Insights in uranium extraction from spent nuclear fuels using dicyclohexano-18-crown-6 – Fate of rhenium as technetium homolog

Molecular Hosts for the Sensing and Separation of 99TcO4. Chemistry 2024;30:e202401551. [PMID: 38779975 DOI: 10.1002/chem.202401551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In recent years, European Union member states have hastened energy policy deliberations to address supply and sustainability concerns, placing a significant emphasis on nuclear energy as a means to achieve decarbonization goals. However, despite its significant role in power generation, nuclear energy faces significant challenges linked to fuel reprocessing and waste disposal, that hinder its broader expansion. In this context, the separation of technetium represents a concerning issue. Indeed, technetium's catalytic activity can impede the extraction of uranium, neptunium, and plutonium, affecting waste reprocessing efficiency. Additionally, the stable form of technetium in aerobic conditions, pertechnetate (TcO4 -), poses risks of groundwater contamination due to its mobility and solubility. Hence, sensing and separation of TcO4 - is imperative for both nuclear fuel processing and minimising radioactive contamination in the environment. However, the binding of TcO4 - and its separation from contaminated solutions present challenges due to the acidic (or basic) waste components and the high ionic strength in real matrices. Supramolecular chemists have addressed these issues by designing receptors inspired by molecular recognition principles. This article explores recent advancements and future directions in TcO4 - sensing and separation (using extraction and sorption) with a focus on molecular hosts. Metal-organic receptors will also be discussed.

Rapid and reliable assaying of Tc-99 in sediment samples with novel MTPN polymeric resin

The paper describes a new method for the rapid determination of Technetium (Tc) in sediment samples using solid-phase extraction chromatography (SPEC) with a novel methyl triphenyl phosphoniumnitrate (MTPN) resin. The effectiveness of the resin in selectively recovering Tc was evaluated in both batch and column mode and exploited for rapid analysis of 'Tc'. The procedure involves the acid digestion of samples, pre-concentration of fission products in supernatant and co-precipitation of actinides with Fe(OH)3, followed by selective recovery of Tc by SPEC using a column filled with MTPN resin. The recovered Tc was then radiometrically assayed using beta counting. The method was validated using IAEA certified reference materials and was found to provide reliable and reproducible results for the activity concentration of Tc-99 in sediment samples within 24 h.

Modification of graphene oxide with imidazolium-based ionic liquid for significant sorption of La(III) and Pr(III) from aqueous solutions

A straightforward ferrocyanide immobilization on the surface of graphene oxide (GO) was conducted for rapid and efficient adsorption capacity for lanthanum and praseodymium from an aqueous solution. The GO was mixed with 1-methyl imidazole in the presence of epichlorohydrin to form GO-imidazole-Cl and thereafter suspended in a potassium ferrocyanide solution to fabricate GO-imidazole-FeCN. The prepared materials were characterized with different advanced techniques confirming the preparation method. The adsorption ability of GO-imidazole-FeCN towards La(III) and Pr(III) ions was evaluated. Moreover, the adsorption isotherm showed that the sorption process was fitted with the Langmuir isotherm model with a considerable maximum adsorption capacity of 781.25 mg g−1 for La(III) and 862.07 mg g−1 for Pr(III). The thermodynamic studies showed that the adsorption of both metal ions was spontaneous and endothermic. In addition, the adsorbent showed excellent adsorption–desorption behavior over 5 times, suggesting that GO-imidazole-FeCN may be considered a potential candidate for La(III) and Pr(III) removal from different metal ions which present in fission products.

Ultrafast and selective separation of 99mTc from molybdenum matrix using DBDGA deliberately tailored macrocyclic crown-ethers

Technetium-99m (^99mTc) is an important medical radionuclide. Due to the crisis in supply of molybdenum-99 (⁹⁹Mo), production of ^99mTc directly via the ¹⁰⁰Mo (p, 2 n) reaction by cyclotron was proposed. In this process, the most critical challenge is to rapidly and efficiently separate ^99mTc from high concentration of molybdenum. In this work, a novel ligand, bis(N,N-dibutyldiglycolamide)dibenzo-18-crown-6 (BisDBDGA-DB18C6) was successfully synthesized and used for extraction of TcO₄^- /ReO₄^- from molybdenum. The results demonstrated that BisDBDGA-DB18C6 expressed excellent selectivity for TcO₄^- with a high separation factor of 1.6 × 10⁵ against Mo, a fast extraction kinetic (within 45 s), and a high extraction capacity of 211 mmol ReO₄^- (⁹⁹TcO₄^-)/per mole of extractant. The extraction mechanism was proposed as a co-interaction of macrocyclic crown ether and N,N-dibutyldiglycolamide group through slope analysis, FT-IR, ESI-MS, ¹H NMR titration and theory calculations. Importantly, ⁹⁹Tc in the organic phase can be quantitatively (> 99%) and easily back-extracted using deionized water, which can be directly used for medical applications.

Chelating Extractants for Metals

In the present review, works on the classes of chelating extractants for metals, compounds with several amide and carboxyl groups, azomethines, oximes, macrocyclic compounds (crown ethers and calixarenes), phenanthroline derivatives, and others are systematized. This review focuses on the efficiency and selectivity of the extractants in the recovery of metals from industrial wastewater, soil, spent raw materials, and the separation of metal mixtures. As a result of this study, it was found that over the past seven years, the largest number of works has been devoted to the extraction of heavy metals with amino acids (16 articles), azomethines and oximes (12 articles), lanthanids with amide compounds (15 articles), lanthanides and actinides with phenanthroline derivatives (7 articles), and noble metals with calixarenes (4 articles). Analysis of the literature showed that amino acids are especially effective for extracting heavy metals from the soil; thiodiglycolamides and aminocalixarenes for extracting noble metals from industrial waste; amide compounds, azomethines, oximes, and phenanthroline derivatives for extracting actinides; amide compounds for extracting lanthanides; crown ethers for extracting radioactive strontium, rhenium and technetium. The most studied parameters of extraction processes in the reviewed articles were the distribution ratios and separation factors. Based on the reviewed articles, it follows that chelate polydentate compounds are more efficient compounds for the extraction of metals from secondary resources compared to monodentate compounds.

Synergistic adsorption behavior of a silica-based adsorbent toward palladium, molybdenum, and zirconium from simulated high-level liquid waste

In this study, the synergistic adsorption behavior of palladium [Pd(II)], molybdenum [Mo(VI)], and zirconium [Zr(IV)] in simulated high-level liquid waste was systematically investigated based on various factors, such as the contact time, concentration of nitric acid, adsorption amount, and temperature using a silica-based adsorbent impregnated with N,N'-dimethyl-N,N'-di-n-hexyl-thiodiglycolamide (Crea) and 2, 2', 2' -nitrilotris[N,N-bis(2-ethylhexyl)acetamide] (TAMIA-EH). The adsorption rates of Pd(II), Mo(VI), and Zr(IV) in this synergistic adsorption system were high; thus, equilibrium states could be obtained in only 1 h with high uptake percentages of more than 90%. The adsorption abilities of Pd(II), Mo(VI), and Zr(IV) were only slightly affected by variation in the concentration of nitric acid in the range of 0.1-5 M and solution temperature in the range of 288-313 K. Selective stripping of the adsorbed Re(VII), Pd(II), Zr(IV), and Mo(VI) was successfully achieved under elution with 5 M HNO₃, 0.2 M Tu (pH 1), 50 mM DTPA (pH 2), and 50 mM DTPA dissolved in 0.5 M Na₂CO₃ (pH 11) solutions using the chromatography method. In addition, the adsorption performance in solid-state was studied using the particle-induced X-ray emission (PIXE) method; the obtained results were in good agreement with the results obtained via column separation.

Radiation synthesis of ionic liquid-functionalized silica-based adsorbents: a preliminary investigation on its application for removal of ReO4- as an analog for TcO4. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2021;28:17752-17762. [PMID: 33400123 DOI: 10.1007/s11356-020-12078-z]

The decontamination of radioactive TcO₄^- from nuclear wastes is becoming increasingly crucial for spent nuclear fuel reprocessing and environmental remediation. In this work, a series of ionic liquid-immobilized silica-based adsorbents (SVIL-Cn, n = 1, 4, 8) were newly synthesized using the radiation-induced grafting of 4-vinylbenzyl chloride onto silanized silica and subsequent functionalization with 1-methylimidazole, 1-butylimidazole, or 1-octylimidazole. The synthesis conditions such as the solvent, absorbed dose, and monomer concentration were investigated in detail, and the resulting adsorbents were characterized by elemental analysis, FT-IR, SEM, and TGA. In batch experiments, the adsorbents exhibited a high ReO₄^- (a nonradioactive surrogate of TcO₄^-) removal efficiency over a wide pH range (3 ~ 8), and SVIL-C1 showed a maximum adsorption capacity of 70.62 mg g^-1 towards ReO₄^-. In addition, their adsorption performance barely changed after 800 kGy radiation. The column experiments for treating simulated radioactive wastewater showed that the SVIL-Cn adsorbents could selectively separate TcO₄^-/ReO₄^- from a variety of fission products, and they could be recycled four times with negligible capacity loss. Lastly, XPS and FT-IR analysis confirmed that the adsorption proceeded via an ion-exchange mechanism. The results showed that these adsorbents are suitable for the efficient removal of TcO₄^-/ReO₄^- from radioactive wastewater with complex compositions.

Efficient and Ultrafast Adsorption of Rhenium by Functionalized Hierarchically Mesoporous Silica: A Combined Strategy of Topological Construction and Chemical Modification

Radioactive Tc-99 released by nuclear accidents threatens the environment and human health due to its long half-life and strong transportability. A combined strategy synergizing topological construction and chemical modification was proposed for the synthesis of high-performance adsorbents for Re as an analogue to Tc. On the one hand, hierarchically mesoporous SiO₂ with a fibrous structure (F-SiO₂), a peculiar topology integrating wrinkled open mesopores around 12 nm and on-wall mesopores around 3 nm, was adopted as the substrate of adsorbents. The larger mesopores can act as the superhighway for mass transfer, while the abundant smaller mesopores provide numerous adsorption sites. On the other hand, a series of dicationic pyridine (DCP) derivative groups (-Py⁺C_nH_2nN⁺Me₃) were designed to functionalize F-SiO₂ for improving the adsorption performance toward ReO₄^- anions, the dominating form of Re in aqueous solution. Density functional theory (DFT) calculation combined with batch adsorption experiments revealed that the ReO₄^- adsorption on -Py⁺C₅H₁₀N⁺Me₃ was the most favorable when the length of the spacer between the two positively charged N atoms ranged from 2 to 7 carbons (n = 2-7). However, -Py⁺C₅H₁₀N⁺Me₃ exhibited a much slower adsorption rate than -Py⁺C₂H₄N⁺Me₃. The stronger interaction between ReO₄^- and -Py⁺C₅H₁₀N⁺Me₃ suppresses the adsorbate diffusion. The two positive charges of -Py⁺C₅H₁₀N⁺Me₃ may be perpendicularly distributed, sterically hindering ReO₄^- transport in smaller mesopores. The longer and flexible carbon chains may be aggregated to form the hydrophobic region, repulsing the hydrated ReO₄^- anions. Therefore, the efficient and ultrafast Re adsorption was achieved by synergizing the unique topology of F-SiO₂ and functionalization by -Py⁺C₂H₄N⁺Me₃ with a shorter spacer and weaker affinity ReO₄^-. The detailed investigation demonstrated that -Py⁺C₂H₄N⁺Me₃ possessed exothermic adsorption nature, adequate radiation-resistance, and excellent reusability. Meanwhile, -Py⁺C₅H₁₀N⁺Me₃ exhibited stronger salinity tolerance and higher selectivity. The DCP groups are promising in decontamination of radioactive Tc, as they can meet specific requirements by manipulating the length of spacers.

Radiation synthesis of imidazolium-based ionic liquid modified silica adsorbents for ReO4− adsorption

A series of ionic liquid functionalized silica-based adsorbents were synthesized and used to remove ReO₄⁻ from simulated radioactive wastewater.

Detailed characterization of dioxouranium(vi) complexes with a symmetrical tetradentate N2O2-benzil bis(isonicotinoyl hydrazone) ligand

The reactions of UO2(OAc)2·2H2O with benzil bis(isonicotinoyl hydrazone) ligand (H2L) in varied solvent media resulted in the formation of a series of new dioxouranium(vi) complexes 1-3 of the type UO2(L)(X), [where 1, X = DMF; 2, X = DMSO; 3, X = H2O]. The complexes were systematically characterized by elemental analysis, UV-Visible spectroscopy, TGA, mass spectrometry, cyclic voltammetry, and powder X-ray diffraction study. Among all the complexes, 1 was confirmed by single-crystal X-ray diffraction study. It was found that 1 preferred a distorted pentagonal bipyramidal geometry, in which an equatorial coordination plane was formed by the ONNO-tetradentate cavity of the deprotonated hydrazone ligand along with an additional oxygen atom of the coordinated solvent molecule. Thermal analysis suggested that complexes 1 and 3 undergo weight loss in the temperature range 180-210 °C and 100-120 °C, respectively, due to the ready release of their coordinated solvent molecules. Complexes 1-3 exhibited analogous UV-Visible absorption bands and the intense band between 300-600 nm was assigned to the M ← L and n → π* transitions. Weakly resolved reduction waves assigned to {UO2}2+/{UO2}+ couple were observed for complexes 1 and 2 {1, -1.76 V; 2, -1.75 V; vs. ferrocenium/ferrocene (Fc+/Fc)} in DMSO solution, signifying the feeble electron-donating nature of the L2- ligand. Powder X-ray diffraction study suggested that the crystallite size of all the complexes was in the nanoscale range. Further analysis using density functional theory (DFT) calculations provided structural insights as well as information on the electronic properties of both complex 1 and the ligand.