Pu Extraction Research Articles

Unique Selectivity Reversal in the Complexation of Uranium(VI) and Plutonium(IV) with Two Novel C-Pivoted Tripodal Amide Ligands: Extraction and Liquid Membrane Transport Studies

ABSTRACT Two new carbon pivoted tripodal amide-containing ligands with different spacers (L I : -CH2- spacer; L II : -CH2-CH2- spacer) have been investigated for the liquid–liquid extraction of tetravalent plutonium and hexavalent uranium from nitric acid feed solutions. The studies were carried out using the ligand solutions prepared in 95% n-dodecane + 5% isodecanol. Pu(IV) extraction was higher than that of U(VI) at 3 M HNO3 for ligand L I which was just the opposite for ligand L II . Increase of the nitric acid concentration resulted in increasing extraction of both metal ions. Isodecanol variation studies exhibited decrease in the extraction of Pu(IV) and U(VI) with increasing isodecanol content in the organic phase. Greater that 98% stripping of Pu(IV) and U(VI) was obtained from the complexes of L I and L II using 0.5 M HNO3 + 0.1 M HEDTA and 1 M Na2CO3, respectively. The slope analysis study suggested the formation of 1:2 (ML2) species with Pu(IV) as well as U(VI) with both ligands at 3 M HNO3. Temperature variation studies showed that the extraction of U(VI) and Pu(IV) with both ligands is exothermic in nature. Supported liquid membrane transport experiments using 0.11 M ligands (L I and L II ) in 95% n-dodecane + 5% isodecanol indicated poor transport (<10% after 2 h) of U(VI) and Pu(IV).

Highly selective separation of tetravalent plutonium from complex system with novel phenylpyridine diamide ligands.

In this study, three phenylpyridine diamide ligands, namely, 2,2'-((pyridine-2,6-diylbis(3,1-phenylene))bis(oxy))bis(N,N-diethylacetamide) (PPEA, L1), 2,2'-((pyridine-2,6-diylbis(3,1-phenylene))bis(oxy))bis(N-ethyl-N-phenylacetamide) (PEPA, L2), and 2,2'-(((4-phenylpyridine-2,6-diyl)bis(3,1-phenylene))bis(oxy))bis(N,N-dioctylacetamide) (PPOA, L3), were synthesized and explored for the solvent extraction of Pu(iv) in a HNO3 medium using 1-(trifluoromethyl)-3-nitrobenzene as the diluent. The effects of HNO3 concentration, extractant concentration, and temperature on the Pu(iv) extraction efficiency were studied. All three extractants displayed high selectivity for Pu(iv) over other metals such as U(vi), Np(v), Am(iii), and various fission elements. At 3 M HNO3, the distribution ratio for Pu(iv) reached 27.18, in contrast to 1.11, 0.3, and 0.03 for U(vi), Np(v), Am(iii), respectively. Slope analysis and UV titration revealed the formation of 1 : 1 Pu(NO3)4/ligand complexes during extraction. The extraction reactions had negative Gibbs free energies, indicating the spontaneous nature of Pu(iv) extraction at room temperature. Furthermore, the extractants demonstrated good stripping ability and reusability, and their radiolytic stability was reasonable up to an absorbed dose of 100 kGy, underscoring their potential for practical applications. Overall, this study broadens our understanding of actinide-diamide ligand coordination and actinide chemistry during coordination, paving the way for the design and synthesis of new extractants.

Stereo‐ and Regiochemical Effect of N,N‐Dialkylamide Extractants on the Speciation of Pu Complexes

AbstractThe relationship between extractant stereochemistry and their extraction performance has only poorly been established. In order to address a part of this concern, we investigated the Pu(IV) liquid‐liquid extraction (LLE) by using the N,N‐di‐(2‐ethylhexyl)butyramide (DEHBA), as well as those of its position isomers. DEHBA (ββ‐isomer) and N‐(2‐ethylhexyl)‐N‐(oct‐3‐yl)butyramide (EHOBA or αβ‐isomer) were synthesized as a mixture of stereoisomer or stereoenriched (R,S)‐ and (S,S)‐diastereoisomers, and were all assessed for PuIV LLE. The results showed that both the position and the stereoisomerism of the aliphatic substituents affect PuIV complexation and extraction. We found that Pu extraction is lowered by factor 2 to 4 when the ethyl branching group is closer to the complexing site. UV‐vis spectroscopy showed that this extraction decrease was affected by steric hindrance inducing a deprivation of Pu inner sphere complex. Effect of stereoisomerism is highlighted for branching closer to the complexing site (α‐position). Enantiopure DEHBA stereoisomers provided similar Pu extraction, whereas a slight decrease could be noticed for the more cluttered stereoenriched (αβ)‐isomers, which was also concomitant with a smaller population of inner sphere complex. In contrast, the stereoisomers mixture led to a strong decrease of Pu extraction because of an antagonistic association in the mixed complexes.

Efficiency of dihydroxamic and trihydroxamic siderochelates to extract uranium and plutonium from contaminated soils

Actinide-based mineral phases occurring in contaminated soils can be solubilized by organic chelators excreted by plants, such as citrate. Herein, the efficiency of citrate towards U and Pu extraction is compared to that of siderophores, whose primary function is the acquisition of iron(III) as an essential nutrient and growth factor for many soil microorganisms. To that end, we selected desferrioxamine B (DFB) as an emblematic bacterial trishydroxamic siderophore and a synthetic analog, abbreviated (LCy,Pr)H2, of the tetradentate rhodotorulic acid (RA) produced by yeasts. Firstly, the uranyl speciation with both ligands was assessed in the pH range 2–11 by potentiometry and visible absorption spectrophotometry. Equilibrium constants and absorption spectra for three [UO2(DFB)Hh](h−1)+ (h = 1–3) and five [UO2(LCy,Pr)lHh](2+h−2l)+ (−1 ≤ h ≤ 1 for l = 1 and h = 0–1 for l = 2) solution complexes were determined at 25.0 °C and I = 0.1 M KNO3. Similar studies for the Fe3+/(LCy,Pr)2– system revealed the formation of five species having [Fe(LCy,Pr)]+, [Fe(LCy,Pr)OH], [Fe(LCy,Pr)(OH)2]–, [Fe(LCy,Pr)2H], and [Fe2(LCy,Pr)3] compositions. Then, the ability of DFB, (LCy,Pr)H2, and citrate to solubilize either U or Pu from pitchblende-rich soils (soils 1 and 2) or freshly plutonium-contaminated soils (LBS and PG) was evaluated by performing batch extraction tests. U was extracted significantly only by citrate after a day. After one week, the amount of U complexed by citrate only slightly exceeded that measured for the siderochelates, following the order citrate > (LCy,Pr)H2 ≥ DFB ≈ H2O, and were comparatively very low. Pu was also more efficiently extracted by citrate than by DFB after a day, but only by a factor of ~2–3 for the PG soil, while the Pu concentration in the supernatant after one week was approximately the same for both natural chelators. It remained nearly constant for DFB between the 1st and 7th day, but drastically decreased in the case of citrate, suggesting chemical decomposition in the latter case. For the Fe-rich soils 1 and 2, the efficiencies of the three chelators to solubilize Fe after a day were of the same order of magnitude, decreasing in the order DFB > citrate > (LCy,Pr)H2. However, after a week DFB had extracted ~1.5 times more Fe, whereas the amount extracted by the other chelators stayed constant. For the less Fe-rich LBS and PG soils contaminated by Pu, the amounts of extracted Fe were higher, especially after 7 days, and the DFB outperformed citrate by a factor of nearly 3. The higher capacity of the hexadentate DFB to extract Pu in the presence of Fe and its lower ability to mobilize U qualitatively agree with the respective complexation constant ratios, keeping in mind that both Pu-containing soils had a lower iron loading. Noticeably, (LCy,Pr)H2 has roughly the same capacity as DFB to solubilize U, but it mobilizes less Fe than the hexadentate siderophore. Similarly, citrate has the highest capacity to extract Pu, but the lowest to extract Fe. Therefore, compared to DFB, (LCy,Pr)H2 shows a better U/Fe extraction selectivity and citrate shows a better Pu/Fe selectivity.

Thermodynamic modeling of Pu(IV) and nitric acid extraction by 1.1 M tri-iso-amyl phosphate in n-dodecane

A thermodynamic model for the liquid–liquid extraction of tetravalent plutonium (Pu(IV)) by 1.1 M Tri iso Amyl Phosphate (TiAP) in n-dodecane was developed. The activity coefficients of species in the aqueous phase were estimated using eUNIQUAC activity coefficient model. The plutonium speciation in the aqueous nitric acid solution of 1–6 M concentration region was modelled by taking account of mono nitrate (Pu(NO3)3+), di nitrate $$({\text{Pu}}({\text{NO}}_{3} )_{2}^{2 + } )$$ , tetra nitrate (Pu(NO3)4) and hexa nitrate $$({\text{Pu}}({\text{NO}}_{3} )_{6}^{2 - } )$$ complexes. The eUNIQUAC activity coefficient model parameter and stability constant of tetra and hexa nitrate complexes were determined using the experimental water activity as well as extraction data. The distribution coefficient of nitric acid and Pu(IV) in the 1.1 M TiAP was estimated by accounting HNO3·TiAP, HNO3·2TiAP and Pu(NO3)4·2TiAP complexes in the organic phase. A good correlation between the estimated and experimental organic phase concentration of nitric acid and plutonium nitrate was obtained.

Coordination Structures of Uranium(VI) and Plutonium(IV) in Organic Solutions with Amide Derivatives.

Carbamide and monoamide derivatives are very promising molecules to achieve U(VI) and Pu(IV) extraction and separation from spent nuclear fuels through solvent extraction. Herein, coordination structures of U(VI) and Pu(IV) complexes with carbamide derivatives were characterized using X-ray crystallography as well as infrared, UV-visible, and EXAFS spectroscopies. Coordination structures are compared to those obtained for monoamide derivatives in order to better understand the role of coordination chemistry in extraction properties. Single crystals were first synthesized with a short alkyl chain carbamide analog. Carbamide complexation in the solid state is found analogous to that in the monoamide. In organic solution, upon solvent extraction from nitric acid aqueous solution, it is shown that both amide derivatives can bind in the inner and outer coordination spheres of uranium(VI) and plutonium(IV). The amount of outer sphere coordination complexes increases with the amount of nitric acid. With uranium(VI), at a nitric acid concentration up to 5 mol·L-1, amide derivatives operate predominantly in the inner coordination sphere. In contrast, Pu(IV) coordination geometry is much more sensitive toward acid concentration or ligand structure than U(VI). Pu(IV) changes from inner sphere complexation at 0.5 mol·L-1 HNO3 to mostly outer sphere complexation at 4 mol·L-1. The proportion of outer-sphere complexes is strongly influenced by the ligand structure. Higher Pu(IV) extraction is found to be correlated with the amount of Pu(IV) outer sphere species. Secondary interactions in the outer sphere coordination shell appear to be of primary importance for plutonium extraction.

Unified Framework for Modeling Reactive Extraction of Metals: Illustration on Plutonium(IV) Extraction with Tri-n-butyl Phosphate

Reactive extraction of nuclear elements from aqueous nitric acid solutions using an organic solvent is an important process operation. A thermodynamic model to predict the equilibrium compositions of the two phases will be useful in optimizing the performance of such processes. A general framework is presented in this work for modeling such systems by dividing the complex reactive metal extraction system into appropriate subsystems, whose models are combined to derive the overall model. This approach reduced the number of parameters to be estimated at each stage, making the framework reliable and accurate. The procedure is illustrated for extraction of plutonium (Pu4+) using tri-n-butyl phosphate (TBP) as the organic solvent. This model for Pu extraction correctly accounts for free TBP, the dissociation of nitric acid in concentrated solutions, and formation of hydrolyzed species of plutonium to predict the distribution coefficient of Pu(IV) accurately over the practical range of nitric acid concentration...

Electrochemical Behavior of Plutonium in Molten Fluoride Medium

A pyrochemical process for slag recycling containing trapped actinide particles into a CaF2-CaO matrix is currently in progress. Since the process requires to melt the slag (melting point above 1300°C), an additional amount of CaCl2 must be used to decrease the operating temperature below 1000°C. Then, a reducing agent (calcium) is added into the molten medium to remove the actinides in a stable metallic form after decantation. The clean salt product meets the radiological requirements to be discarded to the dedicated way (ANDRA). However, the extraction process is operated in a molten chloro-fluoride salt which is complex and quite unknown. Pu investigation in simplified media, chloride and fluoride, must lead to understand the mechanism of Pu reduction in chloro-fluoride media. Pu behavior has already been investigated in molten chloride media via electrochemical techniques by J. Serp et al. [1], O. Shirai et al. [2] and Lambertin et al. [3]. Nevertheless, data regarding this actinide behavior in molten fluoride media are incomplete [4]. Consequently, a detailed electrochemical study was carried out on plutonium in fluoride salt. The selected solvent is a mixture of two well-known salts, LiF and CaF2, melted in a crucible made of vitreous carbon in an oxygen free atmosphere (argon). Plutonium ions were introduced into the melt in the form of PuF4 powder. The setup consisted of a three electrodes assembly: tungsten as working electrode, vitreous carbon as auxiliary electrode and the potentials were referred to a platinum electrode. Cyclic voltammetry, square wave voltammetry and chronopotentiometry were coupled with thermodynamic calculations (potential-oxoacidity diagram) to investigate the electrochemical system. The acquired data will be used for a better understanding of Pu extraction from the melt. [1] J. Serp, R.J.M. Konings, R. Malmbeck, J. Rebizant, C. Scheppler, J.-P. Glatz, Electrochemical behaviour of plutonium ion in LiCl-KCl eutectic melts, J. Electroanal. Chem., 561 (2004) 143. [2] O. Shirai, T. Iwai, Y. Suzuki, Y. Sakamura, H. Tanaka, Electrochemical behavior of actinide ions in LiCl-KCl eutectic melts, J. Alloys Compd., 271-273 (1998) 685. [3] D. Lambertin, S. Ched’homme, G. Bourgès, S. Sanchez, G. Picard, Plutonium chemical properties in NaCl-KCl and CaCl2 at 1073 K, J. Nucl. Mater., 341 (2005) 124. [4] C. Hamel, Séparation actinides-lanthanides (neodyme) par extraction électrolytique en milieux fluorures fondus, vol. 3, 2005. Thesis, Toulouse.

Selective pertraction of plutonium(IV) from acidic feeds across PTFE flat sheets containing diamides with a tri-aryl-pyridine (TAP) Centre

Diamide ligands with a tri-aryl-pyridine (TAP) bridge were reported to be selective for Pu(IV) extraction in a previous study. In order to maximize the efficiency and to minimize the ligand inventory, supported liquid membrane (SLM) transport studies were carried out using N,N-di-n-octyl-TAP-diamide (LI) and N,N-dioctyl-PDAP-diamide (LII) in a diluent mixture consisting of 5% iso-decanol + 95% n-dodecane. The transport was found to be ca. 90% with LI in about 5 h which was higher than the transport rate seen with LII. Efficient mass transfer rates were seen when a mixture containing 0.5 M NH2OH + 1 M HNO3 was used in the receiver phase. Excellent selectivity for Pu was seen when the transport studies were carried out using a feed solution containing a mixture of radionuclides viz. Pu, 241Am, 233U, 152,154Eu, 137Cs and 85,89Sr in 3 M HNO3. The stability of the SLM was studied over a period 10 days while using the same SLM but with fresh feed and receiver solutions for each run.

Separation of neptunium from actinides by monoamides: a solvent extraction study

Abstract Separation of neptunium from a mixture of actinides viz. uranium, neptunium and plutonium was evaluated using two monoamides, viz. N,N,-dihexyl octanamide (DHOA) and N,N,-dihexyl decanamide (DHDA). The extraction of actinides with these ligands followed the order: U(VI)&gt;Np(IV)&gt;&gt;Pu(III). Poor extraction of Pu(III) with both the amides (DHOA and DHDA) was exploited for the mutual separation of U, Pu and Np. At 3 M HNO3, DHDA was a better extractant for all the three metal ions while Pu(III) extraction was one order magnitude lower with DHOA as compared to that seen with DHDA. Consequently, better separation factor of U(VI)/Np(IV) over Pu(III) was obtained with DHOA. In the actinide mixed solution, Pu was reduced to its +3 state followed by selective extraction of U(VI) and Np(IV). Subsequently, the mutual separation of U(VI) and Np(IV) was carried out by selective complexation and stripping of Np(IV) by acetohydroxamic acid (AHA) at 2 M HNO3, where U(VI) remained in the organic phase. The purity of the separated actinides was confirmed by alpha spectrometry. A separation scheme for the separation of Np from radioactive waste/high level waste has been proposed.

Feasibility studies of using N,N-dihexyloctanamide (DHOA) for fast reactor fuel reprocessing applications

Abstract N,N-dihexyloctanamide (DHOA) is being considered as a promising extractant in the aqueous reprocessing of spent nuclear fuels. In view of rise in temperature of the solvent during reprocessing of fast reactor fuel, the present study aimed at evaluating the physical properties such as density, viscosity, and interfacial tension and Pu(IV) extraction behavior in 1.1 M DHOA/n-dodecane as a function of temperature and duration of heating. The influence of nitric acid in altering the physical properties with respect to temperature was evaluated. Physical properties and extraction behavior of the solvent changed to a remarkable extent with temperature. Quantitative amount of Pu(IV) could be back-extracted from loaded, solvent in three contacts at 313 K. FT-IR studies were carried out to evaluate the thermal stability of the solvent. Thus, the performance of the solvent, 1.1 M DHOA/n-dodecane is satisfactory at higher temperatures also.

Influence of temperature on Pu(IV) extraction from nitric acid solutions into 30% TBP, considered within the framework of A.M. Rozen’s model and of a new (multireaction) model

Published and newly obtained data on the influence of temperature on the extraction of Pu(IV) from nitric acid solutions into 30% TBP are analyzed. The analysis shows that both A.M. Rozen’s model and the new (multireaction) model insufficiently accurately describe the influence of temperature on the Pu(IV) extraction at HNO3 concentrations in the aqueous phase of 1 M and lower, where Pu(IV) can undergo partial hydrolysis, and at HNO3 concentrations of 4 M and higher. Changes are made in the system of equilibrium constants in both models.

Used Mixed Oxide Fuel Reprocessing at RT-1 Plant

Reprocessing of the mixed uranium-plutonium spent nuclear fuel of the BN-600 reactor was performed at the RT-1 plant twice, in 2012 and 2014. In total, 8 fuel assemblies with a burn-up from 73 to 89 GW day/t and the cooling time from 17 to 21 years were reprocessed. The reprocessing included the stages of dissolution, clarification, extraction separation of U and Pu with purification from the fission products, refining of uranium and plutonium at the relevant refining cycles. Dissolution of the fuel composition of MOX UNF in nitric acid solutions in the presence of fluoride ion has occurred with the full transfer of actinides into solution. Due to the high content of Pu extraction separation of U and Pu was carried out on a nuclear-safe equipment designed for the reprocessing of highly enriched U spent nuclear fuel and Pu refining. Technological processes of extraction, separation and refining of actinides proceeded without deviations from the normal mode. The output flow of the extraction outlets in their compositions corresponded to the regulatory norms and remained at the level of the compositions of the streams resulting from the reprocessing of fuel types typical for the RT-1 plant. No increased losses of Pu into waste have been registered during the reprocessing of BN-600 MOX UNF an compare with VVER-440 uranium UNF reprocessing.

Solvent extraction of plutonium(IV) in monoamide – ammonium ionic liquid mixture

Abstract The extraction behavior of plutonium(IV) was studied in the room temperature ionic liquid, trioctylmethylammonium bis(trifluoromethanesulfonyl)imide ([N 1888 ][NTf 2 ]) containing a monoamide, N,N- dihexyloctanamide (DHOA). The unusual extraction of Pu(IV) observed in this ionic liquid system was reported in this paper. The extraction behavior of plutonium(IV) was investigated as a function of various parameters, such as feed acid concentration, extractant and ionic liquid concentration, type of the extractants, equilibration time and temperature. Changing the extractant from DHOA to tri- n -butyl phosphate reduced the distribution ratio of Pu(IV). The extraction trend of Pu(IV) in neat [N 1888 ][NTf 2 ] was compared with those observed in other ionic liquids such as 1-alkyl-3-methylimidazolium bistriflimide ([C n mim][NTf 2 ]). Pu(IV) extraction in [N 1888 ][NTf 2 ] was found to follow a combination of anion exchange mechanism and neutral solvation pathway at feed acidities above 2 M HNO 3 . The extraction of Pu(IV) in DHOA/[N 1888 ][NTf 2 ] was also compared with those observed in a molecular diluent system, DHOA/ n -DD. All thermodynamic parameters governing the extraction of plutonium(IV) in [N 1888 ][NTf 2 ] was determined and discussed in detail. Stripping of Pu(IV) from the loaded ionic liquid phase was performed using dilute nitric acid.

Effect of room temperature ionic liquid on the extraction behavior of Plutonium (IV) using a novel reagent, bis-(2-ethylhexyl) carbamoyl methoxy phenoxy-bis-(2-ethylhexyl) acetamide [Benzodioxodiamide, BenzoDODA

A novel Plutonium (Pu) (IV) selective ligand, bis-(2-ethylhexyl) carbamoyl methoxy phenoxy-bis-(2-ethylhexyl) acetamide (BenzoDODA) was studied for its Pu(IV) extraction behavior in presence of 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide {[Cnmim][Tf2N]}ionic liquids. BenzoDODA was observed to behave differently in RTIL compared to n-dodecane toward Pu(IV) extraction. The presence of C4mimTf2N tends to bring about significant enhancement in the extraction of Pu in both the acidic media (HCl and HNO3) as compared to that of using n-dodecane as diluent. The investigation of the extraction mechanism revealed that while using in RTIL (as diluent), the cation-exchange prevails up to 3M acidity, in contrast to anion exchange mechanism ruling above 3M acidic strength. However, in n-dodecane (as diluent) the metal extraction takes place via formation of anion-assisted neutral complex formation only at all acidities. Studies on the nature of species formed by Pu(IV) and BenzoDODA in both HNO3 and HCl medium showed formation of a di-solvate species for RTIL in contrast to mono-solvate formed in n-dodecane. Selectivity of BenzoDODA-RTIL system appears to be lost at lower acidities due to significant extent of extraction of other matrix elements along with target metal ion. However at higher nitric acid concentration (7M) BenzoDODA was found to be selectively extracting Pu(IV).

Evaluation of plutonium(IV) extraction rate between nitric acid and tri-n-butylphosphate solution using a glass chip microchannel.

Extraction of Pu(IV) with tri-n-butylphosphate is performed using a glass chip microchannel to evaluate the extraction rate. Two-phase flow forms in the microchannel by introducing a solution of Pu(IV) and tri-n-butylphosphate with flow rates above 5 μL/min. The Pu(IV) extraction reaction proceeds at the interface between the two phases. To evaluate the extraction rate, the contact time between the two phases is varied from 0.48 to 4.8 s by changing the confluent length of the microchannel and the flow rate. The Pu concentration of each phase collected from the microchannel is measured with an alpha liquid scintillation counter, and the contact time dependence of Pu(IV) extraction is obtained. An extraction model based on diffusion in the microchannel and the reaction at the interface is proposed and applied to determine the extraction rate. The extraction process is assumed to follow pseudo-first-order kinetics, and the extraction rate constant of Pu(IV) is determined to be 1.5 × 10(-2) cm/s. The investigation demonstrates that a microfluidic device can be a new tool to determine Pu(IV) extraction rates.

Investigations on Preferential Pu(IV) Extraction over U(VI) by N,N-Dihexyloctanamide versus Tri-n-butyl Phosphate: Evidence through Small Angle Neutron Scattering and DFT Studies

Straight chain amide N,N-dihexyloctanamide (DHOA) has been found to be a promising alternative extractant to tri-n-butyl phosphate (TBP) for the reprocessing of irradiated uranium- and thorium-based fuels. Unlike TBP, DHOA displays preferential extraction of Pu(IV) over U(VI) at higher acidities (≥3 M HNO3) and poor extraction at lower acidities. Density functional theory (DFT) based calculations have been carried out on the structures and relative binding energies of U(VI) and Pu(IV) with the extractant molecules. These calculations suggest that the differential hardness of the two extractants is responsible for the preferential binding/complexation of TBP to uranyl, whereas the softer DHOA and the bulky nature of the extractant lead to stronger binding/complexation of DHOA to Pu(IV). In conjunction with quantum chemical calculations, small angle neutron scattering (SANS) measurements have also been performed for understanding the stoichiometry of the complex formed that leads to relatively lower extraction of Th(IV) (a model for Pu(IV)) as compared to U(VI) using DHOA and TBP as the extractants. The combined experimental and theoretical studies helped us to understand the superior complexation/extraction behavior of Pu(IV) over U(VI) with DHOA.

Supercritical fluid extraction and separation of uranium from other actinides

The feasibility of separating U from nitric acid solutions of mixed actinides using tri-n-butylphosphate (TBP)-modified supercritical fluid carbon dioxide (sc-CO2) was investigated. The actinides U, Np, Pu, and Am were extracted into sc-CO2 modified with TBP from a range of nitric acid concentrations, in the absence of, or in the presence of, a number of traditional reducing and/or complexing agents to demonstrate the separation of these metals from U under sc-CO2 conditions. The separation of U from Pu using sc-CO2 was successful at nitric acid concentrations of less than 3M in the presence of acetohydroxamic acid (AHA) or oxalic acid (OA) to mitigate Pu extraction, and the separation of U from Np was successful at nitric acid concentrations of less than 1M in the presence of AHA, OA, or sodium nitrite to mitigate Np extraction. Americium was not well extracted under any condition studied.

PC-88A – impregnated polymeric beads: Preparation, characterization and application for extraction of Pu(IV) from nitric acid medium

Abstract The extractant-impregnated polymeric beads (EIPBs), containing polyethersulfone as base polymer and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) as an extractant, were prepared by phase inversion method. These EIPBs were characterized by FTIR, TGA and SEM techniques. The beads were found to have excellent acid stability, since these did not exhibit any structural deformation or loss of the extractant into aqueous nitric acid solution (6 M), for a period of 15 d. The feasibility of Pu(IV) extraction, using these beads, from nitric acid solution was tested by batch equilibration method. Parametric dependence of Pu(IV) extraction on experimental variables, like strength of nitric acid, equilibration time, Pu(IV) concentration, etc., was investigated. The present study also addressed the important practical issues, like maximum loading capacity and the reusability of these beads. Under optimized conditions, equilibrium capacity and maximum loading capacity for Pu(IV) were found to be 2.03 and 7.50 mg per gram of the swollen beads, respectively. The reusability of the beads was also ascertained by repetitive extraction-stripping of Pu(IV) up to 7 cycles of operation, without significant change in their extraction performance. The extraction of Pu(IV) by the blank polymeric beads was observed to be almost negligible, under the similar experimental conditions.

Tuning the Extractive Properties of Purex Solvent using Room Temperature Ionic Liquid

An Aliquat-336 based ionic liquid, namely, tri-n-octylmethylammonium bis(2-ethylhexyl)phosphate ([A3636]+[DEHP]−) was prepared and studied for the extraction of U(VI), Pu(IV), and Am(III) from nitric acid medium. Since the ionic liquid, [A336]+[DEHP]− was miscible in n-dodecane (n-DD), the extraction of these actinides in the PUREX solvent, 1.1 M tri-n-butylphosphate (TBP) in n-dodecane (n-DD), was investigated in the presence of small concentrations of ionic liquid. The distribution ratio of U(VI) and Am(III) in 0.03 M [A336]+[DEHP]−/n-DD decreased with increase in the concentration of nitric acid; whereas the extraction of Pu(IV) initially increased, it reached a maximum at 4 M nitric acid followed by the decrease. The extraction of actinides in ionic liquid medium decreased in the order Pu(IV) > U(VI) >> Am(III), indicating the feasibility of modifying the extractive properties of TBP/n-DD to favor Pu(IV) extraction. Therefore, the extraction of Pu(IV) in a solution of TBP – [A336]+[DEHP]− in n-DD was also studied. The distribution ratio of Pu(IV) increased with increase in the concentration of ionic liquid and decrease in the concentration of TBP in organic phase. The distribution ratio of Pu(IV) determined in the presence of small concentration of ionic liquid in 1.1 M TBP/n-DD was always much higher than that observed in 1.1 M TBP/n-DD. In contrast to this, the distribution ratio of U(VI) decreased by the addition of ionic liquid and Am(III) was inextractable even in the presence of ionic liquid.