Studies on the third-phase formation in DHDECMP/dodecane/HNO<sub>3</sub>

Lohithakshan, K. V.; Aswal, Vinod K.

doi:10.1524/ract.2011.1811

Cited by 14 publications

(12 citation statements)

References 13 publications

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“…40 Several papers on ionic-liquid-based extraction systems describe that the stoichiometry of extracted metal complexes can be different in ionic liquid diluents and in molecular diluents like n-dodecane. 14,[42][43][44] The variation of logD as a function of pH of the aqueous phase was plotted and it resulted in a straight line with the slope of 0.95 (Figure 4). This indicates that one Eu(III) ion exchanges with the H + ion of one DEHDGA molecule to form an ion-associated complex.…”

Section: Extraction Mechanismmentioning

confidence: 99%

Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

2014

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Section: Extraction Mechanismmentioning

confidence: 99%

Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

2014

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“…From there, the uranium and plutonium are recovered. At high metal loading, however, the organic phase can, itself, separate into two phases; − the heavy lower layer, which is commonly called the third phase, contains high concentrations of the metal-ion/TBP complexes and mineral acids, whereas the light upper layer, which is commonly called the light organic phase, contains lower concentrations of metal ions, TBP, and mineral acids but is rich in the organic diluent. Formation of the third phase is highly undesirable because it causes failure of the extraction process and because the concentrations of uranium and plutonium in the third phase can be high enough to risk an uncontrolled nuclear chain reaction.…”

Section: Introductionmentioning

confidence: 99%

“…In the past few decades, extensive experiments have been carried out to delineate the conditions under which the third phase forms and to investigate the microscopic structures of the coexisting third and light organic phases. − Nuclear magnetic resonance (NMR), , extended X-ray absorption fine structure, and infrared spectroscopies have been used to gain information about the molecular structures on the atomic length scale, and small-angle X-ray and neutron scattering (SAXS and SANS) measurements have been made to characterize the larger structures at the nanometer length scale. − The metal/TBP complexes were first proposed by Chiarizia and co-workers, on the basis of SANS profiles, to form reverse micelles. − However, in general, a SANS or indeed a SAXS profile can be reproduced by a few different structural models, and hence, considerable care is required to correctly interpret such profiles with unique structures . Nevertheless, note that extraction processes other than PUREX also exhibit the formation of the third phase and the coexistence of this phase with the organic phase, and reverse micelles have been suggested to play a key role in such cases. , …”

Section: Introductionmentioning

confidence: 99%

A Novel Microemulsion Phase Transition: Toward the Elucidation of Third-Phase Formation in Spent Nuclear Fuel Reprocessing

Motokawa

Akutsu

et al. 2018

J. Phys. Chem. B

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We present evidence that the transition between organic and third phases, which can be observed in the plutonium uranium reduction extraction (PUREX) process at high metal loading, is an unusual transition between two isotropic bicontinuous microemulsion phases. As this system contains so many components, however, we have been seeking first to investigate the properties of a simpler system, namely, the related metal-free, quaternary water/n-dodecane/nitric acid/tributyl phosphate (TBP) system. This quaternary system has been shown to exhibit, under appropriate conditions, three coexisting phases: a light organic phase, an aqueous phase, and the so-called third phase. In the current work, we focused on the coexistence of the light organic phase with the third phase. Using Gibbs ensemble Monte Carlo (GEMC) simulations, we found coexistence of a phase rich in nitric acid and dilute in n-dodecane (the third phase) with a phase more dilute in nitric acid but rich in n-dodecane (the light organic phase). The compositions and densities of these two coexisting phases determined using the simulations were in good agreement with those determined experimentally. Because such systems are generally dense and the molecules involved are not simple, the particle exchange rate in their GEMC simulations can be rather low. To test whether a system having a composition between those of the observed third and organic phases is indeed unstable with respect to phase separation, we used the Bennett acceptance ratio method to calculate the Gibbs energies of the homogeneous phase and the weighted average of the two coexisting phases, where the compositions of these phases were taken both from experimental results and from the results of the GEMC simulations. Both demixed states were determined to have statistically significant lower Gibbs energies than the uniform, mixed phase, providing confirmation that the GEMC simulations correctly predicted the phase separation. Snapshots from the simulations and a cluster analysis of the organic and third phases revealed structures akin to bicontinuous microemulsion phases, with the polar species residing within a mesh and with the surface of the mesh formed by amphiphilic TBP molecules. The nonpolar n-dodecane molecules were observed in these snapshots to be outside this mesh. The only large-scale structural differences observed between the two phases were the dimensions of the mesh. Evidence for the correctness of these structures was provided by the results of small-angle X-ray scattering (SAXS) studies, where the profiles obtained for both the organic and third phases agreed well with those calculated from simulations. Finally, we looked at the microscopic structures of the two phases. In the organic phase, the basic motif was observed to be one nitric acid molecule hydrogen-bonded to a TBP molecule. In the third phase, the most common structure was that of the hydrogen-bonded TBP-HNO-HNO chain. A cluster analysis provided evidence for TBP forming an extended, connected network in both phases. S...

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“…Crown ethers (CE) have attracted great attention due to their potential for use as solvent extraction ligands in reprocessing of radioactive wastes [1][2][3][4][5]. Since the 1990s, the dicyclohexano-substituted crown ethers, namely dicyclohexano-18-crown-6 (DCH18C6) and its tertbutyl substituted derivatives, are considered as promising compounds for strontium separation from radioactive liquid wastes [6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

γ-radiation effect on dicyclohexano-18-crown-6 aqueous solution in the presence of metal cations

Yu¹,

Peng²,

Li³

et al. 2014

Radiochimica Acta

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radiation effect on dicyclohexano-18-crown-6 aqueous solution in the presence of metal cations Abstract: -radiation effect on dicyclohexano-18-crown-6 (DCH18C6) aqueous solution in the presence of metal cations, such as K + and Sr 2+ , was investigated, and some pale yellow precipitates were obtained at doses above 100 kGy. It was found that the complexation interaction of metal cations could accelerate the conversion of DCH18C6 into oligomers and the formation of precipitates, but it did not affect the formation mechanism of precipitates. Furthermore, the salting-out effect of metal cations played an important role in the precipitation. In order to inhibit the radiation-induced precipitation of DCH18C6 in water phase, nitric acid with a concentration of more than 1 M could be added to the system. The methods and results for analyzing radiation-induced products reported in this work are useful to understand the radiation chemistry behavior of DCH18C6 which is used as the extractant in the separation of long half-life radionuclides from spent nuclear fuel.

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Studies on the third-phase formation in DHDECMP/dodecane/HNO₃

Cited by 14 publications

References 13 publications

Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

A Novel Microemulsion Phase Transition: Toward the Elucidation of Third-Phase Formation in Spent Nuclear Fuel Reprocessing

γ-radiation effect on dicyclohexano-18-crown-6 aqueous solution in the presence of metal cations

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Studies on the third-phase formation in DHDECMP/dodecane/HNO3

Cited by 14 publications

References 13 publications

Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

Solvent extraction of europium(iii) to a fluorine-free ionic liquid phase with a diglycolamic acid extractant

A Novel Microemulsion Phase Transition: Toward the Elucidation of Third-Phase Formation in Spent Nuclear Fuel Reprocessing

γ-radiation effect on dicyclohexano-18-crown-6 aqueous solution in the presence of metal cations

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Studies on the third-phase formation in DHDECMP/dodecane/HNO₃