Tetra-2-ethylhexyl Diglycolamide Research Articles

Ligand structure and diluent nature in defining improved Am3+ and Cm3+ separation using diglycolamides: a combined solvent extraction and DFT study.

Separation of Am3+ and Cm3+ is one of the most challenging yet unavoidable steps in the back end of the nuclear cycle. Various ligands evaluated for Am/Cm separation have their own merits and demerits, and not a single ligand has been uniquely proposed for this purpose. In the present work, we evaluated N,N,N',N'-tetra-n-octyldiglycolamide (TODGA) vis-à-vis N,N,N',N'-tetra-2-ethylhexyldiglycolamide (T2EHDGA) in combination with a hydrophilic 2,6-bis(1,2,4-triazinyl)pyridine (SO3PhBTP) derivative in the aqueous phase for the separation of Am3+ and Cm3+ from nitric acid medium. The results showed that marginal selectivity for Am3+ over Cm3+ was observed with T2EHDGA in the presence of SO3PhBTP, which was attributed to the difference in the entropy change for their extraction from both the temperature-dependent liquid-liquid extraction and computational studies.

Charge Inversion of Mono- and Dianions to Cations via Triply Charged Metal Complexes: Application to Lipid Mixtures.

Electrospray ionization (ESI) of mixtures can give rise to ions with different masses and charges with overlapping mass-to-charge (m/z) ratios. Such a scenario can be particularly problematic for the detection of low-abundance species in the presence of more highly abundant mixture components. For example, negative mode ESI of polar lipid extracts can result in highly abundant singly charged glyerophospholipids (GPLs), such as phosphatidylethanolamines (PE) and phosphatidylglycerols (PG), that can obscure much less abundant cardiolipins (CLs), which are complex phospholipids with masses roughly double those of GPLs that mostly form doubly charged anions. Despite their low relative abundance, CLs are lipidome components that perform vital biological functions. To facilitate the study of CLs in lipid mixtures without resorting to offline or online separations, we have developed a gas-phase approach employing ion/ion reactions to charge invert anionic lipid species using a trivalent metal-complex. Specifically, ytterbium(III) is shown to readily complex with three neutral ligands, N,N,N',N'-tetra-2-ethylhexyl diglycolamide (TEHDGA), to form [Yb(TEHDGA3)]3+ using ESI. Herein, we describe pilot studies to evaluate [Yb(TEHDGA)3]3+ as an ion/ion reagent to allow for chemical separation of doubly and singly charged anions, using lipid mixtures as examples, without neutralizing ions of either charge state.

Developing N,N,N’,N’-tetra (2-ethylhexyl) diglycolamide encapsulated polymeric beads as promising rare earth extracting agents

ABSTRACT The multi-faceted applications of rare earth elements (REE) in science and technology are not unknown. Scarcity in the primary sources of RE makes it necessary to explore different secondary sources available. Availability of REE in significant amount in spent NdFeB magnetic scrap makes the recycling of REE from this scrap, a lucrative option. In this work, synthetic solutions of 10 g/L (containing the rare earths Nd, Pr and Dy along with Fe) were equilibrated with the organic extractant N,N,N,’N’-tetra (2-ethylhexyl) diglycolamide (TEHDGA) encapsulated in polyethersulfone beads to study the extraction behavior of the REEs from nitric acid medium. Iron (Fe), the major component present in NdFeB scrap, poses the biggest challenge for rare earth extraction from the scraps. The TEHDGA impregnated polymeric beads were found to selectively extract the REEs, leaving Fe(III) in the feed solution. TEHDGA displayed higher selectivity towards the heavier rare earth Dy followed by Nd and Pr. The loading capacity of the beads was measured to be > 1700 ppm. The effect of different experimental parameters, such as contact time, solid-liquid ratio, TEHDGA concentration, feed acidity, were investigated. Contact time of 24 h, TEHDGA concentration of 0.75 M, solid-liquid ratio either 1:5 or 1:10 and feed acidity between 2 and 5 M have been found to suitable for quantitative extraction of REE particularly Dy(III). The recovery of the REEs from the loaded TEHDGA beads was > 90%. Furthermore, the experiment was carried out with higher quantity of beads and feed solution to study applicability of the same in bulk scale. A novel, easy and single-step separation of REE from Fe has been presented in this work.

Low and High LET Degradation Studies of Metal-Loaded Organic Phase Ligands in the ALSEP Process

ABSTRACT Organic solutions comprising the Actinide Lanthanide Separation Process (ALSEP) solvent consisting of 0.5 M 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and 0.05 M N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) in n-dodecane were subjected to low LET and high LET irradiation before and after equilibration with an aqueous phase of 3 M HNO3. Degradation dose constants revealed greater ligand degradation due to gamma irradiation than alpha irradiation for both ligands. Furthermore, equilibration with nitric acid did not have a significant impact on ligand degradation for either irradiation source. Identified degradation products were similar for both gamma and alpha irradiation and occurred mostly through the rupture of the N–Ccarbonyl and C–Oether bonds for T2EHDGA and the C–Oether bond in HEH[EHP]. Acid contact appears to alter the degradation pathway by favoring the formation of higher molecular weight recombination products. Mixed T2EHDGA-HEH[EHP]-NO3 complexes were formed with Nd(III) after extraction from 3 M HNO3, and low LET gamma irradiation of the Nd(III) loaded organic solution produced similar degradation products as the organic solution absent of Nd(III). Interestingly, and likely due to the greater radiolytic susceptibility of T2EHDGA than HEH[EHP], a HEH[EHP]-Nd(III) complex appears to form as the T2EHDGA degrades with increasing absorbed dose.

Application of Impregnated Resins for the Recovery of Actinides from Alpha Contaminated Solid Waste

AbstractAn extraction chromatographic separation scheme has been developed using impregnated resin for the processing of actual plutonium contaminated solid analytical assorted waste. The effluent obtained on anion exchange chromatography during plutonium purification step was processed by tri‐n‐butyl phosphate (TBP) and tetra 2‐ethylhexyl diglycolamide (T2EHDGA) augmented XAD‐4 resin to remove uranium and americium, respectively, while Ag ion was electrochemically separated further. The augmentation of TBP and T2EHDGA functionalities on XAD‐4 have been evidenced by FTIR spectroscopy, TG and DSC analysis. The modification in surface morphology on augmentation has been investigated by SEM, while elemental mapping and EDS heteroatom analysis indicated the successful functionalization/impregnation of the resin. In case of U removal by TBP augmented XAD‐4 resin, starting from 3 gL−1 feed in 7.2 M HNO3, a maximum of 93 % U was found to be loaded on the column, which can quantitatively be back extracted by 0.01 M HNO3. Despite ∼10 % reduction in loading capacity during the 3rd consecutive cycle, the efficacy of this column chromatographic separation of U has been demonstrated successfully. The raffinate of this step was used as feed for Am3+ separation using T2EHDGA‐XAD‐4. A maximum of 98 % loading and almost quantitative elution have been observed during this step and the performance recyclability has been checked for three consecutive cycles. The loading of U and Eu (Am analogue) has been evidenced by elemental mapping and energy‐dispersive X‐ray spectroscopy (EDS)analyses of loaded resin.

Characterization of the ALSEP Process: Investigating Equilibrium and Intermediate Complexes of the Scrub Stage

ABSTRACT A unique combination of real-time and conventional optical spectroscopy, off-line chemical analyses, and equilibrium solvent extraction measurements were employed to monitor progressive changes in the speciation of the organic-phase complexes of neodymium or americium in the biphasic scrub stage of the Actinide-Lanthanide Separation (ALSEP) solvent extraction process proposed for trivalent actinide/lanthanide separations. Consistent with the findings of other researchers, four unique organic-phase species are identified by three separate methods of multivariate analysis. The organic phase initially contains M(TEHDGA)2(HEH[EHP])2(NO3)3 complexes. As the ALSEP organic phase is scrubbed with an aqueous malonate buffer, the complex loses HNO3 to form M(TEHDGA)2(H(EH[EHP])2)(NO3)2 as the first organic-phase intermediate species. Further contact with the scrub aqueous phase forms a second intermediate species, M(TEHDGA)(H(EH[EHP])2)2(NO3), and eventually a complex containing only HEH[EHP], M{H(EH[EHP])2}3 (where TEHDGA = N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide and HEH[EHP] = 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester). Similar intermediate species were also observed in equilibrium ALSEP organic phases when lower aqueous concentrations of nitric acid (e.g., 0.5 M HNO3) were used to extract actinides or lanthanides.

Behaviors of ALSEP Organic Extractants: an Atomic Perspective Derived from Molecular Dynamics Simulation

ABSTRACT Molecular dynamics simulations were performed on mixtures of N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) and 2-ethylhexylphosphonic acid mono(2-ethylhexyl) ester (HEHEHP) extractants in a dodecane-water system in order to understand the organization and interfacial behavior of extractants in the Actinide-Lanthanide Separation (ALSEP) process. The dynamic behavior and coordination environments of these extractants near the interface were investigated as a function of aqueous nitric acid concentration in the range 0–6 M HNO3. To gain a complete molecular picture of the extractants’ interfacial behaviors, the effects of varying acidity were scrutinized in the context of spatial distributions of extractants within a given phase, chemical interactions, interfacial orientation, and extractant conformation. While the composition of the interfacial solvent mixing region changed with increasing acidity, the behavior of both extractants exhibited very little response to the varying acid levels, but in their own distinct manner. HEHEHP was found to express a specific interfacial behavior marked by a stronger affinity for the interface, with the polar POOH head group being oriented toward the interface and the alkyl chains residing in a constrained conformation. The larger and more flexible extractant, T2EHDGA, is less strongly associated with the interfacial region, on average dwells deeper into the organic phase, and displays orientations and conformations that are more like those of bulk organic phase T2EHDGA molecules than the ordered HEHEHP molecules.

First Report on the Complexation of Uranyl Ion with Two Diglycolamide Ligands in a Room Temperature Ionic Liquid: Optical Spectroscopy and Calorimetric Studies

AbstractThe complexation of UO22+ with N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) and N,N,N′,N′‐tetra‐2‐ethylhexyl diglycolamide (T2EHDGA) was investigated in ionic liquid using UV−vis absorption spectrophotometry and isothermal titration calorimetry. Spectrophotometric titration suggested the formation of two successive complexes, [UO2L]2+ and [UO2L2]2+ where L=TODGA or T2EHDGA. The formation constant values obtained in ionic liquid medium were several orders of magnitude higher than those observed with the analogous DGA ligands in aqueous medium. The stability constant (logβ) for UO22+/TODGA complex was at least an order of magnitude higher than those observed for UO22+/T2EHDGA complex. The speciation of UO22+/DGA complex obtained by spectrophotometric titration was in conformity with those observed in biphasic solvent extraction. Energetically the UO22+/DGA complexation was mainly driven by negative enthalpy and large positive entropy changes as a result of the release of entire water molecules from the solvation sphere of the hydrated UO22+ ions. The results from this work gave an insight understanding of the complexation behaviour of UO22+ ions with DGA ligands in ionic liquid. It is anticipated that such understanding will give valuable information for understanding the extraction behavior of uranyl ions by DGA ligands in ionic liquid.

Thermal stability assessment of a completely incinerable ionic liquid system in presence of nitric acid – A calorimetric study

The thermal stability of a novel CHON (Carbon, Hydrogen, Oxygen and Nitrogen) based ionic liquid: Methyltrioctylammonium nitrate ([N1888] [NO3]), used for the separation of actinides and fission products was studied using an adiabatic calorimeter (in air ambience under heat-wait-search (HWS) mode) for the first time. The decomposition study of [N1888] [NO3] was accomplished in the presence and absence of nitric acid and a diglycolamide based extractant: N,N,N',N'-tetra(2-ethylhexyl) di-glycolamide (T2EHDGA) which is also incinerable in nature. The neat ionic liquid system showed stability up to 491 K followed by the self decomposition irrespective of the presence or absence of 0.1 M T2EHDGA. The thermal decomposition data on the nitric acid equilibrated ionic liquid phases were generated and were compared with that of ionic liquid – nitric acid biphase. A remarkable difference in the exothermic excursions and derived thermo-kinetic parameters corroborated the impact of nitric acid on the thermal stability of [N1888][NO3].

Selective permeation of 90Y from a mixture of 90Y/90Sr through diglycolamide impregnated supported liquid membranes

An attempt was made in this work to evaluate a simple flat sheet supported liquid membrane technique for the separation of carrier free 90Y from 90Sr using two diglycolamide carrier ligands, (i) N,N,N′,N′-tetra-n-octyl-diglycolamide (TODGA), and (ii) N,N,N′,N′-tetra-(2-ethylhexyl)-diglycolamide (TEHDGA). Various experimental parameters were optimized to get selective transport of 90Y over 90Sr. At 6 M HNO3 feed acidity, >95% 90Y could be recovered selectively in just 4 h with both the ligands. Under identical experimental conditions, about 0.1% transport of Sr was also recorded which could be completely removed by passing through a Sr selective column to get medical grade 90Y pure product. A mathematical model equation was also derived and experimentally validated for predicting the transport of 90Y through membrane.

Structure Activity Relationship Approach toward the Improved Separation of Rare-Earth Elements Using Diglycolamides.

The separation of adjacent lanthanides continues to be a challenge worldwide because of the similar physical and chemical properties of these elements and a necessity to advance the use of clean-energy applications. Herein, a systematic structure-performance relationship approach toward understanding the effect of N-alkyl group characteristics in diglycolamides (DGAs) on the separation of lanthanides(III) from a hydrochloric acid medium is presented. In addition to the three most extensively studied DGA complexants [N,N,N',N'-tetra(n-octyl)diglycolamide, TODGA; N,N,N',N'-tetra(2-ethylhexyl)diglycolamide, TEHDGA; N,N'-dimethyl-N,N'-di(n-octyl)diglycolamide, DMDODGA], 12 new extracting agents with varying substitution patterns were designed to study the interplay of steric and electronic effects that control rare-earth element extraction. Subtle changes in the structure around diglycolamide carbonyl oxygen atoms result in dramatic shifts in the lanthanide extraction strength and selectivity. The effects of the chain length and branching position of N-alkyl substituents in DGAs are elaborated on with the use of experimental, computational, and solution-structure characterization techniques.

Countercurrent Actinide Lanthanide Separation Process (ALSEP) Demonstration Test with a Simulated PUREX Raffinate in Centrifugal Contactors on the Laboratory Scale

An Actinide Lanthanide Separation Process (ALSEP) for the separation of trivalent actinides (An(III)) from simulated raffinate solution was successfully demonstrated using a 32-stage 1 cm annular centrifugal contactor setup. The ALSEP solvent was composed of a mixture of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N′,N′-tetra-(2-ethylhexyl)-diglycolamide (T2EHDGA) in n-dodecane. Flowsheet calculations and evaluation of the results were done using the Argonne’s Model for Universal Solvent Extraction (AMUSE) code using single-stage distribution data. The co-extraction of Zr(IV) and Pd(II) was prevented using CDTA (trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid) as a masking agent in the feed. For the scrubbing of co-extracted Mo; citrate-buffered acetohydroxamic acid was used. The separation of An(III) from the trivalent lanthanides (Ln(III)) was achieved using citrate-buffered diethylene-triamine-N,N,N′,N″,N″-pentaacetic acid (DTPA), and Ln(III) were efficiently back extracted using N,N,N′,N′-tetraethyl-diglycolamide (TEDGA). A clean An(III) product was obtained with a recovery of 95% americium and curium. The Ln(III) were efficiently stripped; but the Ln(III) product contained 5% of the co-stripped An(III). The carryover of Am and Cm into the Ln(III) product is attributed to too few actinide stripping stages, which was constrained by the number of centrifugal contactors available. Improved separation would be achieved by increasing the number of An strip stages. The heavier lanthanides (Pr, Nd, Sm, Eu, and Gd) and yttrium were mainly routed to the Ln product, whereas the lighter lanthanides (La and Ce) were mostly routed to the raffinate.

Investigations on the unusual aggregation behaviour of tetra(2-ethyhexyl)diglycolamide in n-dodecane medium upon gamma irradiation

The limit of reverse micellar aggregation of amphiphilic ligands in n-dodecane medium, known as the third phase formation, is an undesirable event during the course of solvent extraction. The tetraalkyl diglycolamide (DGA) in n-dodecane (n-DD) is a promising solvent medium for the extraction of trivalent actinides from high-level nuclear waste, but it is susceptible to third phase formation. The DGAs in n-dodecane medium undergo a number of chemical transformations in organic phase, known as the radiolytic degradation products, when it was contacted with nuclear waste. While the effect of radiolytic degradation products on the solvent extraction behaviour of actinides was reasonably understood, the third phase formation and reverse micellar aggregation behaviour of the radiolytically degraded DGAs/n-DD has been not explored so far and unfamiliar to the solvent extraction community. To unravel the effect of radiolytic degradation on the aggregation behaviour(third phase formation) of DGAs in n-DD, the following categories of liquids comprising of (1) 0.2 M solution of tetra(2-ethylhexyl)diglycolamide (TEHDGA) present in n-DD, (2) TEHDGA alone, (3) n-dodecane alone, and (4) 0.2 M TEHDGA/n-DD in the presence of extracted nitric acid, were irradiated to a specified absorbed dose levels (10 kGy to 500 kGy) in a 60Co gamma irradiator. The irradiated liquids were made to a solution of 0.2 M TEHDGA in n-dodecane, if required, and the extraction behaviour of nitric acid in the irradiated organic phase was studied. The organic phase obtained after extraction was subjected to dynamic light scattering studies to explore the aggregation behaviour of TEHDGA in organic phase and compared with those obtained before extraction and irradiation. The results revealed that the formation of polar degradation products upon irradiation minimized the aggregation, and the production of higher homologs of n-paraffins enhanced aggregation. In reality, the formation of nitration and other polar radiolytic degradation products in organic phase, confirmed by FTIR spectroscopy, minimized the aggregation and therefore prevented the third phase formation to a significant extent in the present system.

Investigations on the physicochemical properties of a combined extractant system under unirradiated and irradiated conditions

The physicochemical properties of the combination of a neutral and an acidic extractant used in the one cycle process for the mutual separation of An(III) and Ln(III) have been investigated in detail. The extractants used are: N,N,N′,N′-tetra(2-ethylhexyl) diglycolamide (T2EHDGA) and bis(2-ethylhexyl)phosphoric acid (D2EHPA) dissolved in n-dodecane (n-DD). The properties such as dynamic viscosity (η), density (ρ), phase separation time (PST) and interfacial tension (IFT) were measured as a function of various experimental parameters such as temperature, concentration of extractant, the concentration of nitric acid, etc., for both irradiated and unirradiated solvent phases. The change in viscosity and density of 0.1 M T2EHDGA/n-DD phase was ascertained by varying the concentration of D2EHPA from 0.1 M to 0.3 M in it owing to find out the effect of D2EHPA in the organic phase and it showed the increasing trend in both viscosity and density values upon addition of D2EHPA. The energy of activation and the isobaric coefficient of thermal expansion of the solvent phases were accessed. The refractive index (n) of T2EHDGA, D2EHPA and their mixture in n-DD phase was also evaluated in neat as well as irradiated conditions and reported in the paper.

Characterization of the ALSEP Process at Equilibrium: Speciation and Stoichiometry of the Extracted Complex.

We have determined the identity of the complexes extracted into the ALSEP process solvent from solutions of nitric acid. The ALSEP process is a new solvent extraction separation designed to separate americium and curium from trivalent lanthanides in irradiated nuclear fuel. ALSEP employs a mixture of two extractants, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (TEHDGA) in n-dodecane, which makes it difficult to ascertain the nature of the extracted metal complexes. It is often asserted that the weak acid extractant HEH[EHP] does not participate in the extracted complex under ALSEP extraction conditions (2–4 M HNO3). However, the analysis of the Am extraction equilibria, Nd absorption spectra, and Eu fluorescence emission spectra of metal-loaded organic phases argues for the participation of HEH[EHP] in the extracted complex despite the high acidity of the aqueous phases. The extracted complex was determined to contain fully protonated molecules of HEH[EHP] with an overall stoichiometry of M(TEHDGA)2(HEH[EHP])2·3NO3. Computations also demonstrate that replacing one TEHDGA molecule with one (HEH[EHP])2 dimer is likely energetically favorable compared to Eu(TEHDGA)3·3NO3, whether the HEH[EHP] dimer is monodentate or bidentate.

Selective removal of Am(III) and Pu(IV) from analytical waste solutions of quality control operations using extractant encapsulated polymeric beads

Present study reports simultaneous batch and column extraction of Pu(IV) and Am(III) followed by selective stripping from actual analytical waste solution generated during quality control operations. N, N, N′, N′ tetra(2-ethylhexyl) diglycolamide (TEHDGA), di(2-ethylhexyl) phosphoric acid (DEHPA), individually and their combination, encapsulated in polyether sulphone resin beads have been investigated. TEHDGA + DEHPA encapsulated resin showed better performance with respect to kinetics (2 h) and extent of extraction (KD ~ 8000 at 5 M nitric acid) for both Am(III) and Pu(IV). Interesting presence of DEHPA, inefficient as extractant at high nitric acid molarity, improved polymer extraction characteristics. Extraction selectivity over assorted metal ions and reusability for three cycles of operations was established.

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

ABSTRACTDiglycolamides have been proposed for partitioning of trivalent actinides from high-level liquid waste (HLLW). Third-phase formation is an undesirable event during the course of solvent extraction of trivalent actinides from HLLW into the solution of N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (TEHDGA) in n-dodecane (n-DD). Polar reagents such as tri-n-butyl phosphate (TBP), and N,N-dihexyloctanamide (DHOA) have been added to the TEHDGA phase, as phase modifiers in significant concentration, to overcome the third-phase formation. To understand the role of these phase modifiers in controlling the third-phase formation, the extraction behaviour of nitric acid and the trivalent representative metal ion Nd(III) was studied in a binary solution containing TEHDGA and phase modifier in n-dodecane. The organic phase obtained after extraction was subjected to dynamic light-scattering studies to examine the aggregation behaviour of the reverse micelles formed upon extraction and to unravel the unique role of TBP and DHOA in controlling the third-phase formation. The study revealed that the addition of these modifiers brought down the average size of aggregates and their distribution in organic phase below the limiting aggregate size for third-phase formation and increased the dispersion of aggregates in the n-dodecane phase. Among the two phase modifiers proposed for trivalent actinide separation from HLLW, TBP has been identified as a promising reagent for minimizing the third-phase formation.

Investigations on the radiation stability of incinerable CHON based ionic liquid containing diglycolamide

The radiolytic degradation of tetra-2-ethylhexyl diglycolamide (T2EHDGA) and its solution with methyltrioctylammonium nitrate ([N1888][NO3]) was assessed by irradiating the individual liquids and the solution of T2EHDGA in [N1888][NO3] to different γ-absorbed dose levels, and determining the distribution ratio of Am(III) and Nd(III) in the irradiated organic phases. The data obtaining for the irradiated liquids were compared with those obtained for unirradiated liquid phase as well as with the conventional organic phase composed of T2EHDGA in n-dodecane (n-DD). While the distribution ratio of Am(III) in irradiated T2EHDGA/n-DD decreased with increase of absorbed dose, it was invariant in case of irradiated T2EHDGA/[N1888][NO3]. To understand this discrepancy, the distribution ratio of Am(III) as well as the loading behavior of Nd(III) in a solution of irradiated T2EHDGA present in unirradiated [N1888][NO3] as well as in the unirradiated T2EHDGA present in irradiated [N1888][NO3] was measured and compared. The results revealed that the irradiated systems containing either the irradiated T2EHDGA or irradiated [N1888][NO3] undergo degradation upon γ-irradiation, but when they were combined, they mutually facilitate the extraction of Am(III) and Nd(III) comparable to that observed in the unirradiated condition. This observation was also supported by the FTIR spectroscopic investigation of the irradiated organic phases.

Effect of pKa of organophosphorus acidic extractants on the aggregation behavior of diglycolamide in n-dodecane

To understand the role of pKa of the organophsophorus acidic extractant on the reverse micellar aggregation behavior of the binary solution containing tetra-(2-ethylhexyl)diglycolamide (TEHDGA) + acidic extractant in n-dodecane, the extraction behavior of nitric acid and Nd(III) in the binary solution was studied. The acidic extractants chosen were bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX-272), bis(2-ethylhexyl)phosphonic acid (PC88A) and bis(2-ethylhexyl)phosphoric acid (HDEHP). The results revealed that the acidic extractant with lower pKa produced aggregates of smaller size, and therefore, the binary solution containing TEHDGA and HDEHP in n-DD was identified as the promising solvent for the extraction of trivalent metal ions from nuclear waste.

Thermodynamics of Mixing of TEHDGA with Isodecanol in Dodecane: Effect of Equilibration with Aqueous Nitric Acid

The use of any new extractant requires the study of its tendency to form third phases. To understand the phase separation process it is important to have knowledge of the molecular scale phenomena present in the system. This includes the mixing of the substances and the behavior and nature of the aggregates. Here we report the mixing properties of N,N,N′,N′-tetra-(2-ethyl hexyl) diglycolamide (TEHDGA)–dodecane–isodecanol (in the absence and presence of micellar aggregates) which is recognized as a promising system for the separation of minor actinides through the conventional solvent extraction route. The nature of interactions between TEHDGA and isodecanol was investigated using several techniques, including density and speed of sound measurements, ultraviolet absorption spectroscopy and computational studies. The TEHDGA–isodecanol interaction was found to be favored over the inter-isodecanol interaction. On equilibrating the organic phase with nitric acid, some indication of pre-micellar aggregation was obtained. Increase of micellar aggregate size on addition of isodecanol was indicated.