Synergistic Extraction of Trivalent Actinides by Mixtures of Thenoyltrifluoroacetone and Neutral Oxo Donors

Abstract

The synergistic extraction of trivalent actinides Am, Cm, Bk, and Cf has been studied by mixtures of HTTA and TOPO as well as DOSO in xylene at 30°C. HTTA-S (TOPO, DOSO) interaction corrections have been applied to calculate the “free” S concentrations in the organic phase. In the extraction of trivalent actinides, the third-power dependence on [HTTA]_org at a fixed [S]_org has been observed only after applying this correction. The synergistic species M(TTA)₃.S and M(TTA)₃.2S were found to be extracted into the organic phase whose stability constants (β₁, β₂, and K ₂) have been evaluated. Extraction by HTTA + S(S = TOPO, DOSO, TBP, TBTP) shows the order of extraction to be Tm > Cf > Bk > Eu > Pm > Am > Cm for the trivalent ions. The Am/Cm separation factor with the synergistic mixtures is ～3 whereas with HTTA alone it is ～6 when they are extracted from the chloroacetate buffer.     

Solvent Extraction Separation of Some Actinides and Lanthanides with 2-Thenoyltifluoroacetone

Abstract

Solvent extraction behavior of Th(IV) and U(VI) and some lanthanides [Ce(III), Nd(III), Eu(III), Tb(III), and Yb(III)] from thiocyanate medium into sulfoxides and/or 2-thenoyltrifluoroacetone has been studied. The actinides are found to be favorably extracted by both the extractants. The alkyl sulfoxides extract Th(IV) and U(VI) as Th(SCN)₄·3DPSO, Th(SCN)₄·3DOSO, UO₂ (SCN)₂·2DPSO, and UO₂(SCN)₂·3DOSO. The chelate extracts the metals in the following order: U(VI) < Th(IV) < Eu(IV) < Tb(III) < Tb(III) < Ce (III) or Nd(III).     

Extraction of some Hexavalent Actinide Ions from Nitric Acid Medium using Several Substituted Diglycolamides

Several substituted diglycolamides, namely TPDGA, THDGA, TODGA, and TDDGA, were evaluated in a comparative study on the extraction of hexavalent actinide ions such as UO₂²⁺, NpO₂²⁺, and PuO₂²⁺ from nitric acid medium. The acid extraction constants (K_H) for the diglycolamides were determined to be 3.8 ± 0.6, 1.6 ± 0.1, 4.1 ± 0.4, and 1.4 ± 0.2 for TPDGA, THDGA, TODGA, and TDDGA, respectively. Though metal ion extraction generally increased with increasing the feed acid concentration, the nature of the extracted species changed with aqueous-phase acidity. While complexes of the type MO₂(NO₃)₂·nL (where L is the diglycolamide extractant and n is 1 and 2) were found to be extracted at 1 M HNO₃, the average number of ligand molecules associated with the complex decreased to ?1 when the nitric acid concentration increased to 3 M. These results have great significance from the actinide separation point of view, as the actinides ions can be made virtually inextractable by adjusting their oxidation state. The thermodynamic parameters were also calculated, which indicated spontaneous reactions with large exothermicities.     

Extraction of Uranium and Thorium from Nitric Acid Solution by TODGA in Ionic Liquids

Extraction of uranium (UO₂²⁺) and thorium (Th⁴⁺) from a nitric acid solution into an imidazolium-type ionic liquids (ILs) of 1-alkyl-3-methylimidazolium hexafluorophosphate ([C_nmim][PF₆], n = 6 or 8) was carried out using N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) as an extractant. It was found that the extraction efficiencies of UO₂²⁺ and Th⁴⁺ ions are higher in comparison with that done in n-dodecane. The extraction mechanism was deduced by the slope analysis and extraction experiment. Transfer of both ions is assumed to proceed predominantly through the neutral solvation mechanism from nitric acid solution into ILs. The UO₂²⁺ ion forms a 1:2 complex with TODGA in ILs at lower acidity, and a 1:1 complex in ILs and in n-dodecane at higher acidity. The Th⁴⁺ ion forms a 1:2 complex with TODGA in C₆mimPF₆ IL or a 1:1 complex in C₈mimPF₆ IL at lower acidity and a 1:1 complex in both ILs, and n-dodecane at higher acidity. Stripping studies were conducted using sodium salt of EDTA as a stripping ligand. The thermodynamics of extracting UO₂²⁺ ions and Th⁴⁺ ions from a 3 M HNO₃ solution was also studied. The results indicated that the extraction reactions are spontaneous and go through an exothermic process.     

The Influence of Extractant Structure on the Solvent Extraction of Uranium(VI) and Thorium(IV) from Nitrate Media by Dialkyl Sulphoxides

The solvent extraction of uranium(VI) and thorium(IV) from sodium nitrate solutions (0·20–6·00 M ) by a series of dialkyl sulphoxides with different structures was studied. For sulphoxides with n-alkyl groups (R₂SO, where R = n-hexyl, n-octyl and n-decyl) using 0·20 M solutions in xylene, the extractions of both uranium and thorium are relatively high, and the values of the separation factor β_Th^U are correspondingly low (≈20). Replacement of an n-hexyl group by a cyclohexyl group has little effect on metal extraction, whilst the introduction of a second cyclohexyl group causes a slight decrease in extraction. Similarly, there is little variation in the extraction of uranium and thorium through the series of asymmetrical compounds RR′SO, where R = n-octyl and R′ = cyclopentyl, cyclohexyl or cyclooctyl. When two aromatic (phenyl) rings are introduced into the sulphoxide, however, the extraction of both metals falls to zero. For the series of isomeric compounds R₂SO with C₈ alkyl groups, the separation factors increase in the order: R = n-octyl, 2-ethylhexyl, 2-octyl, 3-octyl, which is also the order of increasing steric bulk of the alkyl group. For these compounds, slope analysis studies are consistent with the formulation of the extracted metal complexes as UO₂(NO₃)₂(R₂SO)₂ and Th(NO₃)₄(R₂SO)₃. © 1997 SCI.     

Studies on the Development of a Flow-Sheet for AHWR Spent Fuel Reprocessing Using TBP

The present paper describes the results of solvent extraction studies carried out in batch mode to collect data on distribution of uranium, plutonium, and thorium using 5% TBP in n-dodecane. Extraction studies are carried out from feed solutions having bulk thorium containing aluminum and fluoride ions in ～3.00–4.00 M nitric acid at concentration levels anticipated in feed solutions during Advanced Heavy Water Reactor (AHWR) spent fuel reprocessing. Studies are carried out under varied experimental conditions. Parameters such as organic to aqueous phase ratio during extraction, concentration of nitric acid for scrubbing co-extracted thorium from loaded organic phase etc., are studied in detail. Hydroxylamine nitrate is selected for reductive stripping of plutonium in preliminary studies. Reagent mixture containing 0.30 M HAN + 0.60 M HNO₃ and 0.20 M N₂H₄ is found to be optimum for plutonium partitioning. This paper also describes the extraction and stripping of uranium and plutonium in co-current mode. The extraction behavior of relevant fission products is studied from a simulated feed solution. A preliminary study on a few commercially available reducing agents is also included. These data are useful in developing a flow-scheme for the recovery of uranium and plutonium from spent fuel originating from AHWR.     

4-ACYLBIS(1-PHENYL-3-METHYL-5-PYRAZOLONES) AS EXTRACTANTS FOR f-ELEMENTS

ABSTRACT

The liquid-liquid extraction of early actinides such as thorium(IV) and uranium(VI) and trivalent lanthanoids such as neodymium(lll), europium(lll) and lutetium(lll) from nitrate solutions was studied using 4-sebacoylbis(1-phenyl-3-methyl-5-pyrazolone) (H₂SP) and 4-dodecandioyl-bis(1-phenyl-3-methyl-5-pyrazolone) (H₂DdP) in chloroform as extractants. The results demonstrate that these metal ions are extracted into chloroform as Th(SP)₂, Th(DdP)₂, UO₂(HSP)₂, UO₂(HDdP)₂, Ln(SP)(HSP) and Ln(DdP)(HDdP) with H₂SP or H₂DdP. The equilibrium constants of the above species were deduced by non-linear regression analysis. The results clearly highlight that thorium(IV) can be selectively separated from uranium(Vl) and trivalent lanthanoids when extracted from 0.2 mol/dm³ nitric acid solutions using 4-acylbis(1-phenyl-3-methyl- 5-pyrazolones). Thorium(IV), uranium(VI) and lutetium(lll) complexes of H₂SP were synthesised and characterised by IR and ¹H NMR spectral data to further clarify the nature of the complexes.     

Extraction of uranium(VI) from nitric acid solutions using N,N-dihexyloctanamide in ionic liquids: Solvent extraction and spectroscopic studies

Liquid-liquid extraction studies of uranium(VI) were carried out from nitric acid medium using di-n-hexyloctanamide (DHOA) in several room-temperature ionic liquids (RTIL). The extraction of the metal ion as a function of nitric acid concentration showed different trends based on the alkyl substituents of the RTIL. While the D_U values decreased with increasing HNO₃ concentration (up to ca. 0.5 M) with [C₄mim][NTf₂] and [C₆mim][NTf₂], almost no change was seen with [C₈mim][NTf₂]. This suggested that while a cation-exchange mechanism is operative with the former diluents, which was to a much lower extent for the latter. The extracted species were found to contain about 2 molecules of DHOA from the feed solutions containing either 0.01 M and 4 M HNO₃, which was arrived at from the ligand-concentration-variation experiments. Recycling studies were also performed by carrying out stripping and radiolytic stability studies. The nature of the extracted species as ascertained from the UV-visible spectrophotometry studies indicated similarity between the extracts obtained in RTIL medium, which were entirely different from that observed with n-dodecane as the diluent.     

Separation and Recovery of Uranium,Neptunium, and Plutonium from High Level Waste Using Tributyl Phosphate: Countercurrent Studies with Simulated Waste Solution

ABSTRACT

The present work deals with countercurrent extraction studies on the partitioning of uranium, neptunium, and plutonium using 30% tributyl phosphate (TBP) from simulated high level waste solution generated during reprocessing of spent uranium fuel from pressurized heavy water reactors. The oxidation states of neptunium and plutonium were adjusted either by 0.01 M potassium dichromate or 0.01 M dioxovanadium ion. Neptunium and plutonium, extracted in the TBP phase, were stripped together using a mixture containing 0.05 M ascorbic acid and 0.25 M hydrogen peroxide in 2.0 M nitric acid solution. Although dioxovanadium ion is more effective for proper adjustment of the oxidation states of plutonium and neptunium, subsequent recovery of these actinides from loaded TBP is better if potassium dichromate is used for the valency adjustment. Results of the stagewise analysis of extraction and stripping of actinides using mixer-settlers are presented.     

Synergistic Extraction of U(VI), Th(IV), and Lanthanides(III) from Nitric Acid Solutions Using Mixtures of TODGA and Dinonylnaphthalene Sulfonic Acid

The extraction of U(VI), Th(IV), and lanthanides(III) from aqueous nitric acid solutions with mixtures of N,N,N′,N′-tetra(n-octyl)diglycolamide (TODGA) and dinonylnaphtalene sulfonic acid (HDNNS) in n-decane has been investigated. The extraction efficiency of U(VI), Th(IV), and Ln(III) ions is greatly enhanced by addition of HDNNS to an organic phase containing TODGA. The synergistic effect arises from the higher hydrophobicity of U(VI), Th(IV), and Ln(III) extracted species formed by TODGA and DNNS^? anions as compared to those formed by TODGA and NO₃^? ions as counter anions. The synergistic effect for U(VI), Th(IV), and Ln(III) extraction from aqueous nitric acid solutions with mixtures of TODGA and HDNNS becomes weaker when the acidity of the aqueous phase increases. A high synergistic enhancement is accompanied with a high selectivity of Ln(III) extraction from nitric acid solutions.     

The Extraction of Uranium(VI) from Mineral Acid Solutions by Di-4-octylphenylphosphoric Acid (DOPPA)

Abstract

The extraction of uranium(VI) from sulfuric, hydrochloric, nitric, and perchloric acid was studied using dioctylphenylphosphoric acid (DOPPA) in heptane as extractant. At low aqueous acid concentration, an ion-exchange mechanism was generally observed and the extracted species was of the type UO₂A₄H₂. Deviation from this behavior was observed at higher acid concentrations. From perchloric acid solutions, after an initial decrease, the extraction coefficient increased after 3 to 4 N acid. Some of the explanations offered in the literature for this behavior in the case of di-2-ethylhexylphosphoric acid (DEHPA) have been critically examined. Extraction of mineral acids, particularly HCI and HNO₃, was also observed with DOPPA but to a lesser extent than with DEHPA.     

Extraction of Uranium(VI) and Plutonium(IV) with Tetra-Alkylcarbamides

ABSTRACT

The use of tetra-alkylcarbamides as novel extractants for the separation of uranium(VI) and plutonium(IV) by solvent extraction from spent nuclear fuels is investigated in this study. Batch extraction experiments show that tetra-alkylcarbamides strongly extract U(VI) with high distribution ratios. Plutonium(IV) can be co-extracted with U(VI) at high nitric acid concentration, while high U(VI)/Pu(IV) selectivities can be reached at lower acidity. Loading capacity experiments with high uranium concentrations show that alkyl chains longer than butyl are necessary to avoid third phase formation. Nevertheless, the viscosity of uranium-loaded solvents gets too high with alkyl chains longer than pentyl. Overall, this study shows that with TPU extractant (with four pentyl chains), an efficient co-extraction of uranium and plutonium can be reached (D_U,Pu > 1) for a concentration of nitric acid higher than 4 mol?L^?1, while the partition between uranium(VI) and plutonium(IV) could be operated even at 2 mol?L^?1 nitric acid without redox chemistry.     

THE EXTRACTION BY N.N'TETRABUTYLGLUTARAMIDES II. EXTRACTION OF U(VI), Pu(IV) AND SOME FISSION PRODUCTS

The extraction of U(VI) and Pu(IV) from aqueous nitrate solutions by N,N'-tetrabutylglutaramide (TBGA) has been investigated. At low acidities, the extraction takes place via the formation of respectively UO₂(NO₃)₂. TBGA and Pu(NO₃)₄. TBGA which seem to be linked with additionnal molecules of TBGA in the second coordination sphere of the metal. When the saturation of TBGA by UO₂ ²⁺solutions is reached, the uranyl complex reorganizes to give a polymer (UO₂(NO₃)₂ TBGA)_x.

At high acidities, the anionic complexes : [UO₂(NO₃)₃, ^?] [HTBGA⁺] and probably [HPu(NO₃)₆?] [HTBGA+] are observed.     

DEVELOPMENT OF A FAST AND EFFICIENT SEPARATION FOR SHORT-LIVED PLUTONIUM ISOTOPES PRODUCED IN ACCELERATOR-BASED IRRADIATIONS

ABSTRACT

A novel, fast and simple separation procedure is presented for separation of plutonium from lighter actinides and fission products. Classical methods, such as TTA-extraction and anion exchange resin techniques, were examined but failed to provide sufficient separation from lighter actinides. A successful procedure based on solid phase extraction chromatography was developed. Plutonium was effectively separated from interfering activities within 8?minutes using TEVA-resin®, a quaternary amine-based liquid anion exchanger sorbed on an inert support. Recoveries of about 70% were achieved for plutonium with decontamination factors of 10⁵ to 10s from neptunium, uranium and thorium.     

Feasibility of Using Di-Dodecyl-Di-Octyl Diglycolamide for Partitioning of Minor Actinides from Fast Reactor High-Level Liquid Waste

The unsymmetrical diglycolamide, di-dodecyl-di-octyl diglycolamide (D³DODGA) is a modifier-free extractant proposed for partitioning of trivalent actinides from nitric acid medium. D³DODGA has been evaluated for the feasibility of using it in the absence of a phase modifier, for the partitioning of minor actinides from fast reactor high-level liquid waste (FR-HLLW). The extraction behavior of various metal ions present in the simulated FR-HLLW was studied in a solution of 0.1 M D³DODGA/n-dodecane from nitric acid medium. The distribution ratio of about 20 metal ions was measured as a function of concentration of nitric acid and other interfering ion. The extraction was found to be strongly dependent on the oxidation state of the metal ion. The extraction of Am(III) from 3–4 M nitric acid medium was quantitative in a single contact. However, it was accompanied by the quantitative extraction of fission products such as trivalent lanthanides (Ln(III)), Y(III), and Zr(IV). The extraction of Sr(II), Pd(II), and Ru(III) in 0.1 M D³DODGA/n-dodecane was not insignificant, but quite low. The extraction of Ba(II), Ni(II), Mo(VI), and Fe(III) was marginal and the extraction of Co(II), Sb(III), Mn(II), and Cs(I) in 0.1 M D³DODGA/n-dodecane was negligible. Our results indicated that 0.1 M D³DODGA/n-dodecane is a promising candidate for the separation of trivalent actinides from fast reactor high-level liquid waste containing significant quantities of trivalent lanthanides and actinides.     

Comprehensive Studies on Third Phase Formation: Application to U(VI)/Th(IV) Mixtures Extracted by TBP in N-dodecane

ABSTRACT

Phase splitting of tributylphosphate (TBP)/n-dodecane organic phases resulting from the extraction of UO₂(NO₃)₂, Th(NO₃)₄ and mixtures of both actinides from aqueous nitrate solutions has been investigated. Limiting organic concentrations (LOC) and metals distribution beyond third phase formation have been determined, with comparison between the cases of single metal-systems and metals mixtures. Simultaneous quantification of TBP and both metals was achieved through X-ray fluorescence (XRF) analyses. LOC studies reveal that thorium (IV) drives the third phase formation as it is the most destabilizing element in the solvent. After organic phase splitting, studies of the distributions of metals between the heavy organic phase (HOP) and the diluted organic phase (DOP) in the case of U^(VI)/Th^(IV) mixtures revealed that they are similar to those observed when both metals are alone in the solvent: Thorium (IV) has a strong affinity for the HOP, whereas uranium (VI) distributes both in HOP and in DOP. A supersaturation coefficient (N_LOC) is proposed as a new tool to account for the data obtained in the present study. Furthermore, the approach was successfully applied to analyse available data in the literature regarding thorium (IV) distribution studies after phase splitting in various TBP-alkane solvents. Such a study beyond third phase formation paves the way for studying the mechanism involved in third phase formation, as the metal is clearly identified as the key parameter.     

EXTRACTION STUDY FOR TRUEX PROCESS USING SHORT-LIVED RADIONUCLIDES PRODUCED BY NEUTRON IRRADIATION OF URANIUM

The extraction behavior of short-lived fission products and neptunium was studied by using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide under the conditions of the transuranic elements extraction (TRUEX) process. The short-lived fission products and neptunium were produced by neutron irradiation of UO₂ of natural uranium, and the extraction behavior of ⁹³Y, ⁹⁹Mo, ⁹⁷Zr, ¹²²Sb, ¹³²Te, ¹³³I, ¹⁴³Ce, and ²³⁹Np was simultaneously studied, where ¹²²Sb was produced by neutron irradiation of antimony metal. The extraction of fission products and Np under the conditions of the PUREX process was also studied for comparison. The extraction of nuclides in the presence of large amounts of uranium(VI), and the presence of oxalic acid was examined. The conditions and performance of the TRUEX extraction were discussed by considering the obtained results.     

Extraction behaviour of dioxouranium(VI) cation by two phosphorous-based liquid cation-exchangers in room-temperature ionic liquids

Extraction of uranium with bis-(2-ethylhexyl) phosphonic acid (PC-88A) and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex-272) was studied in several imidazolium-based room-temperature ionic liquids (RTILs), C_nmim·X (where n = 4, 6, 8 and X = PF₆ and Tf₂N). The extraction kinetics was slow and about 0.5–1 h equilibration time was required for most of the extraction systems, except in C₈mim·PF₆, where 2 h and 4 h were required to reach the equilibrium values for PC-88A and Cyanex-272, respectively. The extraction of UO₂²⁺ ion by the two ligands was significantly affected by the nature and the composition of the RTILs.     

THE EXTRACTION OF RHODIUM FROM AQUEOUS NITRIC ACID BY DINONYLNAPHTHALENE SULPHONIC ACID

The extraction of rhodium from aqueous nitric acid using dinonylnapthalene sulphonic acid has been investigated. The extraction occurs readily from 0.1M to 1.0m nitric acid and, since the rhodium is extracted as [Rh(H₂O)₆] ³⁺into the inverted micelles of the organic solution,equilibration times are less than 5 minutes. Extraction is enhanced by the addition of nitrite ion to form [Rh(H₂O)₅NO₂] ²⁺as the extracted species.     

1-Phenyl-3-methyl-4-benzoyl-pyrazolone-5: A Promising Extractant for Plutonium

Abstract

Pyrazolones and isoxazolones have been found to be promising extractants for metal ions, particularly from strong acidic media and in the presence of complexing anions. Extraction constants (log kex) in toluene medium at 25°C for PuX₄ species, where X = 1-phenyl-3-methyl-4-acetyl-pyrazolone-5 (HPMAP), 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP), or 1-phenyl-3-methyl-4-(3:5-dinitrobenzoyl)pyrazolone-5 (HPMDP), are determined as 11.35 ± 0.04, 12.89 ± 0.03, and 12.73 ± 0.02, respectively. These values are comparable to the corresponding value for 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) and several order of magnitude larger than that for 2-thenoyltrifluoroacetone (HTTA). A systematic study is carried out to investigate the extraction behavior of these β-diketones toward plutonium present in the analytical waste solution obtained during the determination of uranium in a (U, Pu) fuel sample by the Davies Gray method. Whereas 0.3 M HPMBP extracts ≥85% of the plutonium present in a single step, maximum extraction observed with other reagents is ?0.1% HTTA, 0.3% HPMAP, and 2.5% HPBI. The extraction of plutonium increases with different diluents in the order n-dodecane < n-hexane < CHCl₃ < CCl₄ < toluene. Extracted plutonium is quantitatively stripped with either 10 M HNO₃ or 1:1 HCl + 0.1 M hydroquinone.