Liquid-liquid extraction of Pu(IV), U(VI) and Am(III) using malonamide in room temperature ionic liquid as diluent

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.

Substituent Effect on the Selective Separation and Complexation of Trivalent Americium and Lanthanides by N,O-Hybrid 2,9-Diamide-1,10-phenanthroline Ligands in Ionic Liquid

The extraction and complexation of trivalent americium (Am) and lanthanides (Ln) by four 2,9-diamide-1,10-phenanthroline (DAPhen) ligands with different alkyl substituent groups on the diamide moiety in an ionic liquid (IL), C₄mimNTf₂, were studied through a combination of batch extraction, spectroscopic, and calorimetric approaches. All four DAPhen ligands can achieve selective separation of Am(III) from Eu(III), but the detailed extractability and the extraction kinetics are affected significantly by the length of the alkyl substituent groups. UV-vis absorption spectrophotometric titrations indicate that Ln(III) coordinates with all four ligands in a 1:2 mode in the ionic liquid and the binding strength decreases with the increase of the alkyl chain length. The complexation of the DAPhen ligands with Ln(III) in the ionic liquid is driven by highly positive entropies and opposed by endothermic enthalpies. A luminescence spectroscopy study suggests that each DAPhen ligand coordinates in a tetradentate form with Eu(III). This work further unravels the unique extraction and coordination behavior in an ionic liquid system and offers additional guidelines to design more efficient DAPhen ligands for Ln(III)/An(III) separation.

Reduced Graphene Oxide/ZIF-67 Aerogel Composite Material for Uranium Adsorption in Aqueous Solutions

Safe and sustainable development of the nuclear industry has become the focus of attention, so it is important to manage byproducts of radioactive elements, such as uranium, which is inevitably discharged into water bodies. In this work, an adsorbent was fabricated by the in-site assembly of zeolitic imidazolate framework-67 (ZIF-67) on reduced graphene oxide (rGO) hydrogel. The adsorption property of the rGO/ZIF-67 aerogel toward U(VI) was studied via batch adsorption experiment. According to kinetic fitting tests, the adsorption property was in accord well with the pseudo-second-order model, revealing that the adsorption process was chemisorption; the results of the isothermal model conform to the Langmuir model, which exhibited an excellent adsorption capacity of 1888.55 mg/g. The thermodynamic parameter (ΔH° = 11.7 kJ/mol) obtained from the experimental data demonstrated that temperature rise is favorable for the adsorption. Based on the characterization of the material and results of the adsorption, the adsorption mechanism for U(VI) may be explained by surface complexation and electrostatic attraction. In general, all these results and characteristics of the adsorbent show that the rGO/ZIF-67 aerogel provides an alternative way to fabricate novel uranium adsorbent.

The targeted design of dual-functional metal–organic frameworks (DF-MOFs) as highly efficient adsorbents for Hg2+ ions: synthesis for purpose

Designing adsorbents with accessible chelating sites and achieving high contaminant purification efficiency are still important to overcome environmental remediation challenges.

Graphene-synergized 2D covalent organic framework for adsorption: A mutual promotion strategy to achieve stabilization and functionalization simultaneously

Most of current absorbents are difficult to hold favorable stability and functionality simultaneously when used in condition of high acidity and strong radiation existing in nuclear industry. Herein, a new graphene-synergized 2D covalent organic framework (GS-COF) was obtained via an in-situ loading of a covalent organic framework (TDCOF) on graphene sheets based on a mutual promotion strategy proposed in this work. The corresponding oximation products, o-GS-COF, and also o-TDCOF as a reference object, were respectively prepared subsequently. The results of experiments confirmed that o-GS-COF possesses better acid and irradiation stability than that of o-TDCOF. Adsorption experiments showed that the adsorption capacity of o-GS-COF for uranium is 144.2 mg g^-1, higher than that of GO (92.5 mg g^-1) and o-TDCOF (105.0 mg g^-1), and the maximum adsorption capacity reaches 220.1 mg g^-1. In the multi-ions system, o-GS-COF also displayed good selective adsorption property for uranium with SF_U/M 35-100 for 5 coexisting divalent metal ions and 14-18 for 5 coexisting trivalent lanthanide ions. The proposed strategy successfully achieved the synergistic improvement of both stability and functionality for the desired adsorbing materials and is of considerable practical utility in the field of design and preparation of reliable high-performance absorbents.

Unique reversibility in extraction mechanism of U compared to solvent extraction for sorption of U(VI) and Pu(IV) by a novel solvent impregnated resin containing trialkyl phosphine oxide functionalized ionic liquid

Novel Solvent Impregnated Resin (SIR) material was prepared by impregnating a trialkyl phosphine oxide functionalized ionic liquid (IL) into an inert polymeric material XAD-7. A series of SIR materials were prepared by varying the IL quantity. Sorption of both U(VI) and Pu(IV) were found to increase with increasing IL concentration in SIR up to an optimum IL concentration of 435 mg g^-1 of SIR beyond which no effect of IL concentration was observed. A change of mechanism of sorption for U(VI) by SIR was observed in comparison to solvent extraction. The dependency of U(VI) sorption with nitric acid concentration showed a reverse trend compared to solvent extraction studies while for Pu(IV) the trend remained same as observed with solvent extraction. Sorption of both the radionuclides was found to follow pseudo second order mechanism and Langmuir adsorption isotherm. Distribution co-efficient measurements on IL impregnated SIR showed highly selective sorption of U(VI) and Pu(IV) over other trivalent f-elements and fission products from nitric acid medium.

Extraction of plutonium(IV) by diglycolamide extractants in room temperature ionic liquids

Extraction of Pu(IV) was investigated using solutions of two diglycolamide extractants viz., N,N,N′,N′-tetra-n-octyldiglycolamide (TODGA) and its branched homolog, N,N,N′,N′-tetra(2-ethylhexyl) diglycolamide (T2EHDGA), dissolved in two imidazolium based room temperature ionic liquids viz., 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C4mim][NTf2]) and 1-octyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide ([C8mim][NTf2]) from aqueous nitric acid medium. The extraction kinetics was found to be extremely slow which is reported for the first time for analogous extraction systems and took as long as 30 h to attain equilibrium D Pu values. In general, TODGA based solvents showed better extraction of Pu(IV) than the T2EHDGA based solvents, one order of magnitude higher, and though both the ionic liquids ultimately yielded comparable D Pu values, attainment of equilibrium was slower with [C4mim][NTf2]. The extracted species conformed to 1:1 for TODGA in both the ionic liquids while a mixture of 1:1 and 1:2 species was observed for T2EHDGA at 1 M HNO3 which changed to 1:1 species at 4 M HNO3. The extracted species is proposed to be (Pu(L)x 4+)IL (where, L is the extractant and x=1 or 2) at lower acidities suggesting a cation exchange mechanism which changes over to (Pu(NO3)4⋅L)IL at 4 M HNO3 conforming to a solvation mechanism for all the systems except for T2EHDGA-[C8mim][NTf2]. UV-VIS spectroscopic studies were carried out to throw light on the nature of the extracted species.

Uranium biosorption from aqueous solution by the submerged aquatic plant Hydrilla verticillata

The biosorption characteristics of U(VI) from aqueous solution onto a nonliving aquatic macrophyte, Hydrilla verticillata (dry powder), were investigated under various experimental conditions by using batch methods. Results showed that the adsorption reached equilibrium within 60 min and the experimental data were well fitted by the pseudo-first-order kinetic model. U(VI) adsorption was strongly pH dependent, and the optimum pH for U(VI) removal was 5.5. Isotherm adsorption data displayed good correlation with the Langmuir model, with a maximum monolayer adsorption capacity of 171.52 mg/g. Thermodynamic studies suggested that U(VI) adsorption onto H. verticillata was an exothermic and spontaneous process in nature. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that the amino and hydroxyl groups on the algal surface played an important role in U(VI) adsorption. The mechanisms responsible for U(VI) adsorption could involve electrostatic attraction and ion exchange. In conclusion, H. verticillata biomass showed good potential as an adsorption material for the removal of uranium contaminants in aqueous solution.

Studies on neptunium complexation with CMPO- and diglycolamide-functionalized ionic liquids: experimental and computational studies

A CMPO-functionalized task-specific ionic liquid provided significantly greater extraction of Np⁴⁺ than of NpO₂²⁺, which is of interest for radioactive waste treatment.

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.