Extraction Behavior of Metal Ions by TODGA, DOODA, MIDOA, and NTAamide Extractants from HNO3ton-Dodecane

Understanding the Interaction of Uranyl Cation with Two C-Pivot Tripodal Amides: Synthesis, Complexation, Microcalorimetry, and DFT Studies

Complexation of uranyl ions with two structurally related C-pivotal tripodal amides with varying spacer lengths, synthesized for the first time, was studied by optical spectroscopy. In the tripodal amides, the coordination was through the carbonyl O atoms where the carbonyl groups were away from the central C-atom by three spacer atoms (LI) and four spacer atoms (LII), respectively. Increasing the spacer atoms going from LI to LII favors the complexation with the linear uranyl cations and results in stronger complex formation. The complexation heat between the uranyl cations and the two amide ligands was directly measured by microcalorimetric titrations. The complexation with both the ligands was driven by exothermic enthalpy and positive entropy changes. Formation of the complex proceeded by the replacement of water molecules from the primary coordination sphere of the uranyl cation. Both ligands formed bisolvated (ML2-type) complexes in which one unit of the ligand binds in a monodentate manner and the other in a bidentate mode. Density functional theory calculations further supported our experimental observations.

Redox stabilization of Am(v) in a biphasic extraction system boosts americium/lanthanides separation efficiency

Americium (Am) is a key radioactive element in consideration in nuclear waste treatment. Separation of Am from the fission products, lanthanides, is a prerequisite to minimize the hazardous impact of Am and make utilization of rare Am isotopes, but it represents a great challenge due to the chemical similarity between the two groups of elements. Herein, we realize the separation by first oxidizing Am(iii) to high valent Am(vi) and then converting it to Am(v) in situ in a biphasic extraction system with Bi(v) oxidant incorporated in an organic phase. Am(v) is highly stabilized during the separation process and this leads to record high Ln/Am separation factors (>105) in a single contact over a wide range of acidities.

Extraction of Rh(III) from hydrochloric acid by protonated NTAamide(C6) and analogous compounds and understanding of extraction equilibria by using UV spectroscopy and DFT calculations

Extraction of Rh from hydrochloric acid is conducted using NTAamide(C6) (N,N,N´,N´,N´´,N´´-hexahexyl-nitrilotriacetamide) and other related compounds. We use the ion-pair extraction of anionic species of Rh-chloride and protonated extractant. Rh ions exist as Rh(Cl)n(H2O)6-n (n ≤ 5) and the tertiary nitrogen atom in an extractant are protonated to produce a quaternary amine in acidic condition. The D(Rh) values are changeable because the Rh-Cl-H2O complex forms from + 3 to - 2 valency. Rh-chloride ion with a peak of spectrum at 504 nm can be extracted effectively, where RhCl4(H2O)- and RhCl5(H2O)2- exist from Density functional theory calculation and UV spectrum. The maximum distribution ratio (D) of Rh(III) is 16, and 85 mM Rh can be extracted from 1 M HCl dissolving 96 mM, due to less third phase formation. Approximate 80% of Rh can be stripped by the water-soluble reagents having the activities of neutralization and solvation. The figure for the Graphical Index saved in the JPEG, PNG or TIFF format at 300 dpi should be pasted with the size adjusted to the frame below (5 cm long and 8 cm wide).

Tuning the Alkyl Chain of Nitrilotriacetamide for Selectively Extracting Trivalent Am over Eu Ions

The successful management and safe disposal of high-level nuclear waste necessitate the efficient separation of actinides (An) from lanthanides (Ln), which has emerged as a crucial prerequisite. Mixed donor ligands incorporating both soft and hard donor atoms have garnered interest in the field of An/Ln separation and purification. One such example is nitrilotriacetamide (NTAamide) derivatives, which have demonstrated selectivity in extracting minor actinide Am(III) ions over Eu(III) ions. Nevertheless, the Am/Eu complexation behavior and selectivity remain underexplored. In the work, a comprehensive and systematic investigation has been conducted for [M(^RL)(NO₃)₃] complexes (M = Am and Eu) utilizing relativistic density functional theory. The NTAamide ligand (^RL) is substituted with various alkyl groups, namely, methyl, ethyl, propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl. Thermodynamic calculations show that the alkyl chain length in NTAamide is capable of tuning the separation selectivity of Am and Eu. Moreover, the differences in calculated free energies between Am and Eu complexes are more negative for R = Bu-Oct than Me-Pr. This indicates that elongation of the alkyl chain can increase the efficiency of selective separation of Am(III) from Eu(III). Based on the quantum theory of atoms in molecules and charge decomposition analyses, it has been observed that the strength of Am-^RL bonds is higher than that of Eu-^RL bonds. This disparity is attributed to a greater degree of covalency in Am-^RL bonds and a higher level of charge transfer from ligands to Am within complexes containing these bonds. Energies of occupied orbitals with the central N character are recognized overall lower for [Am(^OctL)(NO₃)₃] than for [Eu(^OctL)(NO₃)₃], indicative of stronger complexation stability of the former. These results offer valuable insights into the separation mechanism of NTAamide ligands, which can help guide the development of more powerful agents for An/Ln separation in future applications.

Efficient separation of americium by a mixed solvent of two extractants, a diamideamine and a nitrilotriacetamide

The Japan Atomic Energy Agency (JAEA) has proposed the Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation (SELECT) process by solvent extraction as a new separation technology to recover minor actinides (MA) from high-level liquid waste (HLLW) produced by spent fuel reprocessing. The MA separation in the SELECT process comprises the recovery of MA and rare earths (RE) from HLLW, MA/RE separation, and Am/Cm separation. Three highly practical extractants are used in the MA separation. Furthermore, this flow configuration facilitates the preparation of nitric acid concentrations in the aqueous phase. However, the separation factor between Cm and Nd in the MA/RE separation is small (SF_Cm/Nd = 2.5), requiring many extraction stages for continuous extraction in a mixer settler. Therefore, this study investigated the separation of only Am from an aqueous nitric acid solution containing MA (Am and Cm) and RE using an organic phase mixed with two extractants alkyl diamideamine with 2-ethylhexyl alkyl chains (ADAAM(EH)) and hexa-n-octylnitrilotriacetamide (HONTA) used in the SELECT process. Under high-concentration nitric acid conditions, Am and La, Ce, Pr, Nd (light lanthanides) were extracted in the ADAAM(EH) + HONTA mixed solvent, whereas Cm, medium, and heavy lanthanides, and Y were partitioned in the aqueous phase. Subsequently, only light lanthanides could be back extracted from the ADAAM(EH) + HONTA mixture solvent containing Am and light lanthanides in low nitric acid concentrations. Furthermore, Am could be easily stripped with 0.2 M or 5 M nitric acid. This method does not require the mutual separation of Cm and Nd, which have low separation factors. Am can be efficiently separated by one extraction and two back extractions, reducing the number of steps in the SELECT process.

Complexation of a Nitrilotriacetate-Derived Triamide Ligand with Trivalent Lanthanides: A Thermodynamic and Crystallographic Study

Non-heterocyclic N-donor nitrilotriacetate-derived triamide ligands are one of the most promising extractants for the selective extraction separation of trivalent actinides over lanthanides, but the thermodynamics and mechanism of the complexation of this kind of ligand with actinides and lanthanides are still not clear. In this work, the complexation behaviors of N,N,N',N',N″,N″-hexaethylnitrilotriacetamide (NTAamide(Et)) with four representative trivalent lanthanides (La³⁺, Nd³⁺, Eu³⁺, and Lu³⁺) were systematically investigated by using ¹H nuclear magnetic resonance (¹H NMR), ultraviolet-visible (UV-vis) and fluorescence spectrophotometry, microcalorimetry, and single-crystal X-ray diffractometry. ¹H NMR spectroscopic titration of La³⁺ and Lu³⁺ indicates that two species of 1:2 and 1:1 metal-ligand complexes were formed in NO₃^- and ClO₄^- media. The stability constants of NTAamide(Et) with Nd³⁺ and Eu³⁺ obtained by UV-vis and fluorescence titration show that the complexing strength of NTAamide(Et) with Nd³⁺ is lower than that with Eu³⁺ in the same anionic medium, while that of the same lanthanide complex is higher in ClO₄^- medium than in NO₃^- medium. Meanwhile, the formation reactions for all metal-ligand complexes are driven by both enthalpy and entropy. The structures of lanthanide complexes in the single ClO₄^- and NO₃^- medium and the mixed one were determined to be [LnL₂(MeOH)](ClO₄)₃ (Ln = La, Nd, Eu, and Lu), [LaL₂(EtOH)₂][La(NO₃)₆], and [LaL₂(NO₃)](ClO₄)₂, separately. The average bond lengths of lanthanide complexes decrease gradually with the decrease in ionic radii of Ln³⁺, indicating that heavier lanthanides form stronger complexes due to the lanthanide contraction effect, which coincides with the trend of the complexing strength obtained by spectroscopic titration. This work not only reveals the thermodynamics and mechanism of the complexation between NTAamide ligands and lanthanides but also obtains the periodic tendency of complexation between them, which may facilitate the separation of trivalent lanthanides from actinides.

Size Selective Ligand Tug of War Strategy to Separate Rare Earth Elements

Separating rare earth elements is a daunting task due to their similar properties. We report a "tug of war" strategy that employs a lipophilic and hydrophilic ligand with contrasting selectivity, resulting in a magnified separation of target rare earth elements. Specifically, a novel water-soluble bis-lactam-1,10-phenanthroline with an affinity for light lanthanides is coupled with oil-soluble diglycolamide that selectively binds heavy lanthanides. This two-ligand strategy yields a quantitative separation of the lightest (e.g., La-Nd) and heaviest (e.g., Ho-Lu) lanthanides, enabling efficient separation of neighboring lanthanides in-between (e.g., Sm-Dy).

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.

Experimental and theoretical studies on the extraction behavior of Cf(iii) by NTAamide(C8) ligand and the separation of Cf(iii)/Cm(iii)

In this work we studied the extraction behaviors of Cf(iii) by NTAamide (N,N,N',N',N'',N''-hexaocactyl-nitrilotriacetamide, C8) in nitric acid medium. Influencing factors such as contact time, concentration of NTAamide(C8), HNO3 and NO3 - as well as temperature were considered. The slope analysis showed that Cf(iii) should be coordinated in the form of neutral molecules, and the extraction complex should be Cf(NO3)3·2L (L = NTAamide(C8)), which can achieve better extraction effect under the low acidity condition. When the concentration of HNO3 was 0.1 mol L-1, the separation factor (SFCf/Cm) was 3.34. The extractant has application prospect to differentiate the trivalent Cf(iii) and Cm(iii) when the concentration of nitric acid is low. On the other hand, density functional theory (DFT) calculations were conducted to explore the coordination mechanism of NTAamide(C8) ligands with Cf/Cm cations. The NTAamide(C8) complexes of Cf(iii)/Cm(iii) have similar geometric structures, and An(iii) is more likely to form a complex with 1 : 2 stoichiometry (metal ion/ligands). In addition, bonding property and thermodynamics analyses showed that NTAamide(C8) ligands had stronger coordination ability with Cf(iii) over Cm(iii). Our work provides meaningful information with regard to the in-group separation of An(iii) in practical systems.

Aggregation Behavior of Nitrilotriacetamide (NTAmide) Ligands in Thorium(IV) Extraction from Acidic Medium: Small-Angle Neutron Scattering, Fourier Transform Infrared, and Theoretical Studies

Two tripodal amides obtained from nitrilotriacetic acid with n-butyl and n-octyl alkyl chains (HBNTA(L_I) and HONTA(L_II), respectively) were studied for the extraction of Th(IV) ions from nitric acid medium. The effect of the diluent medium, i.e., n-dodecane alone and a mixture of n-dodecane and 1-decanol, onto aggregate formation were investigated using small angle neutron scattering (SANS) studies. In addition, the influence of the ligand structure, nitric acid, and Th(IV) loading onto ligand aggregation and third-phase formation tendency was discussed.The L_I/L_II exist as monomers (aggregarte radius for L_I: 6.0 Å; L_II:7.4 Å) in the presence of 1-decanol, whereas L_II forms dimers (aggregarte radius for L_II:9.3 Å; L_I does not dissolve in n-dodecane) in the absence of 1-decanol. The aggregation number increases for both the ligands after HNO₃ and Th(IV) loading. The maximum organic concentration (0.050 ± 0.004 M) of Th(IV) was reached without third-phase formation for 0.1 M L_I/L_II dissolved in 20% isodecanol +80% n-dodecane. The interaction of 1-decanol with L_II and HNO₃/Th(IV) with amidic oxygens of L_I/L_II results in shift of carbonyl stretching frequency, as shown by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) studies. The structural and bonding information of the Th-L_I/L_II complex were derived from the density functional theoretical (DFT) studies. The molecular dynamics (MD) simulations suggested that the aggregation behavior of the ligand in the present system is governed by the population of hydrogen bonds by phase modifier around the ligand molecules. Although the theoretical studies suggested higher Gibbs free energy of complexation for Th⁴⁺ ions with L_I than L_II, the extraction was found to be higher with the latter, possibly due to the higher lipophilicity and solubility of the Th-L_II aggregate in the nonpolar media.

Extraction and Complexation Investigation of Palladium(II) by a Nitrilotriacetate-Derived Triamide Ligand

Effective and selective separation and recovery of the fission product palladium from high-level liquid waste are conducive not only to reducing its hazards to the public health and environment but also to alleviate the pressure on the increasing demand for natural palladium. Herein, the Pd²⁺ extraction in an HNO₃ solution with a nitrilotriacetate-derived triamide ligand NTAamide(n-Oct) and the complexation between them were investigated. Using n-octanol as a diluent, NTAamide(n-Oct) demonstrated an excellent selectivity, strong extractability, and high loading capacity for Pd²⁺ extraction. Combined with the results of single-crystal X-ray diffraction, Fourier transform infrared spectroscopy, electrospray ionization-mass spectroscopy, microcalorimetric titration, and slope analysis, the extracted complexes were determined as [PdL₂](NO₃)₂ and [PdL₂][Pd(NO₃)₄] (where L denotes the NTAamide ligand) in 0.10 and 3.0 mol/L HNO₃ solutions, respectively. The extraction model closely depended on the solvation state of Pd²⁺ in the HNO₃ solution. An ion-pair extraction model was proposed and discussed.

Kinetics and mechanism of Eu(III) transfer in tributyl phosphate microdroplet/HNO3 aqueous solution system revealed by fluorescence microspectroscopy

In this study, we reveal an Eu(III) extraction mechanism at the interface between HNO₃ and tributyl phosphate (TBP) solutions using fluorescence microspectroscopy. The mass transfer rate constant at the interface is obtained from the analysis of fluorescence intensity changes during the forward and backward extractions at various HNO₃ and TBP concentrations to investigate the reaction mechanism. This result indicates that one nitrate ion reacts with Eu(III) at the interface, whereas TBP molecules are not involved in the interfacial reaction, which is different from the results obtained using the NaNO₃ solution in our previous study. We demonstrate that the chemical species of Eu(III) complex with nitrate ion and TBP in the aqueous solution play an important role for the extraction mechanism. The rate constants of the interfacial reactions in the forward and backward extractions are (4.0-5.0) × 10^-7 m M^-1 s^-1 and (3.2-3.3) × 10^-6 m s^-1, respectively. We expect that our revealed mechanism provides useful and fundamental knowledge for actual solvent extraction.

Unique selectivity reversal between Am3+ and Eu3+ ions by incorporation of alkyl branching in diglycolamide derivatives: DFT validation of experimental results

Incorporation of alkyl branching at α position in DGA derivative showed reversal of selectivity between Am3+ and Eu3+ which was explained using luminescence spectroscopic and DFT calculations.

A H-Bonding and Electrostatic Interaction Combined Strategy for TcO4- Separation by a Nitrotriacetate-Derived Amine-Amide Extractant

Effective and selective separation of technetium from acidic nuclear liquid waste is highly desirable for partitioning and transmutation but is of significant challenge. Highly efficient extraction of pertechnetate can be achieved by taking H-bonding and electrostatic interaction combined strategy. Base on this strategy, an amine-amide ligand NTAamide(n-Oct) was employed to extract TcO₄^- in HNO₃ solution. Using n-dodecane as a diluent, NTAamide(n-Oct) demonstrated excellent extractability and good selectivity toward TcO₄^- with a rapid extraction equilibrium that could be reached in less than 1 min. Its maximal loading capacity for TcO₄^- was almost 100 times as much as that of traditional amine extractant Aliquat-336 nitrate. Meanwhile, TcO₄^- could be efficiently stripped from the loaded organic phase by (NH₄)₂CO₃ solution. Slope analysis indicated the formation of a 1:1 complex of NTAamide(n-Oct) with TcO₄^-. The extraction conformed to the anion exchange extraction model, as confirmed by analyses of single-crystal X-ray diffraction, ¹H NMR titration, FTIR, and ESI-MS.

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.

Effect of Oxygen-Donor Charge on Adjacent Nitrogen-Donor Interactions in Eu3+ Complexes of Mixed N,O-Donor Ligands Demonstrated on a 10-Fold [Eu(TPAMEN)]3+ Chelate Complex

To reduce high-level radiotoxic waste generated by nuclear power plants, highly selective separation agents for minor actinides are mandatory. The mixed N,O-donor ligand N,N,N',N'-tetrakis[(6-carboxypyridin-2-yl)methyl]ethylenediamine (H₄TPAEN; 1) has shown good performance as a masking agent in Am³⁺/Eu³⁺ separation studies. Adjustments on the pyridyl backbone to raise the hydrophilicity led to a decrease in selectivity and a decrease in M³⁺-N^am interactions. An enhanced basicity of the pyridyl N-donors was given as a cause. In this work, we examine whether a decrease in O-donor basicity can promote the M³⁺-N^am interactions. Therefore, we replace the deprotonated "charged" carboxylic acid groups of TPAEN^4- by neutral amide groups and introduce N,N,N',N'-tetrakis[(6-N″,N''-diethylcarbamoylpyridin-2-yl)methyl]ethylenediamine (TPAMEN; 2) as a new ligand. TPAMEN was crystallized with Eu(OTf)₃ and Eu(NO₃)₃·6H₂O to form positively charged 1:1 [Eu(TPAMEN)]³⁺ complexes in the solid state. Alterations in the M-O/N bond distances are compared to [Eu(TPAEN)]^- and investigated by DFT calculations to expose the differences in charge/energy density distributions at europium(III) and the donor functionalities of the TPAEN^4- and TPAMEN. On the basis of estimations of the bond orders, atomic charges spin populations, and density of states in the Eu and potential Am and Cm complexes, the specific contributions of the donor-metal interaction are analyzed. The prediction of complex formation energy differences for the [M(TPAEN)]^- and [M(TPAMEN)]³⁺ (M³⁺ = Eu³⁺, Am³⁺) complexes provide an outlook on the potential performance of TPAMEN in Am³⁺/Eu³⁺ separation.

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.

Adsorption Behaviors of Palladium Ion from Nitric Acid Solution by a Silica-based Hybrid Donor Adsorbent

The adsorption behaviors of a silica-based hybrid donor adsorbent (TAMIA-EH+1-dodecanol)/SiO2-P towards Pd(II) were investigated under the effect of the contact time, temperature etc. in simulated high-level liquid waste. The adsorption rates of Pd(II) and Re(VII) were fairly fast and could reach the equilibrium state in only 1 h compared with other co-existing metal ions. The adsorption kinetics of Pd(II) was found to fit well with the pseudo-first order model. Even though with increasing the concentration of HNO3 above 1 M, the adsorption performance of (TAMIA-EH+1-dodecanol)/SiO2-P decreased gradually; it still exhibited a better selectivity towards Pd(II) when [HNO3] > 0.5 M. The adsorption isotherms of Pd(II) and Re(VII) were well-described by the Langmuir isotherm model, while the Freundlich isotherm model was considered to be more suitable for the adsorption of Ru(III), Zr(IV) and Mo(VI). A high temperature of an aqueous solution was not good for the effective recovery of Pd(II). The calculated thermodynamic parameters revealed that the adsorption of Pd(II) was exothermic in nature.

Dosimetry and methodology of gamma irradiation for degradation studies on solvent extraction systems

The recycling of minor actinides from dissolved nuclear fuels by hydrometallurgical separation is one challenging strategy for the management of spent fuel. These future separation processes will likely be based on solvent extraction processes in which an organic solvent system (extractant and diluent) will be contacted with highly radioactive aqueous solutions. To establish a separation between different elements in spent nuclear fuel, many extractants have been studied in the past. A particular example is N,N,N′,N′-tetraoctyl diglycolamide (TODGA), which co-extracts lanthanides and actinides from nitric acid solutions into an organic phase (e.g. TODGA in n-dodecane). The radiolytic stability of these extractants is crucial, since they will absorb high doses of ionizing radiation during their usage. Worldwide, different gamma irradiation facilities are employed to expose extractants to ionizing radiation and gain insight in their radiation stability. The facilities differ in many ways, such as their environment (pool-type or dry), configuration and gamma sources (often 60Co or spent nuclear fuel). In this paper, a dosimetric assessment is made using different dosimeter systems in a pool-type irradiation facility, which has the advantage to be flexible in its arrangement of 60Co sources. It is shown that Red Perspex dosimeters can be used to accurately characterize this high dose rate gamma irradiation field (approx. 13.6 kGy h−1), after comparison with alanine, Fricke and ceric-cerous dosimetry in a lower dose rate gamma irradiation field (approx. 0.5 kGy h−1). A final validation of the whole chain of techniques is obtained by reproduction of the dose constants for TODGA in n-dodecane.

Basic Research on Batchwise Multi-stage Extractions Using TODGA for Dy/Nd Separation

The mutual separation of lanthanides has been studied by multi-stage extraction using an extractant, DGA (diglycolamide) compounds. N,N,N',N'-tetraoctyl-DGA (TODGA) has a high extractability to lanthanides and a relatively high separation factor (SF) between Dy and Nd (SF of over 20) from HNO₃ media. Complete separation with such SF values can be achieved by multi-stage extraction. Less information on multi-stage extraction compared to batch extraction has been presented up to now. We thus conducted a basic study. By confirming the experimental data to be identical to calculations, the sample solution including both metals was employed for batchwise multi-stage extraction. Ninety-seven percent of Dy with under detection limit of Nd could be recovered into the organic phase from Nd with a ten-times higher concentration than Dy using the condition, 0.1 M TODGA/n-dodecane and 0.3 M HNO₃ by the multi extraction of 9 × 9 stages for organic and aqueous phases.

Simultaneous separation of Am and Cm from Nd and Sm by multi-step extraction using the TODGA-DTPA-BA-HNO3 system

The simultaneous separation of Am and Cm from lanthanides is important for atomic energy fields. However, the process is difficult owing to the chemical behavior of trivalent metal ions with similar ionic radii. All lanthanides, Am, and Cm can be extracted by diglycolamide (DGA). In addition, relatively high separation factors between An and Ln were obtained by the extraction system of TODGA, DTPA (diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid) and HNO3. In this work, DTPA-BA (diethylenetriamine-N,N′,N″-triacetic-N,N″-bisamide), which is an improved version of DTPA, was employed for the separation of Ln and An. After performing a basic study on DTPA-BA, a relatively high separation factor (approximately 8) for actinides/lanthanides was obtained. Then, the multi-step extraction was performed. Thus, the recoveries of 94.7 % for Nd and 4.7 % for Am and Cm in organic phase, and 5.3 % Nd and 95.3 % for Am and Cm in aqueous phase were obtained.

Effects of Diluents on the Separation of Minor Actinides from Lanthanides with Tetradodecyl-1,10-phenanthroline-2,9-diamide from Nitric Acid Medium

To investigate the effective separation of actinides (Ans) from lanthanides (Lns), single-stage batch extraction experiments were performed with a novel extractant, tetradodecyl-1,10-phenanthroline-2,9-diamide (TDdPTDA) with various diluents such as 3-nitrobenzotrifluoride (F-3), nitrobenzene, and n-dodecane for Am, Cm, and Lns. The extraction kinetics with TDdPTDA was rapid enough to perform continuous extraction experiments using mixer-settler extractors. The slopes of the distribution ratio versus the TDdPTDA concentration and the distribution ratio versus the nitric acid concentration were similar for F-3 and nitrobenzene systems, but different from the n-dodecane system. These differences were attributed to the characteristics of the diluents. This study revealed high distribution ratios of Am (DAm) and Cm (DCm) for TDdPTDA, with the high separation factors (SFs) of Am from Lns enough for their separation.

Activation of the Aromatic Core of 3,3'-(Pyridine-2,6-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol)-Effects on Extraction Performance, Stability Constants, and Basicity

The "CHON" compatible water-soluble ligand 3,3'-(pyridine-2,6-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PTD) has shown promise for selectively stripping actinide ions from an organic phase containing both actinide and lanthanide ions, by preferential complexation of the former. Aiming at improving its complexation properties, PTD-OMe was synthesized, bearing a methoxy group on the central pyridine ring, thus increasing its basicity and hence complexation strength. Unfortunately, solvent extraction experiments in the range of 0.1-1 mol/L nitric acid proved PTD-OMe to be less efficient than PTD. This behavior is explained by its greater pK_a value (pK_a = 2.54) compared to PTD (pK_a = 2.1). This counteracts its improved complexation properties for Cm(III) (log β₃(PTD-OMe) = 10.8 ± 0.4 versus log β₃(PTD) = 9.9 ± 0.5).