Di(2-ethylhexyl)isobutyramide Research Articles

Extraction of Neptunium, Plutonium, Americium, Zirconium, and Technetium by Di-(2-Ethylhexyl)-Iso-Butyramide (DEHiBA) at High Metal Loadings

ABSTRACT Increased focus on carbon neutral energy has generated a resurgence of interest in nuclear power, and in particular advanced reactors which are likely to utilize high assay low enriched uranium (HALEU). This in turn could increase the economic attractiveness of recovering still partially enriched uranium from used nuclear fuel. Concomitant to development of advanced reactors, advanced reprocessing schemes should be developed which address the disadvantages to well established reprocessing schemes. The present study focuses on using di-(2-ethylhexyl)-iso-butyramide (DEHiBA) under high metal loading conditions for the reprocessing of used nuclear fuel. The elements examined in the study include the dominant transuranic actinides (Np, Pu, Am) as well as the often-problematic Tc and Zr. By increasing the concentration of the extractant from the more commonly reported 1.0 M – 1.5 M, the extraction of hexavalent actinides is substantially increased, while maintaining effective rejection of tri, tetra, and pentavalent actinides, particularly in the presence of high loadings of uranium. The extraction of Zr by 1.5 M DEHiBA is noted to be negligible by comparison to tributyl phosphate (TBP), however the coextraction of Tc with U is observed to be nominally twice the quantity that is extracted by TBP indicating a need for effective Tc management.

Radiation chemistry of the branched-chain monoamide di-2-ethylhexyl-isobutyramide

ABSTRACTThe radiolytic degradation of di-2-ethylhexyl-isobutyramide (DEHiBA) was examined by subjecting the compound to gamma irradiation, measuring the remaining concentration of the intact compound, identifying the degradation products, and measuring uranium distribution ratios. The combined effects of radiation dose, contact with aqueous solutions of HNO3, and aeration were also examined. The DEHiBA displayed significant stability at doses up to 1000 kGy, undergoing a slow exponential concentration decrease that was accompanied by the appearance of multiple degradation products. The most abundant compounds that were formed by radiolysis resulted from cleavage of the Ccarbonyl–N and Cethylhexyl–N bonds, generating di-ethylhexylamine and mono-ethylhexyl-isobutyramide. Acid contact did alter the radiolytic pathways, with acid favoring cleavage of the Ccarbonyl-N bond, while a more diverse array of compounds was formed in the absence of acid. Pulsed radiolysis experiments were also conducted, in which picosecond bursts of energetic electrons were used to irradiate solutions of dodecane containing DEHiBA; formation of the dodecane radical cation was implicated, which serially reacted with DEHiBA to form a radical or radical cation species intermediate in the formation of the observed products. The slow degradation kinetics suggests that DEHiBA possesses good potential for selective extraction of uranium in fuel cycle extraction operations.

Studies on the Extraction of Actinides Using a Solvent Containing D2EHiBA in Room Temperature Ionic Liquids: Unusual Extraction of the Tetravalent Ions

The extraction behavior of U(VI), Pu(IV), and Np(IV) from nitric acid medium has been studied using branched chain di(2-ethylhexyl)isobutyramide (D2EHiBA) dissolved in different room temperature ionic liquids (RTILs) [Cnmim][NTf2] (where n = 4, 6, or 8). Uranium extraction (DU) increased gradually with aqueous phase acidity for the three RTILs used in this study suggesting solvation mechanism. There was a reversal in the extraction behavior of Pu(IV) and Np(IV) from nitric acid medium using D2EHiBA dissolved in RTILs as solvents as compared to the behavior reported in the molecular diluent, n-dodecane, which shows negligible extraction of these metal ions. The extraction of Pu(IV) increased with aqueous phase acidity in different RTILs in the order: [C8mim][NTf2] > [C6mim][NTf2] > [C4mim][NTf2]. The distribution ratio values of these metal ions followed the order: DPu(IV) ≥ DNp(IV) > DU(VI) using D2EHiBA as extractant suggesting that RTILs can modify the extraction behavior of extractants.

Effect of successive alkylation of N,N-dialkyl amides on the complexation behavior of uranium and thorium: solvent extraction, small angle neutron scattering, and computational studies.

The effect of successive alkylation of the Cα atom adjacent to the carbonyl group in N,N-dialkyl amides (i.e., di(2-ethylhexyl)acetamide (D2EHAA), di(2-ethylhexyl)propionamide (D2EHPRA), di(2-ethylhexyl)isobutyramide (D2EHIBA), and di(2-ethylhexyl)pivalamide (D2EHPVA)) on the extraction behavior of hexavalent uranium (U(VI)) and tetravalent thorium (Th(IV)) ions has been investigated. These studies show that the extraction of Th(IV) is significantly suppressed compared to that of U(VI) with increased branching at the Cα atom adjacent to the carbonyl group. Small angle neutron scattering (SANS) studies showed an increased aggregation tendency in the presence of nitric acid and metal ions. D2EHAA showed more aggregation compared to its branched homologues, which explains its capacity for higher extraction of metal ions. These experimental observations were further supported by density function theory calculations, which provided structural evidence of differential binding affinities of these extractants for uranyl cations. The complexation process is primarily controlled by steric and electronic effects. Quantum chemical calculations showed that local hardness and polarizability can be extremely useful inputs for designing novel extractants relevant to a nuclear fuel cycle.

Selective recovery of uranium from THOREX feed by hollow fibre supported liquid membrane technique containing di(2-ethylhexyl) isobutyramide (D2EHIBA) as the carrier

Abstract Hollow fibre supported liquid membrane (HFSLM) studies were carried out for the selective recovery of uranium from THOREX feed solution (0.2 g/L U+200 g/L Th+0.03 M HF+0.1 M Al(NO3)3 at 4 M HNO3) using di(2-ethylhexyl) isobutyramide (D2EHIBA) as the carrier and distilled water as the strippant. About 85% of uranium was selectively transported into the receiver phase in 30 min with <1% contamination from thorium. On the other hand, under identical conditions of feed and strip solutions, about 90% of uranium was recovered in the same time when 5% TBP (tri-n-butyl phosphate) was used as the carrier, but a relatively large amount of thorium (>10%) was also co-transported to the product side. Strip phase acidity analysis revealed significant amount of acid co-transport with both the carriers. Acid transport was found to increase with the total salt content of the feed solution. The transport of metal ions was explained with the help of a theoretical model. Stability of the liquid membrane was also studied over about 5 d for long term reusability.

A novel technique for modifier free delivery of ligands for supercritical fluid extraction

A novel method has been developed for the controlled delivery of various ligands including solid extractants using supercritical carbon dioxide (Sc-CO2). A ligand delivery vessel with a restricted geometry where its inlet and outlet are located beside each other, accomplished the task of the controlled delivery of ligands. The proposed method eliminates the usage of modifier solvent such as methanol for the delivery of various ligands during the supercritical fluid extraction of metal ions. Using neat Sc-CO2, the delivery profiles for the various ligands such as octyl(phenyl)-N,N-diisobutylcarbamoylmethyl-phosphineoxide (CMPO), tri-n-butyl phosphate (TBP), tri-n-octyl phosphine oxide (TOPO), theonyltrifluroacetone (TTA) and di(2-ethylhexyl)isobutyramide (D2EHIBA) were established. The delivery profiles were optimised by investigating the influence of various extraction parameters such as ligand delivery vessel geometry, temperature, pressure, flow rate of Sc-CO2 and ligand content. Applications of these ligand delivery modes were demonstrated for the supercritical fluid extraction of uranium from tissue paper matrix and preferential extraction of uranium over thorium. These results are compared with the extraction studies involving methanol or hexane modifier under similar experimental conditions. The extraction of neodymium nitrate was also demonstrated using modifier free delivery mode.

Third phase formation studies in the extraction of Th(IV) and U(VI) by N,N-dialkyl aliphatic amides

N,N-dialkyl aliphatic amides with varying alkyl groups have been compared with organophosphorous extractants, tri- n-butyl phosphate (TBP) for third phase formation behavior during the extraction of Th(IV) and U(VI) from nitric acid medium. Dihexyl decanamide (DHDA) appears to be better in comparison to TBP with respect to third phase formation during thorium extraction. The effects of aqueous phase acidity and the nature of diluents on the third phase formation are studied. The limiting organic phase concentration (LOC) values for U(VI) and Th(IV) with branched chain, di(2-ethylhexyl) isobutyramide (D2EHIBA) increased with ligand concentration, while the critical aqueous concentration (CAC) values of metal ions decreased.

Transport studies of uranium across a supported liquid membrane containing N, N-di(2-ethylhexyl) isobutyramide (D2EHIBA) as the carrier

Di(2-ethylhexyl)isobutyramide (D2EHIBA) has been evaluated as a carrier for U/Th separation in supported liquid membrane. Microporous PTFE membrane was used as the polymeric support for the transport studies of uranium from a feed containing nitric acid. Effect of experimental parameters, viz. role of diluent, carrier concentration, feed acidity, metal ion concentrations on U/Th transport has been investigated. A model describing the transport mechanism has been proposed. Negligible transport of metal ions, such as Cs(I), Sr(II), Fe(III) and Eu(III) was observed under the optimised conditions. Reusability of membrane was also investigated.

N,N,N′,N′‐Tetraoctyl Diglycolamide (TODGA): A Promising Extractant for Actinide‐Partitioning from High‐Level Waste (HLW)

N,N,N′,N′‐Tetraoctyl diglycolamide (TODGA) has been evaluated as an extractant for the partitioning of minor actinides from simulated high level nuclear waste solutions. Acid uptake studies suggested that TODGA is more basic (KH: 4.1) as compared to TRUEX and DIAMEX solvents viz. CMPO (KH: 2.0) and DMDBTDMA (KH: 0.32), respectively. TODGA molecules display a tendency toward aggregation in n‐dodecane at lower acidities. Effect of diluent on the distribution behavior of Am(III) was studied employing diluents of different dielectric constants. N,N‐dialkyl amides with different alkyl groups viz. dibutyl decanamide (DBDA), di(2‐ethylhexyl) acetamide (D2EHAA), di(2‐ethylhexyl) propionamide (D2EHPRA), di(2‐ethylhexyl) isobutyramide (D2EHIBA), dihexyl octanamide (DHOA) and dihexyl decanamide (DHDA) were evaluated as phase modifiers. Distribution behavior of various metal ions viz. Am(III), Pu(IV), U(VI), Eu(III), Fe(III), Sr(II) and Cs(I) was studied from pure nitric acid solution as well as from simulated high level waste solution.

Role of Ligand Structure and Basicity on the Extraction of Uranyl Isoxazolonate Adducts

The extraction behavior of uranium(VI) from dilute nitric acid was investigated employing 3‐phenyl‐4‐acetyl‐5‐isoxazolone (HPAI) as the chelating ligand and several amides with varying degree of branching such as di‐2‐ethylhexylacetamide (D2EHAA), di‐2‐ethylhexylpropanamide (D2EHPrA), di‐2‐ethylhexylisobutyramide (D2EHiBA), and di‐2‐ethylhexylpivalamide (D2EHPvA) as neutral donors in toluene medium. The two‐phase extraction constant (log K ex) for the binary species UO2(PBI)2H2O was found to be 0.66. The overall equilibrium constants (log K ) for the ternary species of the type UO2(PAI)2B are estimated to be 5.29 (D2EHAA), 5.02 (D2EHPrA), 4.86 (D2EHiBA), and 4.28 (D2EHPvA), respectively, which vary linearly with the basicity of the amides. The role of steric factors in the co‐ordination of the amides to the uranyl β‐diketones and the adduct formation in the case of the ternary complexes was explained on the basis of molecular modeling.

Distribution Behavior of U(VI), Th(IV), and Fission Products with Di(2-ethylhexyl) Isobutyramide under Process Conditions

Branched-chain di(2-ethylhexyl) isobutyramide (D2EHIBA) has been chosen as a promising alternative to tri-n-butyl phosphate (TBP) for the recovery of 233 U from irradiated Th. Laboratory batch studies as well as mixer settler studies have been performed under THOREX feed conditions with D2EHIBA as well as with TBP. Significant improvement in the separation of 233 U from Th and fission products has been achieved by employing 0.5 M D2EHIBA in n-dodecane as compared to that of 5% TBP (the THOREX solvent). Mixer settler runs have demonstrated that loss of uranium to the raffinate and thorium uptake toward organic phase is lower in the case of 0.5 M D2EHIBA than in that of 5% TBP. Final purification of uranium from U/Th mixture has been carried out via cation-exchange resin.

Pu-Th separation studies employing di(2-ethylhexyl)isobutyramide (D2EHIBA) as extractant from nitric acid medium

Summary An attempt has been made to explore the use of di(2-ethylhexyl)isobutyramide (D2EHIBA) as an extractant for the recovery of Pu from the (proposed) AHWR fuel fabrication scrap solution. The extraction of Pu in the hexavalent state has been found to be distinctly more efficient than that in the tetravalent state. Distribution studies have been carried out by maintaining Pu as Pu(VI) employing AgO as the oxidant. Scrubbing at 5M HNO3 has been proposed to reduce the interference due to the co-extracted Th(IV). Quantitative stripping of the extracted Pu was achieved using Hydroxyl Ammonium-Nitrate (HAN) as reductant. Ion exchange studies have been carried out for the final purification of Pu. It is proposed to employ the cation exchanger, Biorad AG 50X8 for the final purification of Pu from the stripped solution, keeping Pu as Pu(III).

The role of oxidants in Pu-Th separation studies employing di(2-ethylhexyl)isobutyramide (D2EHIBA) as extractant

Summary Distribution studies of Pu and Th have been carried out under varying acidity/ligand concentrations to optimise the conditions for their separation employing di(2-ethylhexyl)isobutyramide (D2EHIBA) in n-dodecane as extractant. In view of the selective complexation of D2EHIBA towards hexavalent metal ions over tetravalent metal ions, the focus of the present work is to identify a suitable oxidant of Pu. Amongst various oxidising agents investigated for the oxidation of Pu to Pu(VI), AgO appears to be a promising candidate as (i) it is thermodynamically as well as kinetically a favourable oxidant and (ii) unlike Cr(VI) and Ce(IV), it is not co-extracted with Pu towards the organic phase.

Extraction of Ternary Beta‐Diketonates of Uranyl Ion Using Some Substituted Monoamides

The extraction behavior of uranyl ion from dilute nitric acid medium employing 1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone (HPMBP)/2‐thenoyl‐ trifluoroacetone (HTTA) in toluene and their mixture with several structurally modified monoamides viz. di‐2‐ethylhexyl acetamide (D2EHAA), di‐2‐ethylhexyl propanamide (D2EHPrA), di‐2‐ethylhexyl isobutyramide (D2EHiBA), and di‐2‐ethylhexyl pivalamide (D2EHPvA) was investigated. The species of the type UO2(A)2 and UO2(A)2·B were extracted for the binary and ternary extraction systems respectively where A = PMBP/TTA and B = D2EHAA, D2EHPrA, D2EHiBA, or D2EHPvA. The extraction constants (log K ex) for the binary species UO2(A)2 were determined to be −2.32 ± 0.03 for HTTA and 0.21 ± 0.02 for HPMBP, which was an inverse function of their pK a value. The overall extraction constants (log K) for the ternary species UO2(A)2·B were determined as 4.70, 4.22, 4.00, 3.61, 2.65, 2.39, 2.32, and 1.76 for UO2(PMBP)2·D2EHAA, UO2(PMBP)2·D2EHPrA, UO2(PMBP)2·D2EHiBA, UO2(PMBP)2·D2EHPvA, UO2(TTA)2·D2EHAA, UO2 (TTA)2·D2EHPrA, UO2(TTA)2·D2EHiBA, and UO2(TTA)2·D2EHPvA, respectively. A linear correlation was observed between the basicity of the amide and the corresponding adduct's formation constants.

Effect of structure of N,N dialkyl amides on the extraction of U(VI) and Th(IV): a thermodynamic study

The temperature effect on the extraction behaviour of U(VI) and Th(IV) from 3 M HNO3 employing 1 M solutions of N,N diallkyl amides with varying alkyl substituents on the Cα atom viz. di(2-ethylhexyl)acetamide (D2EHAA), di(2-ethylhexyl)propionamide (D2EHPRA), di(2-ethylhexyl)isobutyramide (D2EHIBA) and di(2-ethylhexyl)pivalamide (D2EHPVA) in n-dodecane has been investigated. These studies indicate that the extraction reactions of U(VI) and Th(IV) are enthalpy stabilised while the entropy factor counteracts the extraction. An attempt has been made to correlate the thermodynamic parameters with the structure of the extractant molecules.

STRUCTURAL EFFECTS IN N,N-DIALKYL AMIDES ON THEIR EXTRACTION BEHAVIOR TOWARD URANIUM AND THORIUM

Extraction behavior of four N,N-dialkylamides with varying alkyl substituents on the α carbon atom with respect to carbonyl group, viz. di-(2-ethylhexyl)acetamide (D2EHAA), di-(2-ethylhexyl)propionamide (D2EHPRA), di-(2-ethylhexyl)isobutyramide (D2EHIBA), and di-(2-ethylhexyl)pivalamide (D2EHPVA) toward nitric acid, U(VI), and Th(IV) has been investigated. The conditional acid uptake constant (K H) values for 1:1 species predominant in the acidity range 0.5–3 M HNO3 are in the following order: D2EHAA (0.28±0.03) > D2EHPRA (0.20±0.01) > D2EHIBA (0.15±0.04) > D2EHPVA (0.06±0.002). The stoichiometry of the extracted species of uranium conforms to UO2(NO3)2·2A (where A = amide). The conditional extraction constants (K ex.) for uranium were found to vary in the following order: 34.0±2.0 (D2EHAA) > 5.6±0.4 (D2EHPRA) > 1.2±0.1 (D2EHIBA)>0.51±0.03 (D2EHPVA). Third phase has been observed in the case of D2EHAA (≥1 M HNO3) and D2EHPRA (≥3 M HNO3) in the presence of macro concentration of thorium (220 g/L). The separation factor (S.F.=,D U/D Th) values of D2EHPVA are distinctly larger as compared to other amides as well as to TBP. An attempt has also been made to correlate the observed distribution data with the electronic charge parameter of the amide extractants.

DISTRIBUTION BEHAVIOUR OF U(VI), Th(IV) AND Pa(V) FROM NITRIC ACID MEDIUM USING LINEAR AND BRANCHED CHAIN EXTRACTANTS

ABSTRACT The extraction behaviour of 1M solutions of tri-2-ethylhexyl phosphate (TEHP), di-2-ethyl hexyl isobutyramide (D2EHIBA), tri-n-butyl phosphate (TBP) and di-n-hexyl hexanamide (DHHA) in n-dodecane towards U(VI), Th(IV) and Pa(V) in the presence of 220 g/L of Th from nitric acid medium has been studied. The limiting organic concentrations (LOC) of thorium (g/L) for 1 M TBP and 1 M DHHA are evaluated as 31, 20 ( at 1 M HNO3) and 25,13 (at 4 M HNO3) respectively. The distribution ratio (D) values of U(VI), Th(IV) and Pa(V) in the presence of thorium (220 g/L) at. 1 M HNO3 suggest that branching in the alky group of amides suppresses the extraction considerably. In view of the selective extraction of U over Th by 5 % TBP in THOREX process at 4 M HNO3, distribution behaviour is also studied employing a lower concenfration (0·18 M) of extractant for comparison purpose, Separation factor (S. F.) values for U(VI) over Th(IV) under different experimental conditions consistently varied in the order: D2EHIBA > DHHA > TEHP > TBP. The quantitative extraction of 233U from a synthetic mixture containing 233U (10−5 M). 233Pa (10−11 M) and thorium (220 g/L) at 1 M HNO3 using 1 M solution of D2EHIBA in n-dodecane is achieved in three stages, Stripping and reusability studies of D2EHIBA have also been carried out.

Solvent Extraction Studies on Th(IV), Pa(V) and U(VI) from Nitric Acid Medium using Di-2-Ethyl Hexyl Isobutyramide (D2EHIBA)

Article Solvent Extraction Studies on Th(IV), Pa(V) and U(VI) from Nitric Acid Medium using Di-2-Ethyl Hexyl Isobutyramide (D2EHIBA) was published on August 1, 1999 in the journal Radiochimica Acta (volume 86, issue 3-4).

Separation Studies of Uranium and Thorium Using Di-2-Ethylhexyl Isobutyramide (D2EHIBA)

The extraction behavior of di-2-ethylhexyl isobutyramide (D2EHIBA) in dodecane medium for U(VI), Th(IV), and fission products such as Zr, Ce, Eu, and Cs, and the structural material Fe, has been investigated over a wide range of nitric acid concentrations. It has been observed that whereas D U varies from < 10−3 (pH 2.0) to 4.4 (6 M HNO3) with 1 M ligand, the corresponding D Th values are 1.5 × 10−3 and 4 × 10−2. In the presence of 250 g/L of Th, D U values are 8.6 (pH 2.0) and 2.2 (6 M HNO3). D2EHIBA has been found to be a promising extractant of trace concentrations of U in the presence of macro amounts of Th. The extraction of fission products and Fe is found to be negligible. D2EHIBA is found to extract nitric acid predominantly as a 1:1 species (K H = 0.156 ± 0.048). U(VI) is extracted as a disolvate UO2(NO3)·2D2EHIBA (K ex = 0.87 ± 0.08).

Di(2-ethyl hexyl) butyramide and di(2-ethyl hexyl)isobutyramide as extractants for uranium(VI) and plutonium(IV)

The extraction of uranium(VI) and plutonium(IV) from nitric acid into n-dodecane was studied using two isomeric branched alkyl amides, di(2-ethyl hexyl) butyramide (DEHBA) and di(2-ethyl hexyl) isobutyramide (DEHIBA). The extraction ratios of Pu(IV) at relatively high acidities were higher than the corresponding values for U(VI) in the case of DEHBA. However, with DEHIBA the values for Pu(IV) were negligibly small. Pu(IV) was found to be extracted as trisolvate by DEHBA and as disolvate by DEHIBA. U(VI) was extracted by both the amides. From the study of the extraction reactions at different temperatures, it was shown that all the reactions in the present investigation were enthalpy favoured and entropy disfavoured. Separation of Pu(IV) from bulk of U(VI) was feasible. However, the purity of the separated plutonium was not satisfactory in batch extraction studies.