Distribution Behavior of Neptunium by Extraction with N,N-dialkylamides (DEHDMPA and DEHBA) in Mixer-Settler Extractors

The extraction properties of N,N-di(2-ethylhexyl)-2,2-dimethylpropanamide (DEHDMPA) and N,N-di(2-ethylhexyl)butanamide (DEHBA) for Np(V) and Np(VI) were studied by a batch method using various nitrate ion concentrations. The distribution ratios of Np(VI) obtained with DEHDMPA and DEHBA exceeded unity when the nitrate ion concentration was > 3 mol/dm³, while DEHDMPA and DEHBA barely extracted Np(V). A continuous counter-current experiment using mixer-settler extractors was performed to evaluate the behavior of Np in a process comprising two cycles using DEHDMPA and DEHBA as extractants. The feed was nitric acid containing U, Pu, Np, and several fission products. The results indicated that part of Np(V) changed its valence state to Np(IV) or Np(VI) after the 1st experimental cycle. The recoveries of Np in the streams of U fraction and U-Pu fraction were 63.7% and 29.1%, respectively.     

Recovery of U and Pu from Nitric Acid using N,N-di(2-ethylhexyl)butanamide (DEHBA) in Mixer-Settler Extractors

The recovery of U and Pu from nitric acid using N,N-di(2-ethylhexyl)butanamide (DEHBA) in mixer-settler extractors was calculated by a simulation code, and a continuous counter-current experiment using mixer-settler extractors was performed. The flow rate, stage number, and nitric acid concentration were chosen as the parameters for the calculation, and the simulation code provided appropriate experimental conditions for separating U from Pu. The continuous counter-current experiment was carried out with three mixer-settler extractors consisted of the following 5 steps: U–Pu extraction (6 stages), Scrub (10 stages), U recovery (6 stages), Pu back-extraction (10 stages), and U back-extraction (16 stages). The results of the continuous counter-current experiment showed that the percentages of U and Pu extracted using 1.5 mol/dm³ (M) DEHBA from 4 M nitric acid were > 99.9% and 97.84%, respectively. Extracted Pu was back-extracted to the aqueous phase via contact with 0.15 M nitric acid, while most of the U content remained in the organic phase. Uranium in the organic phase was then back-extracted via contact with 0.01 M nitric acid, and the percent of U in the U fraction stream was 96.06%. The percentages of U and Pu in the Pu fraction stream were 3.94 % and 97.48%, respectively.     

Evaluation of two-phase separation in N,N-di(2-ethylhexyl)butanamide-nitric acid systems using turbidity measurements

Quantitative evaluation of the two-phase separation between N,N-di(2-ethylhexyl)butanamide (DEHBA) and tri-n-butyl phosphate (TBP) diluted with n-dodecane and uranyl nitrate solution in nitric acid medium was achieved using turbidity measurements. The turbidities of DEHBA were relatively high, particularly at high DEHBA concentrations, while that of TBP rapidly decreased irrespective of nitric acid concentration. A high concentration of DEHBA, nitric acid, and uranium increased the turbidities in the organic phase, which could be ascribed to the increase in viscosity. Distribution ratios of uranium were also measured, and it was indicated that turbidity did not have a critical effect on the distribution ratio when the turbidity was below a certain value.     

Synthesis and Evaluation of N,N′-dimethyl-N,N′-dicyclohexyl-Malonamide (DMDCMA) as an Extractant for Actinides

A malonamide based extractant, i.e., N,N′-dimethyl-N,N′-dicyclohexyl-malonamide (DMDCMA) was synthesized in a single step and tested for the extraction of several actinide ions such as Am(III), U(VI), Np(IV), Np(VI), Pu(IV), Pu(VI), etc., from nitric acid medium. The extractant was soluble in phenyltrifluoromethylsulphone (PTMS or FS-13) unless stated otherwise. The effect of various experimental parameters, such as the aqueous phase acidity (0.01–3 M HNO₃), nature of the acid, oxidation states of the metal ions, ligand concentration, nature of the diluent and temperature on the extraction behavior of metal ions was studied. The extracted Am(III) species was determined from slope analysis method as [Am(NO₃)₃(DMDCMA)₂]. The extraction of the metal ions was found to increase with the aqueous phase acidity. The temperature variation studies allowed the calculation of the heat of the two-phase extraction reaction as well as the corresponding extraction constants. These studies revealed that DMDCMA showed good extraction for all the actinide metal ions investigated, and have the advantage of single stage synthesis and easier purification protocol.     

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.     

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) [C_nmim][NTf₂] (where n = 4, 6, or 8). Uranium extraction (D_U) 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: D_Pu(IV) ≥ D_Np(IV) > D_U(VI) using D2EHiBA as extractant suggesting that RTILs can modify the extraction behavior of extractants.     

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.     

Separation of U(VI) and Th(IV) from Nd(III) by Cross-Current Solvent Extraction Mode Using Tri-iso-amyl Phosphate as the Extractant

Separation of U(VI) and Th(IV) from Nd(III) in nitric acid media with solutions of tri-iso-amyl phosphate (TiAP) in n-dodecane has been studied by batch extraction in cross-current mode to evaluate the feasibility of employing TiAP as an alternate extractant to tri-n-butyl phosphate (TBP) for monazite ore processing. The interference of U(VI), Th(IV), and Nd(III) in the presence of each other during their analyses by titrations has also been validated in the present study. The extraction studies substantiate that the high solvent loading conditions can be achieved without organic phase splitting in the extraction from concentrated feed solutions with TiAP based solvents, whereas TBP forms third phase under such conditions. The separation factor for Th(IV) with respect to Nd(III) can be improved with TiAP as the extractant and by carrying out the extraction with feed solution in 8 M HNO₃. Solvent extraction studies conducted with solutions of U(VI), Th(IV), and Nd(III) in nitric acid media by TBP and TiAP revealed the identical extraction, scrubbing, and stripping behavior of both the extractants with respect to U(VI), Th(IV), and Nd(III). The results insinuate that TiAP can be used as an alternate extractant to TBP for the separation of U(VI) and Th(IV) from monazite ores. The data generated in the present study can be exploited for the development of flow sheets using TiAP based solvents to separate U(VI) and Th(IV) from rare earths for the processing of monazite leach solutions.     

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.     

Comparison of Extraction Behavior of Neptunium from Nitric Acid Medium Employing Tri-n-Butyl Phosphate and N,N-dihexyl Octanamide as Extractants

Extraction behavior of neptunium has been compared for tri-n-butyl phosphate (TBP) and N,N-dihexyl octanamide (DHOA) extractants as a function of nitric acid concentration (0.5 ? 6 M HNO₃), uranium loading (50 and 300 g/L relevant to Pu rich fast reactor and Pressurized Heavy Water Reactor, PHWR spent fuels, respectively), and in the presence of oxidizing and reducing agents. These studies suggest the possibility of co-recovery of U(VI), Pu(IV) and Np(IV) from spent fuel dissolver solutions (of Pu rich fuels) employing DHOA as extractant.     

TETRA-BUTYL-MALONAMIDE AND TETRA-ISOBUTYL MALONAMIDE AS EXTRACTANTS FOR URANIUM(VI) AND PLUTONIUM(IV)

ABSTRACT

Two new symmetrical diamides, namely straight-chain alkyl substituted neutral tetra-butyl-malonamide(TBMA) and sterlcally hindered branched-chain alkyl substituted tetra-isobutyl malonamide(TIBMA) were synthesised, characterised and used for the extraction of U(VI) and Pu(IV) from nitric acid media into n-dodecane. Both the cations were found to be extracted as their disolvates. Interestingly TBMA extracted more efficiently than TIBMA but afforded poor selectivity for Pu/U separation. The thermodynamic parameters involved in the extraction, determined by the temperature variation method, indicated the reactions in all cases to be enthalpy favoured. Entropy was found to be counteracting the extraction of U(VI) and favouring the extraction of Pu(IV). The recovery of diamides from the loaded actinides could be easily accomplished by using dilute oxalic acid or dilute U(IV) as the strippant for Pu(IV) and using dilute Na₂C0₃ as that for U(VI).     

Comparative Evaluation of Tri-n-butyl Phosphate (TBP) and Tris(2-ethylhexyl) Phosphate (TEHP) for the Recovery of Uranium from Monazite Leach Solution

Separation of U(VI) from Th(IV) and rare earth elements (REEs) present in monazite leach solution (nitric acid medium) has been studied using tris(2-ethylhexyl) phosphate (TEHP) and tri-n-butyl phosphate (TBP) dissolved in n-paraffin as solvents under varying experimental conditions such as nitric acid, extractant and metal ion concentrations etc. There is an increase in distribution ratio of U(VI) (D _U ) with increase in aqueous phase acidity up to 5 M HNO₃ beyond which a decrease is observed. Typically for 1 × 10^?3 M U(VI), the D_U values increase from 8 (0.5 M HNO₃) to 80 (5 M HNO₃) for 1.1 M TEHP, and from 2 (0.5 M HNO₃) to 43 (5 M HNO₃) for 1.1 M TBP in n-paraffin. The separation factors of U(VI) (β: D_U/D_M) over metal ions (M) such as Th(IV) and Y(III) (chosen as a representative of heavy REEs) are better for TEHP than TBP at all nitric acid concentrations. Batch solvent extraction data have been used to construct the McCabe-Thiele diagrams for the recovery of U(VI) employing TEHP as the extractant. A process flow sheet has been proposed with 0.2 M TEHP in n-paraffin as solvent for the recovery of U(VI) from simulated monazite leach solution in HNO₃ medium.     

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.     

Uranium Permeation Studies from Nitric Acid Medium across Supported Liquid Membrane Impregnated with PC88A and its Mixtures with Neutral Oxodonors in n-paraffin as Carriers

The permeation of U(VI) from nitric acid medium using supported liquid membrane (SLM) technique has been studied employing varying compositions of feed (uranium concentration and acidity), carrier, and receiving phase. Microporous polytetrafluoroethylene (PTFE) membranes were used as a solid support and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) either alone or as a mixture of neutral donors like tri-n-butyl phosphate (TBP), tris(2-ethylhexyl) phosphate (TEHP), and tri-n-octyl phosphine oxide (TOPO) dissolved in n-parrafin as the carrier. Oxalic acid/Na₂CO₃ solutions were used as the receiving phase. The permeability coefficient (P) of U(VI) decreased with increased nitric acid concentration up to 3 M HNO₃ and thereafter increased up to 5 M HNO₃. Uranium permeation was also investigated from its binary mixtures with other metal ions such as Zr(IV), Th(IV), and Y(III) at 2 M HNO₃ employing 0.1 M PC88A/n-paraffin as the carrier, and 0.5 M oxalic acid as the receiver phase. The presence of neutral donors in the carrier solution enhanced the permeation of U(VI) across the SLM in the following order: TEHP ～ TBP > TOPO using 0.1 M oxalic acid as receiver phase. There was significant enhancement in uranium transport for feed acidity ≤2 M HNO₃ employing 1 M Na₂CO₃ as the receiver phase. These studies suggested that 0.1 M PC88A and 0.5 M oxalic acid as carrier and receiver phases appear suitable for selective and faster transport of uranium from the uranyl nitrate raffinate (UNR) waste solutions.     

Co-Extraction of U(VI) and HNO3 Using TBP and its Higher Homologues TiAP and TEHP: Comparison of Equilibria,Kinetics, and Rate of Extraction

In this work, bulk-liquid membrane (BLM) system is used to compare tri-n-butyl phosphate (TBP), tri-isoamyl phosphate (TiAP), and tris(2-ethylhexyl) phosphate (TEHP) for their relative ability to co-extract U(VI) and nitric acid from aqueous nitric acid feed-phase into water strip-phase, through hydrocarbon membrane-phase. The kinetics of extraction is modelled and the model is validated through experiments. The quantity which determines the efficiency of liquid emulsion membrane (LEM) process is the relative rate of extraction of U(VI) to nitric acid. This is in the order TiAP>TEHP>TBP, indicating that TiAP is most suitable for extraction of U(VI) from nitric acid using LEM.     

Gel-Liquid Extraction and Separation of U(VI), Th(IV), Ce(lll), and Co(ll)

Abstract

The gel-liquid extraction of U(VI), Th(IV), Ce(III), and Co(II) has been investigated in the 0.01 to 2 M HNO₃ range using a gel prepared by swelling styrene divinylbenzene with di-(2-ethylhexyl)phosphoric acid. Obtained results indicate that all of the tested cations can be extracted and that the extraction coefficients increase in the order Ce(III) < Co(II) < Th(IV) < U(VI) and generally decrease with acidity. Under suitable conditions, separation of Th(IV), Ce(III), or Co(II) from U(VI) or of Th(IV) from Ce(III) can be achieved. Kinetic studies indicate that the extraction process is controlled by a progressive shell sorption mechanism.     

Solvent Extraction Behavior of Plutonium (IV) Ions in the Presence of Simple Hydroxamic Acids

Abstract

Formo‐ and aceto‐hydroxamic acids are very effective reagents for stripping Pu(IV) ions from a tri‐butyl phosphate phase into nitric acid. Distribution data for Pu(IV) in the presence of these hydroxamate ions have been obtained and trends established. The affinity of aceto‐hydroxamic acid for Pu(IV) ions and its selectivity over U(VI) ions is demonstrated by the values of the stability constants in HClO₄. These data support the applications of simple hydroxamic acids in advanced Purex‐type solvent extraction systems.     

Extraction Behavior of Some Actinides and Fission Products from Nitric Acid Medium by a New Unsymmetrical Diglycolamide

Abstract

A new unsymmetrical diglycolamide, N,N-di-2-ethylhexyl-N',N'-di-octyl-3-oxapentane-1,5-diamide, trivially known as di-ethylhexyl-di-octyl-diglycolamide (DEHDODGA) has been synthesized, and characterized by ¹H, and ¹³C nmr, mass, and IR spectroscopy. Extraction behavior of ²⁴¹Am(III), ^(152+154)Eu(III), ²³⁹Pu(III), ²³⁹Pu(IV), ²³³U(VI), ¹³⁷Cs(I), and ^(85+89)Sr(II) from nitric acid medium by a solution of DEHDODGA in n-dodecane was studied, at 298–333 K. The effect of concentrations of HNO₃ and DEHDODGA and of temperature on the distribution ratio (D _M) was studied. Extraction of Eu(III), Am(III), Pu(III), and Pu(IV) increased with increase in nitric acid concentration, and the distribution ratio of Cs(I) was insignificant. However, the distribution ratios of U(VI) and Sr(II), though not insignificant, but was quite less compared to trivalents, and Pu(IV). The D _Sr(II) increased with increase in the concentration of nitric acid, reaching a maximum at 4 M followed by decrease. The stoichiometry of Am(III) – DEHDODGA was determined by slope analysis of extraction data, and the enthalpy change accompanied by the extraction of Eu(III), Pu(III), and Am(III) was determined and reported in this article.