Hydration counteracts the separation of lanthanides by solvent extraction.
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ABSTRACT:
SUBMITTER: Li Z
PROVIDER: S-EPMC9285791 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Partitioning of americium from lanthanides (Ln) present in used nuclear fuel plays a key role in the sustainable development of nuclear energy1-3. This task is extremely challenging because thermodynamically stable Am(III) and Ln(III) ions have nearly identical ionic radii and coordination chemistry. Oxidization of Am(III) to Am(VI) produces AmO22+ ions distinct with Ln(III) ions, which has the potential to facilitate separations in principle. However, the rapid reduction of Am(VI) back to Am(III) by radiolysis products and organic reagents required for the traditional separation protocols including solvent and solid extractions hampers practical redox-based separations. Herein, we report a nanoscale polyoxometalate (POM) cluster with a vacancy site compatible with the selective coordination of hexavalent actinides (238U, 237Np, 242Pu and 243Am) over trivalent lanthanides in nitric acid media. To our knowledge, this cluster is the most stable Am(VI) species in aqueous media observed so far. Ultrafiltration-based separation of nanoscale Am(VI)-POM clusters from hydrated lanthanide ions by commercially available, fine-pored membranes enables the development of a once-through americium/lanthanide separation strategy that is highly efficient and rapid, does not involve any organic components and requires minimal energy input.
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Project description:Solvent extraction is used widely for chemical separations and environmental remediation. Although the kinetics and efficiency of this process rely upon the formation of ion-extractant complexes, it has proven challenging to identify the location of ion-extractant complexation within the solution and its impact on the separation. Here, we use tensiometry and X-ray scattering to characterize the surface of aqueous solutions of lanthanide chlorides and the water-soluble extractant bis(2-ethylhexyl) phosphoric acid (HDEHP), in the absence of a coexisting organic solvent. These studies restrict ion-extractant interactions to the aqueous phase and its liquid-vapor interface, allowing us to explore the consequences that one or the other is the location of ion-extractant complexation. Unexpectedly, we find that light lanthanides preferentially occupy the liquid-vapor interface. This contradicts our expectation that heavy lanthanides should have a higher interfacial density since they are preferentially extracted by HDEHP in solvent extraction processes. These results reveal the antagonistic role played by ion-extractant complexation within the aqueous phase and clarify the advantages of complexation at the interface. Extractants in common use are often soluble in water, in addition to their organic phase solubility, and similar effects to those described here are expected to be relevant to a variety of separations processes.
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Project description:A DGA-arm-grafted macrocyclic aza-crown ether ligand (Cr6DGA) was synthesized, and its solvent extraction behavior toward trivalent americium and europium in nitric acid medium was studied. The effects of various parameters such as the contact time, temperature, concentration of the extractant, and acidity on the extraction by Cr6DGA were investigated. It was found that in 3 mol/L HNO3, the SFEu/Am value was about 2. The complexation energies calculated by DFT showed that the Eu(III) complexes were more stable than the corresponding Am(III) complexes in gas, aqueous, and organic phases. Furthermore, the coordination study showed that the metal/ligand ratio of the extracted species was 1:2 by mass spectrometry (MS) analysis. The time-resolved laser-induced fluorescence spectra (TRLFS) further proved that the extracted species contained one water molecule, and so the composition of the extracted complexes may be [EuL2NO3(H2O)]2+ or [EuL2(NO3)2(H2O)]+. Finally, DFT calculations revealed that [EuL2(NO3)2(H2O)]+ is a more stable species and the binding energy of Eu(III) with the DGA unit is lower than that with the crown unit.
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Project description:Lanthanides (Ln) are critical raw materials, however, their mining and purification have a considerable negative environmental impact and sustainable recycling and separation strategies for these elements are needed. In this study, the precipitation and solubility behavior of Ln complexes with pyrroloquinoline quinone (PQQ), the cofactor of recently discovered lanthanide (Ln) dependent methanol dehydrogenase (MDH) enzymes, is presented. In this context, the molecular structure of a biorelevant europium PQQ complex was for the first time elucidated outside a protein environment. The complex crystallizes as an inversion symmetric dimer, Eu2 PQQ2 , with binding of Eu in the biologically relevant pocket of PQQ. LnPQQ and Ln1Ln2PQQ complexes were characterized by using inductively coupled plasma mass spectrometry (ICP-MS), infrared (IR) spectroscopy, 151 Eu-Mössbauer spectroscopy, X-ray total scattering, and extended X-ray absorption fine structure (EXAFS). It is shown that a natural enzymatic cofactor is capable to achieve separation by precipitation of the notoriously similar, and thus difficult to separate, lanthanides to some extent.
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Project description:We report on the separation and recovery of scandium(III) from sulfate solutions using solvent extraction and a membrane transport system utilizing newly synthesized amic acid extractants. Scandium(III) was quantitatively extracted with 50 mmol dm-3 N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) or N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]phenylalanine (D2EHAF) in n-dodecane at pH 2 and easily stripped using a 0.5 mol dm-3 sulfuric acid solution. The extraction mechanisms of scandium(III) extraction with D2EHAG and D2EHAF were examined, and it was established that scandium(III) formed a 1:3 complex with both extractants (HR), that is, Sc(SO4)2 - aq + 1.5(HR)2org ⇄ Sc(SO4)R(HR)2org + H+ aq + SO4 2- aq. The equilibrium constants of extraction were evaluated to be 4.87 and 9.99 (mol dm-3)0.5 for D2EHAG and D2EHAF, respectively. D2EHAG and D2EHAF preferentially extracted scandium(III) with a high selectivity compared to common transition metal ions under high acidic conditions (0 < pH ≤ 3). In addition, scandium(III) was quantitatively transported from a feed solution into a 0.5 mol dm-3 sulfuric acid receiving solution through a polymer inclusion membrane (PIM) containing D2EHAF as a carrier. Scandium(III) was completely separated thermodynamically from nickel(II), aluminum(III), cobalt(II), manganese(II), chromium(III), calcium(II), and magnesium(II), and partially separated from iron(III) kinetically using a PIM containing D2EHAF as a carrier. The initial flux value for scandium(III) (J 0,Sc = 1.9 × 10-7 mol m-2 s-1) was two times higher than that of iron(III) (J 0,Fe = 9.3 × 10-8 mol m-2 s-1).
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Project description:Recovery of platinum group metals from spent materials is becoming increasingly relevant due to the high value of these metals and their progressive depletion. In recent years, there is an increased interest in developing alternative and more environmentally benign processes for the recovery of platinum group metals, in line with the increased focus on a sustainable future. To this end, ionic liquids are increasingly investigated as promising candidates that can replace state-of-the-art approaches. Specifically, phosphonium-based ionic liquids have been extensively investigated for the extraction and separation of platinum group metals. In this paper, we present the extraction capacity of several phosphonium-based ionic liquids for platinum group metals from model deep eutectic solvent-based acidic solutions. The most promising candidates, P66614Cl and P66614B2EHP, which exhibited the ability to extract Pt, Pd, and Rh quantitively from a mixed model solution, were additionally evaluated for their capacity to recover these metals from a spent car catalyst previously leached into a choline-based deep eutectic solvent. Specifically, P66614Cl afforded extraction of the three target precious metals from the leachate, while their partial separation from the interfering Al was also achieved since a significant amount (approx. 80%) remained in the leachate.
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