potential energy landscape of molecular association create distinct regimes within the DCI model that explain prior observations of cosolvent and cosurfactant behavior. The specific system under consideration, the N,N,N^',N'-tetraoctyl diglycolamide amphiphile extractant with tributyl phosphate or dihexyl octanamide phase modifier additives, represents a new regime-labeled the polar disruption regime-where strong hydrogen bonding of the phase modifier with the polar-solutes disrupts the internal hydrogen bonding network of the polar micellar core, thereby decreasing aggregate size and narrowing the polydispersity in solution.

Study on the extraction of lanthanides by isomeric diglycolamide extractants: an experimental and theoretical study

Two isomeric diglycolamide (DGA) extractants, N,N'-dimethyl-N,N'-dioctyl diglycolamide (LI) and N,N-dimethyl-N',N'-dioctyl diglycolamide (LII), were used to perform a comparative study on the extraction performances towards several lanthanides by extraction experiments and theoretical calculations. The experimental results show that both LI and LII show a positive sequence on the extraction of lanthanides, and LI exhibits the higher complex ability with these lanthanides than LII, except for La and Ce. Slope analysis shows that 1:2 or 1:3 complexes are formed between the two ligands and the metal ions. The geometrical structures of the complexes were optimized in the gas phase by density functional theory (DFT) on the basis of complex compositions. The results of bond lengths, MBOs and topological analysis indicated that the electrostatic interaction between metal ions and two amide O atoms in the LII ligand is not as homogeneous as in LI, and this inhomogeneity is likely to be related to the poor extraction performance of LII.

Nonaqueous Solvent Extraction for Enhanced Metal Separations: Concept, Systems, and Mechanisms

Efficient and sustainable separation of metals is gaining increasing attention, because of the essential roles of many metals in sustainable technologies for a climate-neutral society, such as rare earths in permanent magnets and cobalt, nickel, and manganese in the cathode materials of lithium-ion batteries. The separation and purification of metals by conventional solvent extraction (SX) systems, which consist of an organic phase and an aqueous phase, has limitations. By replacing the aqueous phase with other polar solvents, either polar molecular organic solvents or ionic solvents, nonaqueous solvent extraction (NASX) largely expands the scope of SX, since differences in solvation of metal ions lead to different distribution behaviors. This Review emphasizes enhanced metal extraction and remarkable metal separations observed in NASX systems and discusses the effects of polar solvents on the extraction mechanisms according to the type of polar solvents and the type of extractants. Furthermore, the considerable effects of the addition of water and complexing agents on metal separations in terms of metal ion solvation and speciation are highlighted. Efforts to integrate NASX into metallurgical flowsheets and to develop closed-loop solvometallurgical processes are also discussed. This Review aims to construct a framework of NASX on which many more studies on this topic, both fundamental and applied, can be built.

Extraction of total antioxidants from Azadirachta indica (neem) using three phase partitioning and its process intensification using ultrasound

The majority of the naturally occurring antioxidants are obtained from plant sources. The antioxidant activity is mostly exhibited by polyphenols present in the plant cells. Azadirachta Indica (Neem) leaves are renowned for their medicinal applications due to their anti-inflammatory, antimalarial, antifungal, antibacterial, antiviral, antioxidant, and anticarcinogenic properties. This work aims to optimize the extraction of Azadirachta Indica (Neem) leaf antioxidants using three-phase partitioning (TPP). The optimized conditions are operating time 15 minutes, slurry ratio 1:30 (g/mL), salt concentration 30% (w/v), aqueous to solvent ratio 1:1.5 (v/v), and stirring speed 400 rpm that infer 74.66% extraction yield. Additionally, ultrasonic pretreatment was also employed to increase the extraction yield up to 86.61%. Sonication pretreatment for 4 min operated at 30 W power, and 75% duty cycle was observed to offer maximum antioxidant extraction about 3.3 mg/g.

Role of diluent in the unusual extraction of Am3+ and Eu3+ ions with benzene-centered tripodal diglycolamides: local structure studies using luminescence spectroscopy and XAS

Two benzene-centered tripodal DGA ligands (LI and LII) were used for the extraction of Am3+/Eu3+ from HNO3 medium into n-dodecane modified with various amounts of isodecanol. Luminescence spectroscopy and EXAFS studies were carried out for structural information.