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Lemire D, Dumas T, Guillaumont D, Solari PL, Menut D, Giusti F, Arrachart G, Dourdain S, Pellet-Rostaing S. Molecular and Supramolecular Study of Uranium/Plutonium Liquid-Liquid Extraction with N, N-Dialkylamides. Inorg Chem 2024; 63:18809-18819. [PMID: 39311664 DOI: 10.1021/acs.inorgchem.4c02880] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/08/2024]
Abstract
In the context of the separation of uranium and plutonium from spent fuel allowed by N,N-dialkylamides, three regioisomers of N,N-di(2-ethylhexyl) butyramide (DEHBA or ββ) and the diastereopure isomers of N-(2-ethylhexyl)-N-(oct-3-yl)butyramide (EHOBA or αβ) were synthesized to assess their extraction performance and to study the mechanisms at the origin of the differences observed between the stereo- and regioisomers. The N,N-dialkylamides showed differences in extraction, with a greater effect of regio- than stereoisomerism. A mechanistic study at both the molecular and supramolecular scales was initially applied to explain these effects. X-ray absorption and UV-vis spectroscopy showed that uranium is extracted by a UO2(NO3)2L2 complex, which is not very sensitive to steric hindrance, while plutonium is extracted by two complexes, Pu(NO3)4L2 and Pu(NO3)6(HL)2, which are differently affected by stereo- and regioisomerism. Investigations at the supramolecular scale also showed that Pu(NO3)4L2 complexes are disadvantaged by the bulkiness of the extractants, while Pu(NO3)6(HL)2 is favored by the preformation of larger supramolecular aggregates.
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Affiliation(s)
- David Lemire
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Marcoule 30207, France
| | - Thomas Dumas
- CEA, DES, ISEC, DMRC, Univ Montpellier, Marcoule 30207, France
| | | | - Pier Lorenzo Solari
- Synchrotron SOLEIL, MARS beamline, l'Ormes des Merisiers, Départemental 128, Saint-Aubin 91190, France
| | - Denis Menut
- Synchrotron SOLEIL, MARS beamline, l'Ormes des Merisiers, Départemental 128, Saint-Aubin 91190, France
| | - Fabrice Giusti
- ICSM, Univ Montpellier, CNRS, CEA, ENSCM, Marcoule 30207, France
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George J, Salcedo R, Greenberg R, Elshendidi H, McGregor D, Burton-Pye B, Francesconi LC, Paulenova A, Gelis AV, Poineau F. Structural Investigation of Technetium Dibutylphosphate Species Using X-ray Absorption Fine Structure Spectroscopy. Inorg Chem 2023; 62:16378-16387. [PMID: 37751567 DOI: 10.1021/acs.inorgchem.3c02010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/28/2023]
Abstract
The speciation of Tc after the extraction of Tc(IV) from H2O and 1 M HNO3 by dibutylphosphoric acid (HDBP) in dodecane has been studied by X-ray absorption fine structure (XAFS) spectroscopy. Results show the formation of dimeric species with Tc2O2 and Tc2O units, and the formulas [Tc2O2(DBP·HDBP)4] (1) and [Tc2O(NO3)2(DBP)2(DBP·HDBP)2] (2) were, respectively, proposed for the species extracted from H2O and 1 M HNO3. The interatomic Tc-Tc distances found in the Tc2O2 and Tc2O units [2.55(3) and 3.57(4) Å, respectively] are similar to the ones found in Tc(IV) dinuclear species. It is likely that the speciation of Tc(IV) in dodecane is due to the extraction of a species with a Tc2O unit for (2) and to the redissolution of a Tc(IV)-DBP solid for (1). The XAFS results for (1) and (2) were compared to that obtained for the extraction of Tc(IV) with TBP/HDBP/dodecane from 0.5 M HNO3, (3) which highlight the formation of Tc mononuclear nitrate species {i.e., [Tc(NO3)3(DBP)] or [Tc(NO3)2(DBP·HDBP)]}. These results confirm the importance of the preparation and speciation of the Tc(IV) aqueous solutions prior to extraction and how much this influences and drives the final Tc speciation in organic extraction. These studies outline the complexity of Tc separation chemistry and provide insights into the behavior of Tc during the reprocessing of used nuclear fuel.
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Affiliation(s)
- Jonathan George
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S.Maryland Parkway, Las Vegas, Nevada 89154, United States
| | - Ramsey Salcedo
- Ph.D. Program in Chemistry, Graduate Center of the City University of New York, New York, New York 10016, United States
- Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10065, United States
- Lehman College of the City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468, United States
| | - Rachel Greenberg
- Ph.D. Program in Chemistry, Graduate Center of the City University of New York, New York, New York 10016, United States
- Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10065, United States
- Lehman College of the City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468, United States
| | - Hossam Elshendidi
- Ph.D. Program in Chemistry, Graduate Center of the City University of New York, New York, New York 10016, United States
- Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10065, United States
- Lehman College of the City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468, United States
| | - Donna McGregor
- Ph.D. Program in Chemistry, Graduate Center of the City University of New York, New York, New York 10016, United States
- Lehman College of the City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468, United States
| | - Benjamin Burton-Pye
- Ph.D. Program in Chemistry, Graduate Center of the City University of New York, New York, New York 10016, United States
- Lehman College of the City University of New York, 250 Bedford Park Boulevard West, Bronx, New York 10468, United States
| | - Lynn C Francesconi
- Ph.D. Program in Chemistry, Graduate Center of the City University of New York, New York, New York 10016, United States
- Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10065, United States
| | - Alena Paulenova
- Department of Nuclear Engineering and Radiation Health Physics, 100 Radiation Center, Oregon State University, Corvallis, Oregon 97331-5903, United States
| | - Artem V Gelis
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S.Maryland Parkway, Las Vegas, Nevada 89154, United States
| | - Frederic Poineau
- Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S.Maryland Parkway, Las Vegas, Nevada 89154, United States
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Importance of weak interactions in the formulation of organic phases for efficient liquid/liquid extraction of metals. Curr Opin Colloid Interface Sci 2020. [DOI: 10.1016/j.cocis.2020.03.004] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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4
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Jackson A, Nilsson M. Synergism and Aggregation in Multi-Extractant Solvent Extraction Systems. SOLVENT EXTRACTION AND ION EXCHANGE 2019. [DOI: 10.1080/07366299.2019.1639367] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Andy Jackson
- Department of Chemical Engineering and Materials Science, University of California Irvine, Irvine, CA, USA
| | - Mikael Nilsson
- Department of Chemical Engineering and Materials Science, University of California Irvine, Irvine, CA, USA
- Department of Chemistry, University of California Irvine, Irvine, CA, USA
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5
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Bapat DU, Dalvi VH. Molecular Insights into Water Clusters Formed in Tributylphosphate-Di-(2-ethylhexyl)phosphoric Acid Extractant Systems from Experiments and Molecular Dynamics Simulations. J Phys Chem B 2019; 123:1618-1635. [PMID: 30730739 DOI: 10.1021/acs.jpcb.8b10831] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Di-(2-ethylhexyl)phosphoric acid (D2EHPA) and tributylphosphate (TBP) are two of the most studied and researched organophosphorous extractants. D2EHPA is an acidic extractant, offering both hydrogen bond donor and acceptor sites while TBP, a neutral extractant, only offers a single acceptor site per molecule. In spite of this, it is observed that 1 M D2EHPA in dodecane is a poorer extractant for water than 1 M TBP in dodecane. The objective of present work is to look into the molecular interactions that cause such behavior. Experiments were carried out with varying molar ratios of TBP and D2EHPA in the organic dodecane phase. Total extractant concentration was kept constant at 1 M with dodecane as diluent. Water extraction was quantified by measuring the moisture content of the organic phase after equilibration. 1H and 31P NMR spectra of the organic phase samples were recorded to study the change in the chemical environment upon extraction. Small angle X-ray scattering data of water saturated extractant phases were analyzed for the possibility of a reverse micellar aggregate formation. Molecular dynamics simulations could calculate free energies in quantitative agreement with experiments. Experimental and simulation studies showed that aggregation in the organic phase was promoted by the presence of water. This combined approach, of experiments and simulation, has shown that water is indispensable for the formation of ordered aggregates of extractants in nonpolar organic solvents. It is seen that, in the organic phase, around 80% of water's hydrogen bonds are with extractant molecules rather than with itself. The analysis clearly indicates that, rather than forming an aqueous core surrounded by extractant, water acts as a bridge between extractant molecules.
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Affiliation(s)
- Deepak U Bapat
- Department of Chemical Engineering , Institute of Chemical Technology , Mumbai 400019 , India
| | - Vishwanath H Dalvi
- Department of Chemical Engineering , Institute of Chemical Technology , Mumbai 400019 , India
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Yoo T, Nguyen HD, Nilsson M. Molecular Dynamics Investigations of Dibutyl-phosphoric Acid-Parameterization and Dimerization. J Phys Chem B 2018; 122:12040-12048. [PMID: 30431277 DOI: 10.1021/acs.jpcb.8b07559] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A reparameterized molecular dynamics force field for dibutyl-phosphoric acid (HDBP) has been developed. Parameterization was done using the general Amber force field, as a starting point. The density and dipole moment of bulk phase simulations compare well to that of known experimental values, and the heat of vaporization is comparable to an estimated empirical value. All values have been optimized to within 4%. The newly optimized force field was validated against the self-diffusion coefficient, matching experimental data to within 18%, which is a significant improvement compared to the nonoptimized force field. Further, a potential of mean force study was carried out to understand the behavior of hydrogen bonds in HDBP dimers. This required the determination of hydrogen bonding criteria that captures the behavior of the HDBP dimer and is reported in this work as well.
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Affiliation(s)
- Ted Yoo
- Department of Chemical Engineering and Materials Science , University of California Irvine , 916 Engineering Tower , Irvine , California 92697-2575 , United States
| | - Hung D Nguyen
- Department of Chemical Engineering and Materials Science , University of California Irvine , 916 Engineering Tower , Irvine , California 92697-2575 , United States
| | - Mikael Nilsson
- Department of Chemical Engineering and Materials Science , University of California Irvine , 916 Engineering Tower , Irvine , California 92697-2575 , United States.,Department of Chemistry , University of California Irvine , 1102 Natural Sciences 2 , Irvine , California 92697-2025 , United States
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7
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Potential connections between the interaction and extraction performance of mixed extractant systems: A short review. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2018.07.097] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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8
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Rey J, Bley M, Dufrêche JF, Gourdin S, Pellet-Rostaing S, Zemb T, Dourdain S. Thermodynamic Description of Synergy in Solvent Extraction: II Thermodynamic Balance of Driving Forces Implied in Synergistic Extraction. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:13168-13179. [PMID: 29059520 DOI: 10.1021/acs.langmuir.7b02068] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In the second part of this study, we analyze the free energy of transfer in the case of synergistic solvent extraction. This free energy of the transfer of an ion in dynamic equilibrium between two coexisting phases is decomposed into four driving forces combining long-range interactions with the classical complexation free energy associated with the nearest neighbors. We demonstrate how the organometallic complexation is counterbalanced by the cost in free energy related to structural change on the colloidal scale in the solvent phase. These molecular forces of synergistic extraction are driven not only by the entropic term associated with the tight packing of electrolytes in the solvent and by the free energy cost of coextracting water toward the hydrophilic core of the reverse aggregates present but also by the entropic costs in the formation of the reverse aggregate and by the interfacial bending energy of the extractant molecules packed around the extracted species. Considering the sum of the terms, we can rationalize the synergy observed, which cannot be explained by classical extraction modeling. We show an industrial synergistic mixture combining an amide and a phosphate complexing site, where the most efficient/selective mixture is observed for a minimal bending energy and maximal complexation energy.
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Affiliation(s)
- J Rey
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule , Bat. 426, 30207 Bagnols sur Cèze, France
| | - M Bley
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule , Bat. 426, 30207 Bagnols sur Cèze, France
| | - J-F Dufrêche
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule , Bat. 426, 30207 Bagnols sur Cèze, France
| | - S Gourdin
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule , Bat. 426, 30207 Bagnols sur Cèze, France
| | - S Pellet-Rostaing
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule , Bat. 426, 30207 Bagnols sur Cèze, France
| | - T Zemb
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule , Bat. 426, 30207 Bagnols sur Cèze, France
| | - S Dourdain
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule , Bat. 426, 30207 Bagnols sur Cèze, France
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9
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Braatz AD, Antonio MR, Nilsson M. Structural study of complexes formed by acidic and neutral organophosphorus reagents. Dalton Trans 2017; 46:1194-1206. [DOI: 10.1039/c6dt04305d] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The coordination of the trivalent 4f ions, Ln = La3+, Dy3+, and Lu3+, with neutral and acidic organophosphorus reagents, both individually and combined, was studied by use of X-ray absorption spectroscopy.
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Affiliation(s)
- Alexander D. Braatz
- Department of Chemical Engineering and Materials Science
- University of California Irvine
- Irvine
- USA
- Nuclear Security and Isotope Technology Division
| | - Mark R. Antonio
- Chemical Sciences & Engineering Division
- Argonne National Laboratory
- Lemont
- USA
| | - Mikael Nilsson
- Department of Chemical Engineering and Materials Science
- University of California Irvine
- Irvine
- USA
- Department of Chemistry
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Antonio MR, Ellis RJ, Estes SL, Bera MK. Structural insights into the multinuclear speciation of tetravalent cerium in the tri-n-butyl phosphate–n-dodecane solvent extraction system. Phys Chem Chem Phys 2017; 19:21304-21316. [DOI: 10.1039/c7cp03350h] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Macroscopic phase behaviors in the liquid–liquid extraction are explained by microscopic, reverse micellar fluid structures containing tetranuclear Ce(iv) clusters revealed by use of X-ray spectroscopy and scattering of the light and dense organic phases.
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Affiliation(s)
- Mark R. Antonio
- Chemical Sciences and Engineering Division
- Argonne National Laboratory
- Argonne
- USA
| | - Ross J. Ellis
- Chemical Sciences and Engineering Division
- Argonne National Laboratory
- Argonne
- USA
| | - Shanna L. Estes
- Chemical Sciences and Engineering Division
- Argonne National Laboratory
- Argonne
- USA
| | - Mrinal K. Bera
- Chemical Sciences and Engineering Division
- Argonne National Laboratory
- Argonne
- USA
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Rey J, Dourdain S, Dufrêche JF, Berthon L, Muller JM, Pellet-Rostaing S, Zemb T. Thermodynamic Description of Synergy in Solvent Extraction: I. Enthalpy of Mixing at the Origin of Synergistic Aggregation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:13095-13105. [PMID: 27951687 DOI: 10.1021/acs.langmuir.6b02343] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Revisiting aggregation of extractant molecules into water-poor mixed reverse micelles, we propose in this paper to identify the thermodynamic origins of synergy in solvent extraction. Considering that synergistic extraction properties of a mixture of extractants is related to synergistic aggregation of this mixture, we identify here the elements at the origin of synergy by independently investigating the effect of water, acid, and extracted cations. Thermodynamic equations are proposed to describe synergistic aggregation in the peculiar case of synergistic solvent extraction by evaluating critical aggregation concentration (CAC) as well as specific interactions between extractants due to the presence of water, acid and cations. Distribution of two extractant molecules in the free extractants and in reverse micelles was assessed, leading to an estimation of the in-plane interaction parameter between extractants in the aggregates as introduced by Bergström and Eriksson ( Bergström, M.; Eriksson, J. C. A Theoretical Analysis of Synergistic Effects in Mixed Surfactant Systems . Langmuir 2000 , 16 , 7173 - 7181 ). Based on this model, we study the N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA) and di(2-ethylexyl) phosphoric acid (HDEHP) mixture and show that adding nitric acid enhances synergistic aggregation at the equimolar ratio of the two extractants and that this configuration can be related to a favored enthalpy of mixing.
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Affiliation(s)
- J Rey
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
| | - S Dourdain
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
| | - J-F Dufrêche
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
| | - L Berthon
- RadioChemistry & Processes Department, Nuclear Energy Division, CEA , 30207 Bagnols sur Cèze, France
| | - J M Muller
- RadioChemistry & Processes Department, Nuclear Energy Division, CEA , 30207 Bagnols sur Cèze, France
| | - S Pellet-Rostaing
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
| | - T Zemb
- ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
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Rey J, Dourdain S, Berthon L, Jestin J, Pellet-Rostaing S, Zemb T. Synergy in Extraction System Chemistry: Combining Configurational Entropy, Film Bending, and Perturbation of Complexation. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:7006-7015. [PMID: 26053416 DOI: 10.1021/acs.langmuir.5b01478] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Iron-uranium selectivity in liquid-liquid extraction depends not only on the mole fraction of extractants, but also on the nature of the diluent used, even if the diluent has no complexation interaction with the extracted ions. Modeling strong nonlinearity is difficult to parametrize without a large number of parameters, interpreted as "apparent constants". We determine in this paper the synergy curve versus mole fraction of HDEHP-TOPO (di(2-ethylexyl) phosphoric acid/tri-n-octyl phosphine oxide) and compare the free energy of aggregation to the free energy of extraction in various diluents. There is always a concomitant maximum of the two quantities, but with a gradual influence on intensity. The diluent is wetting the chains of the reverse aggregates responsible of the extraction. We show here that the intensity of the unexplained synergy peak is strongly dependent on the "penetrating" or "nonpenetrating" nature of the diluent. This experimental determination allows us to attribute the synergy to a combination of entropic effects favoring extraction, opposed to perturbation of the first coordination sphere by penetration as well as surfactant film bending energy.
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Affiliation(s)
- J Rey
- †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
| | - S Dourdain
- †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
| | | | - J Jestin
- §Laboratoire Léon Brillouin CEA/CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France
| | - S Pellet-Rostaing
- †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
| | - T Zemb
- †ICSM/LTSM, CEA/CNRS/UM2/ENSCM UMR5257, Site de Marcoule, Bat. 426, 30207 Bagnols sur Cèze, France
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Braatz A, Nilsson M. Fluorescence studies of metal complexes in synergistic extraction systems combining dibutyl phosphoric acid and tri-n-butyl phosphate. J Radioanal Nucl Chem 2014. [DOI: 10.1007/s10967-014-3487-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Ellis RJ, Anderson TL, Antonio MR, Braatz A, Nilsson M. A SAXS study of aggregation in the synergistic TBP-HDBP solvent extraction system. J Phys Chem B 2013; 117:5916-24. [PMID: 23647100 DOI: 10.1021/jp401025e] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The macroscopic phase behaviors of a solvent system containing two extractants, tri-n-butyl phosphate (TBP) and di-n-butyl phosphoric acid (HDBP) in n-dodecane, were investigated through use of liquid-liquid extraction and small-angle X-ray scattering (SAXS) experiments. Five organic solutions, each containing a total extractant concentration (TBP + HDBP) of 1 M in varying molar ratios (0, 0.25, 0.5, 0.75, and 1.0 [TBP]:[TBP + HDBP]), were contacted with 0.2 M HNO3 aqueous solutions without and with dysprosium(III) at a concentration of 10(-4) M. An enhancement of the extraction of Dy(3+)--due to effects of synergism arising from the binary combination of extractants--was observed. SAXS data were collected for all solution compositions from 0 to 1 mol-fraction end ratios of TBP after contact with the acidic aqueous solutions both in the absence and presence of Dy as well as for the organic phases before aqueous contact. In the precontacted solutions, no notable changes in the SAXS data were observed upon combining the extractants so that the scattering intensity (I) measured at zero angle (Q = 0 Å(-1))--parameter I(0)--the experimental radius of gyration (R(g)), and the maximum linear extent (MLE) of the extractant aggregates were arithmetic averages of the two end members, 1 M HDBP, on the one hand, and 1 M TBP, on the other. In contrast, after contact with the aqueous phases with and without Dy(3+), a significant reorganization occurs with larger aggregates apparent in the extractant mixtures and smaller in the two end member solutions. In particular, the maximum values of the metrical parameters (I(0), R(g), and MLE) correlate with the apparent optimal synergistic extraction mole ratio of 0.25. The SAXS data were further analyzed using the recently developed generalized indirect Fourier transformation (GIFT) method to provide pair-distance distribution functions with real-space information on aggregate morphology. Before aqueous contact, the organic phases show a systematically varying response from globular-like reverse micelles in the case of 1 M TBP to rod-shaped architectures in the case of 1 M HDBP. After aqueous contact, the aggregate morphologies of the mixed extractant systems are not simple linear combinations of those for the two end members. Rather, they have larger and more elongated structures, showing sharp discontinuities in the metrics of the aggregate entities that are coincident with the synergistic extraction mixture for Dy(3+). The results in this initial study suggest a supramolecular, micellization aspect to synergism that remains underexplored and warrants further investigation, especially as it concerns the contemporary relevance to decades-old process chemistry and practices for high throughput separations systems.
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Affiliation(s)
- Ross J Ellis
- Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439-4831, USA.
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