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Polymerized high internal phase emulsions (poly(HIPE)s) are porous polymer monoliths whose synthesis can easily be tailored to allow incorporation of functional units. In this work, nitrile containing poly(HIPE)s have been prepared with either acrylonitrile (AN) or 4-cyanostyrene (4CS) comonomers. Post-synthetic modification of these nitrile-containing poly(HIPE)s yields their corresponding amidoximated analogues, which were studied for actinide uptake. These amidoxime-functionalized, porous polymers were shown to adsorb 95 % Th4+ species from aqueous solution within 30 minutes. In contrast to other amidoxime containing polymers the uptake of UO2 2+ in these poly(HIPE)s is lower under similar conditions. A critical analysis of actinide separations and high-energy X-ray scattering data provides insight into the polymers' selectivity, enabled by the uptake of multinuclear Th clusters.

Uptake characteristics of a bis-amidoximated polymer are presented for 90Sr2+, 137Cs+, and 233UO22+ to assess rational ligand design and polymer engineering efforts applied to selective uranium extraction. Functionalized with the bis-amidoxime diaryl ether ligand at a loading of 1.98 mmol per gram of polymer, the polymer was found to sorb uranium from a pH 6 solution with a separation factor (α) over cesium of 1.2 × 103. Strontium uptake was negligible throughout the pH range studied whereas cesium uptake averaged

The extraction behavior of a quaternary alkylammonium salt extractant was investigated for its selectivity for trivalent actinides over trivalent lanthanides in nitrate and thiocyanate media. The selectivity was evaluated by solvent extraction experiments through radiochemical analysis of 241Am and 152/154Eu. Solvent extraction distribution and slope-analysis experiments were performed with americium(III) and europium(III) with respect to the ligand (nitrate and thiocyanate), extractant, and metal (europium only) concentrations. Further evaluation of the equilibrium expression that governs the extraction process indicated the appropriate use of the saturation method for estimation of the aggregation state of quaternary ammonium extractants in the organic phase. From the saturation method, we observed an average aggregation number of 5.4 ± 0.8 and 8.5 ± 0.9 monomers/aggregate for nitrate and thiocyanate, respectively. Through a side-by-side comparison of the nitrate and thiocyanate forms, we discus...

Organic phase aggregation behavior of 1-octanol and its structural isomer, 2-ethylhexanol, in a biphasic n-dodecane-water system is studied with a combination of physical measurement, small-angle X-ray scattering (SAXS), and atomistic molecular dynamic simulations. Physical properties of the organic phases are probed following their mixing and equilibration with immiscible water phases. Studies reveal that the interfacial tension decreases as a function of increasing alcohol concentration over the solubility range of the alcohol with no evidence for a critical aggregate concentration (cac). An uptake of water into the organic phases is quantified, as a function of alcohol content, by Karl Fischer titrations. The extraction of water into dodecane was further assessed as a function of alcohol concentration via the slope-analysis method sometimes employed in chemical separations. This method provides a qualitative understanding of solute (water/alcohol) aggregation in the organic phase. The physical results are supported by analyses of SAXS data that reveals an emergence of aggregates in n-dodecane at elevated alcohol concentrations. The observed aggregate structure is dependent on the alcohol tail group geometry, consistent with surfactant packing parameter. The formation of these aggregates is discussed at a molecular level, where alcohol-alcohol and alcohol-water H-bonding interactions likely dominate the occurrence and morphology of the aggregates.

The sterically constrained, macrocyclic, aqueous soluble ligand N,N′-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H2BP18C6) was investigated for separating americium from curium and all the lanthanides by solvent extraction. Pairing H2BP18C6, which favors complexation of larger f-element cations, with acidic organophosphorus extractants that favor extraction of smaller f-element cations, such as bis-(2-ethylhexyl)phosphoric acid (HDEHP) or (2-ethylhexyl)phosphonic acid mono(2-ethylhexyl) ester (HEH[EHP]), created solvent extraction systems with good Cm/Am selectivity, excellent trans-lanthanide selectivity (Kex,Lu/Kex,La = 108), but poor selectivity for Am against the lightest lanthanides. However, using an organic phase containing both a neutral extractant, N,N,N’,N’-tetra(2-ethylhexyl)diglycolamide (TEHDGA), and HEH[EHP] enabled rejection of the lightest lanthanides during loading of the organic phase from aqueous nitric acid, eliminating their interference in the americium stripping stages. ...

Complexation of the adjacent actinide ions americium(III) and curium(III) by the ligand N,N'-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6 (H2bp18c6) in aqueous solution was studied to quantify and characterize its americium/curium selectivity. Liquid-liquid extraction and spectrophotometric titration indicated the presence of both fully deprotonated and monoprotonated complexes, An(bp18c6)(+) and An(Hbp18c6)(2+) (An = Am or Cm), at the acidities that would be encountered when treating nuclear wastes. The stability constants of the complexes in 1 M NaNO3 determined using competitive complexation were log β101 = 15.49 ± 0.06 for Am and 14.88 ± 0.03 for Cm, indicating a reversal of the usual order of complex stability, where ligands bind the smaller Cm(III) ion more tightly than Am(III). The Am/Cm selectivity of bp18c6(2-) that is defined by the ratio of the Am and Cm stability constants (β101 Am/β101 Cm = 4.1) is the largest reported so far for binary An(III)-ligand complexes. Theoretical density functional theory calculations using the B3LYP functional suggest that the ligand's size-selectivity for larger 4f- and 5f-element cations arises from steric constraints in the crown ether ring. Enhanced 5f character in molecular orbitals involving actinide-nitrogen interactions is predicted to favor actinide(III) complexation by bp18c6(2-) over the complexation of similarly sized lanthanide(III) cations.

The solvent extraction of 12-phosphotungstic acid, also known as 12-tungstophosphoric acid—H3PW12O40, the so-called Keggin heteropolyacid—by 0.73 M (20%v/v) tri-n-butyl phosphate (TBP) in n-octane under conditions comparable to those used previously for the extraction of conventional inorganic mineral acids is described. A simplified phase diagram for the pentanary system comprised of H3PW12O40, HNO3, H2O, TBP, and n-octane reveals an extremely low initial concentration of H3PW12O40 (1.1 mM) at the LOC (limiting organic concentration) condition, far lower than the most effective third-phase-forming inorganic acid, namely HClO4. The results from small-angle neutron scattering (SANS) indicate that the interparticle attraction energy—U(r) calculated through application of the Baxter sticky sphere model to the SANS data at the LOC condition—does not approach the −2 k B T value associated with phase splitting in previous studies of TBP third-phase formation. The third-phase formation model based on attractive ...

The extraction of HCl by tri(2-ethylhexyl) phosphate (TEHP), tri-n-octyl phosphate (TOP), and tri-n-octylphosphine oxide (TOPO) in n-octane was investigated by liquid-liquid distribution of acid and water and small-angle neutron scattering (SANS) measurements. No formation of a heavy organic phase (third phase) was observed with TEHP and TOP under the experimental conditions used, whereas for 0.4 M TOPO the HCl limiting organic concentration (LOC) at 23°C was 0.32 M (with 5.1 M HCl in the equilibrium aqueous phase). For higher HCl concentrations in the aqueous phase, the organic phase splits into a light and a heavy layer. For TEHP and TOP, the SANS results, interpreted using the Baxter model for hard spheres with surface adhesion, indicated the formation of only small reverse micelles with little intermicellar attraction. For TOPO, the scattering signals suggested the formation of much larger and strongly interacting micelles. The critical values of the stickiness parameter, τ−1, and the interaction pote...

The molecular organization of N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide (DMDOHEMA), the current reference extractant for the DIAMEX (DIAMide EXtraction) process, is correlated with its water extraction properties from neutral media. The aggregation of DMDOHEMA in n‐heptane was investigated by vapor pressure osmometry (VPO) and the aggregate speciation characterized by combined small‐angle neutron and X‐ray scattering (SANS and SAXS, respectively). Two approaches were taken to model the aggregation of the diamide and the water extraction as a function of the diamide concentration by taking into account a single aggregation equilibrium with an average aggregation number N equal to 4.28 ± 0.05; and a competition between two types of aggregates in the organic phase, namely, aggregates of the reverse micelle type with 4 diamides per aggregate, and an oligomeric structure composed of about 10 diamide molecules which appears at high extractant concentration (>1 mol/L). In both cases, the supramolecular spe...

Aggregation phenomena in n-alkane solutions of di-n-hexylphosphoric acid (HDHP), N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), and their mixtures, were investigated by electrospray ionization–mass spectrometry (ESI-MS), vapor pressure osmometry (VPO), and small-angle X-ray and neutron scattering (SAXS and SANS). The objective of the study was to probe the formation of mixed HDHP-DMDOHEMA species before and after extraction of trivalent lanthanide and actinide (M3+) nitrates. The most important species formed by HDHP upon metal extraction has the composition M(DHP)3(HDHP)3(H2O). These species exist as spherical aggregates of the reverse micelle type with a polar core diameter of ∼ 7 A and total diameter of ∼ 11 to ∼ 15 A. The aggregation of DMDOHEMA is a progressive phenomenon, with an average aggregation number of ∼ 2 in the 0.2 to 0.6 M range and larger aggregates forming at higher concentrations. The metal loaded DMDOHEMA aggregates can be considered as interacting spheres with a ...

Small‐angle neutron scattering (SANS) data for n‐octane solutions of TBP loaded with progressively larger amounts of HNO3, HClO4, H2SO4, and H3PO4 up to and beyond the LOC (limiting organic concentration of acid) condition, were interpreted using the Baxter model for hard spheres with surface adhesion. The coherent picture of the behavior of the TBP solutions derived from the SANS investigation discussed in this paper confirmed our recently developed model for third phase formation. This model analyses the features of the scattering data in the low Q region as arising from van der Waals interactions between the polar cores of reverse micelles. Our SANS data indicated that the TBP micelles swell when acid and water are extracted into their polar core. The swollen micelles have critical diameters ranging from 15 to 22 A, and polar core diameters between 10 and 15 A, depending on the specific system. At the respective LOC conditions, the TBP weight‐average aggregation numbers are ∼4 for HClO4, ∼6 for H2SO4, ...

Cyanex 301®, di(2,4,4‐trimethylpentyl) dithiophosphinic acid, has been combined with gelatin and alginate to prepare a stable emulsion that can be used for the reactive precipitation of palladium (metal reaction with the sulfur functional group of Cyanex 301). The ionotropic gelation of alginate leads to material precipitation. The process has been successfully tested for Pd binding from 0.1–5 M HCl solutions. The maximum binding capacity was found to be close to 350 mg Pd g−1 Cyanex 301. A 1∶1 stoichiometric relation between Cyanex 301 and Pd has been identified. Extractant dependency plots showed that the ligand in the Pd‐Cyanex 301 complex can also have a solvation number higher than one. Palladium uptake is not significantly affected by the presence of competing metals such as Cu, Ni, Zn, or Pt. Quantitative stripping of Pd from the precipitated bio‐polymer could not be achieved.

The extraction of HNO3, HClO4, H2SO4 and H3PO4 by 20% (v/v) TBP (0.73 M) in n‐octane was measured under identical conditions up to and beyond the critical point of third phase formation (Limiting Organic Concentration, or LOC condition). The data, together with those obtained previously for HCl, allowed us to establish the following lyotropic series of effectiveness with respect to third phase formation in the extraction of acids by TBP: HClO4>H2SO4>HCl>H3PO4>HNO3. This series correlates with the amount of water present into the organic phase at the point of phase splitting. This result reinforces the validity of the reverse micellar model developed previously for the extraction of metal salts by TBP. The measurements of LOC values as a function of temperature revealed major differences among the acid‐TBP systems investigated. For HClO4, the strong increase of the LOC value with increasing temperatures is accompanied by a large favorable entropy change. The opposite is true for HCl, while H2SO4 a...

The conditions for reverse-micelle formation were studied for solutions of tetra-n-octyldiglycolamide (TODGA) in alkane diluents equilibrated with aqueous solutions of nitric or hydrochloric acids in the presence and absence of Nd3+. Small-angle neutron scattering, vapor-pressure osmometry, and tensiometry are all consistent with the partial formation of TODGA dimers at the lowest acidities, transitioning to a polydisperse mixture containing TODGA monomers, dimers, and small reverse-micelles of TODGA tetramers at aqueous nitric acid acidities of 0.7 M or higher in the absence of Nd. Application of the Baxter model to the samples containing 0.005-0.015 M Nd reveals the persistence of tetrameric TODGA reverse-micelles with significant interparticle attraction between the polar cores of the micelles that increases with increasing organic phase concentrations of acid or Nd. Our experimental findings suggest that the peculiar behavior of TODGA with respect to the extraction of trivalent lanthanide and actinide cations arises from the affinity of these metal cations for the preformed TODGA reverse-micelle tetramers.

Third phase formation in the extraction of Pu(IV) nitrate by 30% tri‐n‐butyl phosphate (TBP) dissolved in n‐dodecane or in the highly branched diluent hydrogenated polypropylene tetramer (HPT), which may also be known as 4,4 dipropyl heptane or tetrapropylene hydrogene, was investigated through small‐angle neutron scattering (SANS) measurements. The SANS data were interpreted using the Baxter model for hard‐spheres with surface adhesion. According to this model, the increase in scattering intensity observed when increasing amounts of Pu(NO3)4 are extracted into the organic phase, is due to interactions between small reverse micelles containing three to five TBP molecules. In n‐dodecane, the micelles interact through attractive forces between their polar cores with a potential energy of up to −2.6 kBT. This strong intermicellar attraction leads to organic phase splitting with the separation of most of the solutes of the original organic phase into a distinct phase containing interspersed layers of...

P,P′‐dialkyl methylenebisphosphonic acids are powerful metal extraction reagents exhibiting strong affinity for a variety of metal ions, especially lanthanides and actinides. While the affinity of gem‐bisphosphonic acids is generally high for most metal ions because of their relative high acidity and ability to form six‐member chelate rings, the selectivity often is low. Thus, a strategy of incorporating soft‐donor atoms such as sulfur into gem‐bisphosphonic acids has been adopted to obtain enhanced metal selectivity while retaining high extraction efficiency. To this end a new class of sulfur‐containing gem‐bisphosphonic acid solvent extraction reagents was designed, synthesized, and evaluated for heavy element separations. Specifically, the novel sulfur‐containing P,P′‐di(2‐ethylhexyl) methylenebisthiophosphonic acid, H2DEH[MBTP], was synthesized, characterized and its aggregation, metal extraction and acid‐base behavior assessed. Vapor phase osmometry measurements indicate that H2DEH[MBTP] is ...

Third phase formation in the extraction of HCl by triisobutyl phosphate (T‐iso‐BP) and tri‐sec‐butyl phosphate (T‐sec‐BP) has been investigated and compared with the tri‐n‐butyl phosphate (T‐n‐BP) system. The three TBP isomers exhibit comparable affinities for HCl, but the branched isomers extract much more water than the linear one. For T‐sec‐BP, the LOC (limiting HCl organic concentration) is characterized by much lower HCl concentrations both in the organic and aqueous phase than for the other isomers. SANS data for T‐iso‐BP and T‐sec‐BP organic phases loaded with progressive amounts of HCl have been interpreted using the Baxter model for hard spheres with surface adhesion. The critical values of the stickiness parameter, τ−1, and the interaction potential energy, U(r), are slightly different and characteristic for each of the extractants. Their values are consistent with the expectation derived from the micellar interaction model. The submitted manuscript has been created by the University of...

P,P′‐dialkyl alkylenebisphosphonic acids are powerful metal extraction reagents. The acid dissociation constants for a homologous series of aqueous‐insoluble P,P′‐di‐3‐(trimethylsilyl)‐propyl and aqueous‐soluble P,P′‐diethyl methylene‐, ethylene‐ and propylene‐ bisphosphonic acids were determined in a 70∶30 w/w methanol‐water solvent by potentiometric titration and 31P NMR spectrometry. The values obtained for the diethyl‐substituted acids were compared with those determined in water and used to assess the effect of the medium on the aqueous acid dissociation constants of the lipophilic series of P,P′‐di‐3‐(trimethylsilyl)propyl alkylenebisphosphonic acids. The dependence of the organic/aqueous distribution equilibrium on the aqueous acid concentration was also investigated using electrospray ionization mass spectrometry. The acid dissociation and organic/aqueous distribution properties of the substituted alkylenebisphosphonic acids are discussed in terms of their influence on metal ion extractio...

Third phase formation in the extraction of HCl by tri‐n‐butyl phosphate (TBP) in n‐octane has been investigated. The extraction of the acid is accompanied by the simultaneous extraction of large amounts of water and brings about organic phase splitting when the equilibrium HCl concentration in the aqueous phase is higher than 7.6 M. For a description of mechanism and energetics of these phenomena, a combination of coordination chemistry and concepts and techniques that are typical of colloid chemistry is needed. SANS data for organic phases loaded with progressive amounts of HCl and water have been interpreted using the Baxter model for hard spheres with surface adhesion. According to this model, the increase in scattering intensity in the low Q range observed when increasing amounts of solutes are extracted into the organic phase, arises from van der Waals interactions between reverse micelles containing up to seven TBP molecules. At the onset of third phase formation, the potential energy of at...

Fluorinated alcohols are being used as diluent modifiers for the selective extraction of cesium from caustic media by calixarene‐crown ethers. Previous work has established the equilibria taking place in solution during cesium extraction and the stoichiometry of the complexes formed in the organic phase, but the aggregation behaviour of the modifiers remains to be precisely understood. Therefore, vapour pressure osmometry experiments were carried out to gain further insight. The aggregation state of a variety of fluorinated and non‐fluorinated alkylphenoxy alcohols and 1‐decanol in n‐heptane, was determined at 25°C. These alcohols were found to form aggregates containing between three and five (most frequently four) molecules. Introduction of these independently investigated aggregation equilibria for the solvent modifiers in the data modeling improved the ability of our extraction model to correctly predict metal distribution ratios.

The dialkyl‐substituted diphosphonic acids are powerful solvent extraction reagents for actinide separation and preconcentration from biological, environmental, and nuclear waste samples. In spite of the intensive scrutiny of the solvent extraction properties of these compounds, only the extraction of Eu(III) and Am(III), among the lanthanides and trivalent actinides, has been investigated thus far. In this work, we report the extraction of all members of the lanthanide series, plus lanthanum, yttrium, Am(III), Cm(III), and Cf(III), by two representative diphosphonic acids [i.e., P,P′‐di(2‐ethylhexyl) methylenediphosphonic acid (H2DEH[MDP]) and the P,P′‐di(2‐ethylhexyl) ethylenediphosphonic acid (H2DEH[EDP])]. H2DEH[MDP] shows very efficient extraction of all ions investigated, but little selectivity, except for the heaviest lanthanides. H2DEH[EDP], on the other hand, exhibits less efficient extraction, but much higher selectivity, with an average separation factor between contiguous elements of ...

Symmetrically substituted partial alkyl‐esters of methylenediphosphonic acid are powerful metal ion extractants for actinides in all oxidation states. A preliminary study of calcium and americium(III) extraction by the n‐octyl and 2‐ethylhexyl di‐substituted esters of methylenediphosphonic acid revealed the distribution ratios and the nitric acid dependency behaviors for the two extractants to be very similar, with the extraction efficiency for the n‐octyl ester somewhat higher than for the 2‐ethylhexyl derivative. Since the basicity of the phosphoryl groups in the two extractants should be essentially the same, the differences in the solvent extraction efficiency of these two C8‐alkyl‐substituted ligands could arise from differences in the steric requirements of the ester groups. Ester group steric effects on metal ion extraction for a series of symmetrically alkyl‐substituted partial esters and identically substituted tetra‐esters of methylenediphosphonic acid were investigated to gain insight ...

Small-angle neutron scattering (SANS) data for the tri-n-butyl phosphate (TBP)-n-octane, HNO(3)-Zr(NO(3))(4) solvent extraction system, obtained under a variety of experimental conditions, have been interpreted using the Baxter model for hard spheres with surface adhesion. The increase in scattering intensity in the low Q range observed when increasing amounts of Zr(NO(3))(4) were extracted into the organic phase was interpreted as arising from interactions between small reverse micelle-like particles containing two to three TBP molecules. Upon extraction of Zr(NO(3))(4), the particles interact through attractive forces between their polar cores with a potential energy that exceeds 2 k(B)T. The interparticle attraction, under suitable conditions, leads to third phase formation. A linear relationship exists between the derivative of the potential energy of attraction with respect to the concentration of nitrate ions in the organic phase and the ionization potential or the hydration enthalpy of the extracted metal cations.

Small-angle neutron scattering (SANS) data for the tri-n-butyl phosphate (TBP)−n-dodecane, HNO3−UO2(NO3)2 solvent extraction system have been interpreted using the Baxter model for hard spheres with surface adhesion. The increase in the scattering intensity in the low Q range observed when increasing amounts of HNO3 or UO2(NO3)2 are transferred into the organic phase has been interpreted as arising from interactions between solute particles. The SANS data have been reproduced using a 12−16 A diameter of the hard sphere, dhs, and a 5.6kBT−7.1kBT stickiness parameter, τ-1. When in contact with an aqueous phase, TBP in n-dodecane forms small reverse micelles containing three TBP molecules. Upon extraction of water, HNO3, and UO2(NO3)2, the swollen micelles interact through attractive forces between their polar cores with a potential energy of about 2kBT and an effective Hamaker constant of about 4kBT. The intermicellar attraction, under suitable conditions, leads to third-phase formation. Upon phase splittin...

Partially esterified alkylenediphosphonic acids were shown to be effective solvent extraction reagents for the removal of actinide cations from acidic aqueous solutions into conventional organic solvents. As a first step in an effort to design diphosphonic acid extractants that are soluble in supercritical carbon dioxide, we prepared and characterized a novel series of silyl-substituted alkylenediphosphonic acids. The aggregation of these extractants in toluene at 25°C was studied by vapor pressure osmometry. Their solvent extraction chemistry was investigated by employing radiotracers to determine the distribution ratios for selected metal ions between an acidic aqueous phase and an organic phase containing the diphosphonic acid extractant. To determine the effect of incorporating a silicon functionality into diphosphonic acids, the aggregation and solvent extraction properties of the silyl-substituted alkylenediphosphonic acids were compared with those of the conventional alkyl-substituted di(2-ethylhex...

Formation of a third organic phase at high metal loading in the extraction of tetravalent actinides by TBP in aliphatic diluents has been investigated mostly from the standpoint of the composition of the organic phase species before and after phase splitting. Very little is known of the structure and morphology of the organic phase species. In this work, a study of third phase formation upon either dissolution of Th(NO3)4 in 20% TBP in n-octane or Th(NO3)4 extraction from 1 M HNO3 by 20% TBP in n-octane is reported. Chemical analyses have shown that, under the conditions of this work, Th(IV) exists in the organic phase mainly as the trisolvate Th(NO3)4·(TBP)3. The third phase species also contains a small amount of HNO3, presumably hydrogen-bonded to the trisolvate complex. Small-angle neutron scattering measurements on TBP solutions loaded with only HNO3 or with increasing amounts of Th(IV) revealed the presence, before phase splitting, of large ellipsoidal aggregates with the parallel and perpendicular ...

In spite of its technological importance, third phase formation in the extraction of hexavalent actinides from nitric acid solutions into alkane solutions of tri-n-butylphosphate (TBP) has received only limited attention. The focus of the few available literature works has been primarily centered on the composition of the third phase and on the stoichiometry of the metal complexes. Very little is known, on the other hand, about the structure and morphology of the third phase species of hexavalent actinides. In the present investigation, the formation of a third phase upon extraction of U(VI) by 20% TBP in deuterated n-dodecane from nitric acid solutions was studied. Chemical analyses have shown that U(VI) exists in the third phase as a species having the composition UO2(NO3)2·(TBP)2·HNO3. Small-angle neutron scattering measurements on TBP solutions loaded with only HNO3 or with increasing amounts of U(VI) have revealed the presence, both before and after phase splitting, of relatively large ellipsoidal ag...

Solvent extraction reagents containing the diphosphonic acid group exhibit extraordinary affinity for tri-, tetra-, and hexavalent actinides. Use of these reagents has been proposed for actinide separation and preconcentration procedures. A new extractant, P,P′-di(2-ethylhexyl) benzene-1,2-diphosphonic acid (H2DEH[1,2-BzDP]), has been synthesized. Its metal extraction characteristics are reported and compared to the previously synthesized P,P′-di(2-ethylhexyl) methylene-(H2DEH[MDP]), ethylene-(H2DEH[EDP]), and butylene-(H2DEH[BuDP]) diphosphonic acids. Different degrees of aggregation and different extraction mechanisms and stoichiometries have been reported for these ligands. In this work, thermodynamic parameters associated with the extraction of selected metal ions by these ligands were measured to provide further insight into the mechanism of the extraction processes involved. Knowledge of the enthalpy, entropy, and free-energy changes, in combination with other fundamental principles governing extrac...

The synergistic extraction of alkaline earth (Ca2+, Sr2+, Ba2+ and Ra2+) and actinide (Am3+, UO2 2+ and Th4+) cations from aqueous nitric acid solutions by mixtures of P,P′-di(2-ethylhexyl) methylene-(H2DEH[MDP]), ethylene-(H2DEH[EDP]), and butylene-(H2DEH[BuDP]) diphosphonic acids and neutral extractants in o-xylene has been investigated. The cis-syn-cis and cis-anti-cis stereoisomers of dicyclohexano-18-crown-6 (DCH18C6), the unsubstituted 21-crown-7 (21C7) and dicyclohexano-21-crown-7 (DCH21C7) were used as neutral synergists of the crown ether type. For Am(III) synergistic effects were also investigated using neutral organophosphorus esters, such as, tri-n-butylphosphate (TBP), diamyl amylphosphonate (DA[AP]) and tri-n-octylphosphine oxide (TOPO) as co-extractants. In all systems investigated, no synergistic extraction enhancement was observed for actinide ions. For the alkaline earth cations, synergistic effects were only observed when mixtures of H2DEH[EDP] or H2DEH-[BuDP] with DCH18C6 were...

The infrared reflectance spectra of the third phases formed in the systems UO2(NO3)2/HNO3/20%TBP in n-dodecane and Th(NO3)4/HNO3/20%TBP in n-octane gave evidence for the presence in solution of a significant amount of weakly bonded molecular nitric acid. From the correlation between the ratio of the areas of the bands at 1672 cm−1 and 1648 cm−1, characteristic of weakly intermolecularly hydrogen-bonded nitric acid and nitric acid strongly bonded to TBP, respectively, the molecular HNO3 concentration was determined. The presence of these two bands in the spectra of the third phase samples provides evidence that only part of the HNO3 is directly and strongly bound to the TBP phosphoryl group. The ratio of the weakly intermolecularly hydrogen-bonded HNO3 to that bound directly to P=O group of TBP was much higher for the uranium than for the thorium third phases formed under comparable conditions. The estimated amounts of the weakly intermolecularly hydrogen-bonded HNO3 were about 47% and 30% of the ...

In an ongoing effort to determine the relationship between structure and function in diphosphonic acids, the aggregation and solvent extraction chemistry of four novel silicon-substituted diphosphonic acids, P,P′-di[3-(trimethylsilyl)-1-propyl] propylene- (H2DTMSP[PrDP]), butylene- (H2DTMSP[BuDP]), pentylene- (H2DTMSP[PDP]), and hexylene diphosphonic acid (H2DTMSP[HDP]), were investigated. Vapor pressure osmometry indicates that H2DTMSP[PrDP] and H2DTMSP[PDP] are dimeric in toluene at 25°C, while H2DTMSP[BuDP] and H2DTMSP[HDP] are primarily trimeric and hexameric, respectively. The solvent extraction of selected alkaline earth cations (Ca, Sr, and Ba) and representative tri-, tetra-, and hexavalent actinides [Am(III), Th(IV), and U(VI)], from nitric acid solutions into o-xylene solutions of the ligands has been studied and compared to results reported previously for some analogous di(2-ethylhexyl)-substituted diphosphonic acids. Differences observed in the magnitude of distribution ratios, based on the nu...

A new acidic organophosphorus extractant, P,P′-di(2-ethylhexyl) benzene-1,2-diphosphonic acid (H2DEH[1,2-BzDP]), has been synthesized. Though the extractant proved unstable with respect to acid hydrolysis upon storage at room temperature, it was sufficiently stable in o-xylene solution under refrigeration to determine its aggregation and extraction properties for Sr2+ and Am3+ between 25 and 60°C. Slope analysis of radioanalytical data and the results of osmometric measurements indicate that the dominant extraction reaction for both metal ions is M n++n HL⇋ML n +n H+ where n=2 for Sr(II) and 3 for Am(III). In the Sr system there is also evidence for the extraction of SrNO3 +. As the extractant aggregation and extraction stoichiometries do not change significantly with temperature, it was possible to derive enthalpies and entropies of extraction from the temperature dependence of the metal extraction equilibrium constants between 25.0 and 60.0°C. The extraction of both metal ions is driven by an e...

In conjunction with efforts to develop novel actinide extractants that exhibit solubility in supercritical carbon dioxide (SCCO2), the effect of adding silicon-based functionalities to diphosphonic acids on their aggregation and solvent extraction chemistry was investigated. Two silyl-derivatized diphosphonic acids, P,P′-di[3-(trimethylsilyl)-1-propylene] methylenediphosphonic acid (H2DTMSP[MDP]) and P,P′-di[3-(trimethylsilyl)-1-propylene] ethylenediphosphonic acid (H2DTMSP[EDP]), were prepared and their aggregation and metal ion extraction properties compared to those of the previously studied P,P′-di(2-ethylhexyl) alkylenediphosphonic acids. Vapor pressure osmometry of H2DTMSP[MDP] and H2DTMSP[EDP] in toluene (25°C) indicates that, as is the case for the 2-ethylhexyl-substituted alkylenediphosphonic acid analogs, the compounds are dimeric and (primarily) hexameric, respectively, in the concentration range investigated. Distribution ratio measurements for the alkaline earth cations Ca2+, Sr2+, Ba2+, and ...

The extraction of Am(III) from HNO3 by o-xylene solutions of P,P′-di(2-ethylhexyl) methylene- (H2DEH[MDP]), ethylene- (H2DEH[EDP]), and butylene- (H2DEH[BuDP]) diphosphonic acids has been investigated. Thermodynamic parameters of the extraction process were determined by the temperature coefficient of the metal distribution ratio in the 25.0 to 60.0°C temperature range. The extractant aggregation and the extraction stoichiometries with the different diphosphonic acids did not exhibit any significant temperature dependence. Extraction of Am(III) by H2DEH[MDP] is favored by both enthalpy and entropy variations. When Am(III) is extracted by either H2DEH[EDP] or H2DEH[BuDP] the process is entropy controlled. The enthalpy variation for Am(III) extraction exhibited a trend along the series H2DEH[MDP], H2DEH[EDP], H2DEH [BuDP], with the reaction being exothermic for the first, thermoneutral for the second, and endothermic for the third extractant, respectively. This trend was explained as arising from the format...

Small angle neutron scattering and visible absorption spectroscopy were used to study the neodymium complexes of a series of acidic organophosphorus extractants in deuterated toluene at high (≥33% theoretical capacity) metal loading. Organic phases containing 0.10 M bis(2-ethylhexyl)phosphoric acid (HDEHP), bis(2,4,4-trimethylpentyl)oxothiophosphinic acid (HC302), or bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301) were used. Under these conditions, the neutron scattering experiments show that HDEHP and HC302 exist as dimeric species in the absence of Nd. Extraction of Nd disrupts the dimeric structure of the extractants to form dinuclear complexes with the formula Nd2(DEHP)6 or Nd2(C302)6. In contrast, 0.10 M HC301 is not dimeric in deuterated toluene. At 86% of the theoretical Nd capacity, the extracted complex is also dinuclear with the average formula Nd2(C301)6, but at 46% of the theoretical Nd capacity only the mononuclear complex, Nd(C301)3, is formed. The Nd hypersensitive transitions in th...

The preparation and characterization of a new extraction chromatographic resin exhibiting extraordinarily strong retention of hexavalent uranyl ion over a wide range of nitric acid concentrations and very high selectivity for U(VI) over Fe(III) and numerous other cations is described. This new material (designated U/TEVA-2) comprises a novel liquid stationary phase consisting of an equimolar mixture of diamyl amylphosphonate (DA[AP]) and Cyanex 923((R)) (a commercially available trialkyl-phosphine oxide, TRPO) sorbed on silanized silica or Amberchrom CG-71. Cyanex 923 is shown to be preferable to a related TRPO, Cyanex 925((R)), due to its lower viscosity and higher selectivity for U(VI) over Fe(III). The retention of uranyl nitrate by the U/TEVA-2 resin, as measured by the k' values (number of free column values to peak maximum) is >5000 from approximately 0.1 to 8 M HNO(3). The ability of the new resin to strongly and selectively retain U(VI) from such a wide range of acid concentrations, along with its favorable physical properties, make it a good candidate for application in the separation and preconcentration of U(VI) from complex environmental, biological, and nuclear waste samples for subsequent determination.

Solvent extraction reagents containing the diphosphonic acid group exhibit an extraordinary affinity for tri-, tetra-, and hexavalent actinides. Their use has been considered for actinide separation and preconcentration procedures. Solvent extraction data obtained with P,P′-di(2-ethylhexyl) methane-, ethane-, and butanediphosphonic acids exhibit features that are difficult to explain without knowl edge of the aggregation state of the extractants. Information about the aggregation of the dialkyl-substituted diphosphonic acids in aromatic diluents has been obtained using the complementary techniques of vapor pressure osmometry, small-angle neutron scattering, infrared spectroscopy, and molecular mechanics. The results from these techniques provide an understanding of the aggregation behavior of these extractants that is fully compatible with the solvent extraction data. The most important results and their relevance to solvent extraction are reviewed in this paper. The work at ANL was performed under the au...

In this work, the extraction of Am(III), U(VI), Th(IV) and Fe(III) by P,P′-di(2-ethylhexyl) methylene- (H2DEH[MDP]), ethylene- (H2DEH[EDP]), and butylene- (H2DEH[BuDP]) diphosphonic acids dissolved in the monomerizing diluent 1-decanol has been investigated. A comparison of the acid dependencies with those observed in o-xylene has revealed a number of novel features which have been ascribed to extraction of metal nitrates through a solvation mechanism made possible by facile transfer of nitrate ions into the 1-decanol phase. The use of 1-decanol as the diluent gives rise to strong suppression of metal extraction, which increases along the series Fe(III)

In this work, the extraction of Ca2+, Sr2+ and Ba2+ by P,P′-di(2-ethylhexyl) methylene- (H2DEH[MDP]), ethylene- (H2DEH[EDP]), and butylene- (H2DEH[BuDP]) diphosphonic acids, has been investigated in the monomerizing diluent 1-decanol. In all cases, the slope of the acid dependencies at low aqueous acidities equals −2, indicating that two protons are displaced from the extractant molecules, regardless of the type of complexes formed in the organic phase. Extraction of metal nitrates through a solvation mechanism, however, has also been identified. The extractant dependency data exhibit variable slopes, consistent with the simultaneous formation of complexes having 1:1 (MA) and 1:2 (MA·H2A or M(HA)2) metal to ligand stoichiometry (where A denotes the anion of the extractants). The latter species becomes predominant at higher extractant concentrations. Based on the selectivity sequences observed for the alkaline earth cations with the di(2-ethylhexyl) diphosphonic acids, probable structures have been assigne...

Infrared studies for the HNO3/0.73 M TBP n-octane system are reported. Two extracted species, TBP · HNO3 and TBP · 2HNO3, were identified in the organic phase. The concentration of the individual species was determined by the analysis of the vibrational band at ∼1650 cm−1. The band at 1648 cm−1 was assigned to the monosolvate TBP · HNO3 and the band at 1672 cm−1 to the hemisolvate TBP · 2HNO3. The infrared spectra revealed that with respect to the P═O bond, as well to each other, the HNO3 molecules in the hemisolvate are spectrally non-equivalent. The predominant structure of TBP · 2HNO3 involves the chain HNO3 dimer. Some ionic NO3 − and hydronium ions were identified in this system but only during formation of the monosolvate. The analyses performed in this system can serve for the characterization of HNO3 in related systems in the presence of metal species. *Work performed under the auspices of the office of Basic Energy Sciences, Division of Chemical Sciences, Department of Energy, under contract W-31...

The thermodynamics of extraction of U(VI) and Sr(II) from aqueous HNO3 solutions by o-xylene solutions of P,P′-di(2-ethylhexyl) methylene- (H2DEH[MDP]), ethylene- (H2DEH- [EDP]), and butylene- (H2DEH[BuDP]) diphosphonic acids has been investigated by measuring metal distribution ratios in the 25.0 to 60.0°C temperature range. The extractant aggregation and extraction stoichiometries for both metal ions did not change with temperature. The extraction of U(VI) by all three extractants is strongly driven by both enthalpy and entropy variations. The extraction of Sr(II) by H2DEH[MDP] is enthalpy driven. Unfavorable entropy changes characterize the extraction of Sr(II) by H2DEH[EDP] and H2DEH[BuDP]. This is not indicative of the micellar-type extraction mechanism exhibited by Am(III). A more rigorous thermodynamic treatment of previously reported Am(III) data has been performed. The absolute values of the free energy and entropy changes of the extraction are affected. However, the extraction of Am(III) by H2DE...

This paper provides a comprehensive review of synergistic solvent extraction using crown ethers with a focus on the role of both extractants in facilitating cation-specific separations. An introduction to the various equilibria affecting synergistic extraction using crown ethers is followed by a review of the work published in this field during the 1972-1999 time period. The influence of various solvent extraction parameters on the potential for cation-selective synergism is critically examined. Those synergistic extractant combinations showing cation selectivity are highlighted, as are the fundamental investigations that are the foundation of the current understanding of synergistic solvent extraction using crown ethers.

Fundamental investigations of solvent extraction and ion exchange separations of radioactive materials have been conducted within the National Laboratory system of the U. S. Department of Energy (and its predecessor agencies) for the past 50 years. Basic research conducted at Oak Ridge and Argonne National Laboratories has produced both high quality new science and important applications in nuclear technology. The present contribution is an attempt to summarize the most important scientific results arising from this research during the past 10 years, a time of great change in the nuclear separations field, and to suggest possible directions for the next stage of research and development in this field.

Deuterated toluene solutions of di-n-octylphosphoric acid, HDOP, containing Sr+ extracted from 0.1 M LiNO3 aqueous solutions, were investigated by small angle neutron scattering (SANS). The extractions were also performed in the presence of either the cis-syn-cis or the cis-anti-cis stereoisomer of dicyclohexano-18-crown-6 (DCH18C6) in combination with HDOP in the toluene phase. The addition of the crown ether increased metal extraction into the organic phase over that observed with HDOP alone (synergistic extraction), The cis-syn-cis isomer was more effective than the cis-anti-cis isomer in enhancing Sr(II) extraction in the synergistic system. The SANS results confirmed that when the metal cation is extracted by HDOP present in large stoichiometric excess, the predominant species formed in the organic phase can be described as Sr(H(DOP)2)2 with 2 extra HDOP molecules solvating the complex. In the synergistic crown ether-HDOP system, the SANS data are consistent with solvent extraction data sugg...

The effect of 60Co irradiation on the Diphonix™, Diphosil and Diphonix-CS chelating ion exchange resins, and on two Dipex™ extraction chromatographic resins containing the P,P’-di(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP]) impregnated in the pores of a polymeric support (Dipex-1) and of silica (Dipex-2), respectively, has been investigated. The resins have been irradiated while in contact with HNO3 (Diphonix, Diphosil and Dipex resins) or NaOH (Diphonix-CS resin) up to an absorbed dose of about 200 Mrad. As a probe of the resin radiolytic degradation, metal uptake (both equilibrium and kinetics) and capacity measurements have been performed. Our results show that the Diphonix-CS resin properties are practically unaffected by irradiation under the experimental conditions used in this work. The Diphonix, Diphosil, and especially the Dipex resins suffer substantial capacity losses, but their affinity for actinide ions is not seriously compromised. On the other hand, the kinetics of metal up...

The aggregation of several metal complexes formed during solvent extraction with P,P'-di(2-ethylhexyl) ethanediphosphonic acid, H2DEH[EDP], and by P,P'-di(2-ethylhexyl) butanediphosphorac acid, H2DEH[BuDP], in deuterated toluene, has been investigated by small angle neutron scattering (SANS). With H2DEH[EDP], the extraction of Ca(II), La(IH) and U(VT) does not disrupt the cyclic hexameric structure of the ligand in solution. Fe(III) and Th(IV) complexes of H2DEH[EDP], on the other hand, exhibit a very modest tendency to aggregate but only at very high metal loading in the organic phase. With H2DEH[BuDP], the extraction of Ca(H), La(III), U(VI) and Th(IV) is not accompanied by significant aggregation of the metal complexes The Fe(HI)-H2DEH[BuDP] complexes, however, form long cylindrical aggregates similar to those previously observed with P,P'di(2-ethylhexyl) methanediphosphonic acid, H2DEH[MDP]. The aggregation behavior of the various metal-extractant species is discussed in light of the informat...

Hydrogen bonding of dialkyl-substituted diphosphonic acids in nonpolar (toluene and CCl{sub 4}) and alcohol (1-decanol) solutions is examined. The compounds are monomeric in 1-decanol and dimeric or higher in nonpolar organic diluents. Infrared spectroscopy and molecular mechanics calculations suggest that the dimers of P,P{prime}-di(2-ethylhexyl) methanediphosphonic acid (H{sub 2}DEH[MDP]) and its straight-chain isomer, P,P{prime}-dioctyl methanediphosphonic acid (H{sub 2}DO[MDP]), adopt rigid highly hydrogen-bonded structures such as C or D. The homologous P,P{prime}-di(2-ethylhexyl) ethane- and butanediphosphonic acids, H{sub 2}DEH[EDP] and H{sub 2}DEH[BuDP], respectively adopt structures that are also intermolecularly hydrogen-bonded but more flexible. The effect on the P+O stretching vibration of increasing 1-decanol concentration in the solvent differs for these compounds. In the case of H{sub 2}DEH[MDP] and H{sub 2}DO[MDP], the frequency remains constant until all CCl{sub 4} has been replaced by the alcohol, then the P=O stretching frequency shifts to a lower energy. In the case of H{sub 2}DEH[edp] and H{sub 2}DEH[BuDP], a gradual shift to higher energy occurs as the alcohol concentration increases. The magnitude of the difference in the P=O stretching frequencies between CCL{sub 4} and 1-decanol solution is greatest for organophosphonic acids, less for organodiphosphonic acids, and least for organophosphoric acids.

The partitioning of Ca(II), Sr(II), and Ba(II) in solvent extraction systems comprising di-n-octylphosphoric acid (HDOP) and individual stereoisomers of dicyclohexano- 18-crown-6 (DCH18C6) in tolue...

The effect of three water-soluble, unsubstituted crown ethers (15-crown-5 (15C5), 18-crown-6 (18C6) and 21-erown-7 (21C7) on the uptake of Ca, Sr, Ba and Ra cations by a sulfonic acid cation exchange resin, and on the extraction of the same cations by xylene solutions of dinonylnaphthalenesulfonic acid (HDNNS) from aqueous hydrochloric acid solutions has been investigated. The crown ethers enhance the sorption of the larger cations by the ion exchange resin, thereby improving the resin selectivity over calcium, a result of a synergistic interaction between the crown ether and the ionic functional groups of the resin. Similarly, the extraction of the larger alkaline earth cations into. xylene by HDNNS is strongly synergized by the presence of the crown ethers in the aqueous phase. Promising results for intra-Group IIa cation separations have been obtained using each of the three crown ethers as the aqueous ligands and the sulfonic acid cation exchange resin. Even greater separation factors for the...

The aggregation of several metal complexes formed during solvent extraction with P,P'-di(2-ethylhexyl) methanediphosphonic acid, H2DEH[MDP], in deuterated toluene, has been investigated by small angle neutron scattering (SANS). The SANS results show that the Ca(II)-, Al(ni)-, La(III)- and Nd(III)-H2DEH[MDP] compounds exhibit little or no tendency to aggregate. Uranyl complexes of H2DEH[MDP] at high metal loading form small aggregates with an aggregation number of approximately 14. This behavior is in sharp contrast with the Th(IV)-H2DEH[MDP] system which forms large aggregates in the organic phase under high metal loading conditions. The aggregation behavior of the various metal-H2DEH[MDP] compounds is discussed in light of the information obtained from earlier solvent extraction, vapor pressure osmometry, and infrared spectroscopy studies.