Development and Demonstration of Americium (III)-Europium (III) Separation Using Diglycolamic Acid

The extraction behavior of Eu(III) and Am(III) in a solution of bis(2-ethylhexyl)diglycolamic acid (HDEHDGA) in n-dodecane (n-DD) from citric acid (CA) medium was studied as a function of various parameters. The extraction increased with increase of pH, reached a maximum at pH 2 followed by decrease. The stripping behavior of Eu(III) and Am(III) from the loaded organic phase was studied by using a solution of diethylenetriaminepentaacetic acid (DTPA) and CA. The conditions needed for the efficient separation of Am(III) from Eu(III) were optimized. Based on the optimized conditions, the feasibility of separating Am(III) from Eu(III) present in CA feed solution was investigated in a 20- stage mixer-settler. Quantitative extraction of Eu(III) and Am(III) in 0.1 M HDEHDGA/n-DD was achieved in 3–4 stages, whereas the selective back extraction of Am(III) was achieved in ～20 stages upon contacting the loaded organic phase with a stripping formulation composed of DTPA-CA at pH 1.5. The results confirmed the possibility of using diglycolamic acid for the separation of trivalent actinides from the chemically similar lanthanides, which is indeed necessary for transmutation of minor actinides present in high-level liquid waste (HLLW).     

Actinide(III)/Lanthanide(III) Separation Via Selective Aqueous Complexation of Actinides(III) using a Hydrophilic 2,6-Bis(1,2,4-Triazin-3-Yl)-Pyridine in Nitric Acid

i-SANEX is a process for separating actinides(III) from used nuclear fuels by solvent extraction: Actinides(III) and lanthanides(III) are co-extracted from a PUREX raffinate followed by selective back extraction of actinides(III) from the loaded organic phase. This step requires a complexing agent selective for actinides(III). A hydrophilic sulfonated bis triazinyl pyridine (SO₃-Ph-BTP) was synthesized and tested for selective complexation of actinides(III) in nitric acid solution. When co-extracting Am(III) and Eu(III) from nitric acid into TODGA, adding SO₃-Ph-BTP to the aqueous phase suppresses Am(III) extraction while Eu(III) is extracted. Separation factors in the range of 1000 are achieved. SO₃-Ph-BTP remains active in nitric acid up to 2 mol/L. As a result of this performance, buffering or salting-out agents are not needed in the aqueous phase; nitric acid is used to keep the lanthanides(III) in the TODGA solvent. These properties make SO₃-Ph-BTP a suitable candidate for i-SANEX process development.     

Extraction behavior of Am(III) and Eu(III) by tri-n-octylmethylammonium diglycolamate ionic liquid impregnated XAD-7

Aliquat-336-based strongly hydrophobic ionic liquid, tri-n-octylmethylammonium diglycolamate ([A336]⁺[DGA]^?), was prepared and impregnated in Amberlite XAD-7 (abbreviated as [A336]⁺[DGA]^?/XAD-7) for studying the extraction behavior of Am(III) and Eu(III) from nitric acid medium. The distribution ratio of Am(III) and Eu(III) in [A336]⁺[DGA]^?/XAD-7 decreased with an increase in the concentration of nitric acid and the mechanism of trivalent metal ion extraction in the resin phase was elucidated. The uptake of Am(III) and Eu(III) in [A336]⁺[DGA]^?/XAD-7 followed a second order and from the Langmuir adsorption model the apparent europium extraction capacity was determined. The conditions needed for efficient separation of Am(III) from Eu(III) was optimized.     

Separation of La(III), Eu(III), and Ho(III) with Sorbents Impregnated by Mixtures of Acidic Phosphoryl Podands and Amines in Nitric Acid Solutions

ABSTRACT

The possibility of separation of La(III), Eu(III), and Ho(III) as respective individual representatives of light, medium, and heavy rare earth elements was studied using sorbents impregnated by mixtures of acidic phosphoryl podands derived from diethylene glycol and octyl, dioctyl, and trioctyl amines from nitric acid solutions of various concentrations. The influence of the phosphoryl podands structure, their percentage content, and proportion in a sorbent and the nature of an acid on the efficiency of separation of La(III), Eu(III), Ho(III) was studied. It is shown that the greater is the concentration of HNO₃, the smaller are the separation factors of REEs, and remarkably so. The most efficient separation is achieved with the concentration of HNO₃ not over 0.04 mol/L. The optimal conditions of separation of La(III), Eu(III), and Ho(III) with the developed sorbent were found. Repeated use of the sorbent for the separation of La(III), Eu(III), and Ho(III) after its regeneration with 0.04 mol/L HNO₃ was estimated. It was found that the efficiency of separation of REEs with the sorbents impregnated by a mixture of 1,5-bis(2-oxyethoxyphosphoryl-4-ethylphenoxy)-3-oxapentane and trioctylamine (TOA) exceeds markedly that made of a mixture of di-(2-ethylhexyl)phosphoric acid (DEHPA) and TOA.     

Adsorption of Eu(III), Th(IV), and U(VI) by mesoporous solid materials bearing sulfonic acid and sulfamic acid functionalities

ABSTRACT

SBA-15 mesoporous materials modified by sulfonic acid and sulfamic acid functionalities, abbreviated as SBA-15/SO₃H and SBA-15/NHSO₃H, were synthesized and applied for the removal–separation of Eu(III), Th(IV), and U(VI). SBA-15/NHSO₃H showed an excellent selectivity toward U(VI), while SBA-15/SO₃H was more efficient adsorbent for Eu(III) and Th(IV). It was found that in the presence of KNO₃ (1 mol L^?1), the separation of Eu(III)/Th(IV) from their mixtures is possible. The results of the sorption behavior indicated a high adsorption capacity toward U(VI) and Th(IV) ions (140.5 and 106.7 mg g^?1, respectively) and ultrafast kinetics (15 min) in Eu(III) adsorption.     

Solvent Extraction and Fluorescence Spectroscopic Investigation of the Selective Am(III) Complexation with TS-BTPhen

An americium(III) selective separation procedure was developed based on the coextraction of trivalent actinides (An(III)) and lanthanides (Ln(III)) by TODGA (N,N,N′,N′-tetraoctyl-diglycolamide), followed by Am(III) selective stripping using the hydrophilic complexing agent TS-BTPhen (3,3′,3?,3?′-[3-(1,10-phenanthroline-2,9-diyl)-1,2,4-triazine-5,5,6,6-tetrayl]tetrabenzenesulfonic acid). Distribution ratios were found at an acidity of 0.65 mol L^?1 nitric acid that allowed for the separation of Am(III) from Cm(III) (D_Cm > 1; D_Am < 1), giving a separation factor between curium and americium of SF_Cm/Am = 3.6 within the stripping step. Furthermore, Am(III) was readily separated from the lanthanides with the lowest selectivity for the Ln(III)/Am(III) separation being lanthanum with a separation factor of SF_La/Am = 20. The influence of the TS-BTPhen concentration on Am(III) distribution ratios was studied, giving a slope (logD vs. log[TS-BTPhen]) of approximately ?1 for the stripping of An(III) with TS-BTPhen from the TODGA-based organic phase. Time-resolved laser fluorescence spectroscopy (TRLFS) measurements of curium(III) were used to analyze the speciation of Cm(III)-TS-BTPhen complexes. Both 1:1 and 1:2 complexes were identified in single-phase experiments. The formation of the 1:1 complex was suppressed in 0.5 mol L^?1 nitric acid but it was significantly present in HClO₄ at pH 3. Conditional stability constants of the complex species were calculated from the TRLFS experiments.     

Factors Affecting on the Sorption/Desorption of Eu (III) using Activated Carbon

Abstract

The sorption and desorption of Eu (III) on H‐APC activated carbon using a batch technique has been studied as a function of carbon type, shaking time, initial pH solution, temperature, particle size of carbon, and concentration of the adsorbent and the adsorbate. The influence of different anions and cations on adsorption has been examined. The experimental data have been analyzed by Langmuir, Freundlich, and Temkin sorption isotherm models and the adsorption data for Eu (III) onto activated carbon were better correlated to the Temkin isotherm and the maximum absorption capacities obtained was 46.5 mg g^?1. Anions of phosphate, carbonate, oxalate, and acetate were found to increase the adsorption of Eu (III), whereas nitrate, chloride and all studied cations, potassium, sodium, calcium, magnesium, and aluminum have a negative effect on the adsorption capacity. More than 99% europium adsorbed on H‐APC eluted with 0.5 M HCl solution. The activated carbon prepared from apricot stone using 70% H₃PO₄ could be considered as an adsorbent that has a commercial potential for Eu (III) treatment.     

Extraction of Lanthanides(III) and Am(III) by Mixtures of Malonamide and Dialkylphosphoric Acid

Abstract

N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide, DMDOHEMA, and di‐n‐hexylphosphoric acid, HDHP, are the extractants of reference for the French DIAMEX–SANEX process for the separation of trivalent actinide ions from the lanthanide ions. In this work, the extraction of Eu³⁺ and Am³⁺ by the two extractants, alone or in mixtures, has been investigated under a variety of experimental conditions. The two cations are extracted by HDHP as the M(DHP · HDHP)₃ complexes with an Eu/Am separation factor of ～10. With DMDOHEMA, Eu³⁺ and Am³⁺ are extracted as the M(NO₃)₃(DMDOHEMA)₂ disolvate species with an Am/Eu separation factor of ～2. The metal distribution ratios measured with a mixture of the two reagents indicated that almost all lanthanides are extracted equally well. The extraction of Eu³⁺ and Am³⁺ by HDHP‐DMDOHEMA mixtures exhibits a change of extraction mechanism and a reversal of selectivity taking place at ～1 M HNO₃ in the aqueous phase. Below this aqueous acidity, HDHP dominates the metal extraction by the mixture, whereas DMDOHEMA is the predominant extractant at higher aqueous acidities. Some measurements indicated apparent modest antagonism between the two extractants in the extraction of Eu³⁺ and synergism in the extraction of Am³⁺. These data were interpreted as resulting from the formation in the organic phase of mixed HDHP‐DMDOHEMA species containing two HDHP and five DMDOHEMA molecules.     

Thermodynamic and Spectroscopic Studies on Am(III) and Eu(III) in the Extraction System of N,N,N',N'-Tetraoctyl-3-Oxapentane-1,5-Diamide in n-Dodecane/Nitric Acid

Abstract

Thermodynamic parameters (ΔG, ΔH, and ΔS) for the extraction of trivalent f-elements, M(III) (M = Am, Eu), with N,N,N',N'-tetraoctyl-3-oxapentane-1,5-diamide (TODGA) were determined in nitric acid/n-dodecane extraction system. The extraction of M(III) with TODGA was more exothermic than those with octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) and dihexyl-N,N-diethylcarbamoylmethyl phosphonate (DHDECMP). The difference in ΔH between the extractants was attributed to the difference in the binding mode between them, i.e. tridentate (TODGA) and bidentate (CMPO and DHDECMP). In addition, from the results of luminescence lifetime measurement, it was found that the inner-sphere of extracted Eu(III) was dehydrated completely, and occupied by TODGA and/or NO₃ ^?.     

SYNERGISTIC SELECTIVE EXTRACTION OF ACTINIDES(III) OVER LANTHANIDES FROM NITRIC ACID USING NEW AROMATIC DIORGANYLDITHIOPHOSPHINIC ACIDS AND NEUTRAL ORGANOPHOSPHORUS COMPOUNDS

ABSTRACT

New aromatic dithiophosphinic acids (R₂PSSH) with R = C₆H_5?, ClC₆H_4?, FC₆H_4? and CH₃C₆H_4? were synthesized, characterized and tested as potential separating agents for trivalent actinides over lanthanides. The extraction of Am(III), Eu(III) and other lanthanides was carried out from nitric acid medium with mixtures of R₂PSSHS and neutral organophosphorus compounds. There was no detectable extraction when R₂PSSHS were used alone as extractants for either Am(III) or Eu(III) (D_AM,EU.< 10^?3) under the experimental conditions used in this study. High separation factors (D_AM/D_EU > 20) with D_AM > 1 were achieved in the nitric acid range 0.1-1 mol/L by means of a synergistic mixture of bis(chloro-phenyl)dithiophosphinic acid + tributylphosphate (TBP), irioctylphosphine oxide (TOPO) or tributylphosphine oxide (TBPO). The high radiation resistance (up to 10⁶ Gy absorbed γ-doses) of the extractants was also demonstrated.     

Selective Separation of Scandium(III) and Yttrium(III) from other Rare Earth Elements using Cyanex302 as an Extractant

Abstract

Liquid‐liquid extraction and selective separation of scandium(III) and yttrium(III) with Cyanex302 (bis(2,4,4‐trimethylpentyl)monothiophosphinic acid) has been carried out by controlling the aqueous phase pH. Scandium(III) and yttrium(III) were completely recovered from the organic phase using 5.0 M and 4.0 M nitric acid respectively and determined spectrophotometrically as their complexes with Arsenazo(III). The influence of extractant concentration, equilibration time, nature of diluents, stripping agents, and diverse ions on the extraction of scandium(III) and yttrium(III) was investigated. The extractability of scandium(III), yttrium(III), and other rare earth elements was exploited for sequential separation of scandium(III)‐yttrium(III)‐lanthanum(III) and other rare earth elements viz. lanthanum(III), cerium(IV), praseodymium(III), neodymium(III), gadolinium(III), dysprosium(III), and ytterbium(III) in binary mixtures. The method presented is simple and rapid for isolation of scandium(III) and yttrium(III) from associated elements and has been successfully applied for their selective separation from complex matrices of USGS standard soil GXR‐2 and Japanese standard stream sediment sample Jsd‐3.     

Extraction Behavior of the Synergistic System 2,6‐ bis ‐(Benzoxazolyl)‐4‐ Dodecyloxylpyridine and 2‐Bromodecanoic Acid Using Am and Eu as Radioactive Tracers

Abstract

In this study, the extraction properties of a synergistic system consisting of 2,6‐bis‐(benzoxazolyl)‐4‐dodecyloxylpyridine (BODO) and 2‐bromodecanoic acid (HA) in tert‐butyl benzene (TBB) have been investigated as a function of ionic strength by varying the nitrate ion and perchlorate ion concentrations. The influence of the hydrogen ion concentration has also been investigated. Distribution ratios between 0.03–12 and 0.003–0.8 have been found for Am(III) and Eu(III), respectively, but there were no attempts to maximize these values. It has been shown that the distribution ratios decrease with increasing amounts of ClO₄ ^?, NO₃ ^?, and H⁺. The mechanisms, however, by which the decrease occurs, are different. In the case of increasing perchlorate ion concentration, the decrease in extraction is linear in a log–log plot of the distribution ratio vs. the ionic strength, while in the nitrate case the complexation between nitrate and Am or Eu increases at high nitrate ion concentrations and thereby decreases the distribution ratio in a non‐linear way. The decrease in extraction could be caused by changes in activity coefficients that can be explained with specific ion interaction theory (SIT); shielding of the metal ions, and by nitrate complexation with Am and Eu as competing mechanism at high ionic strengths. The separation factor between Am and Eu reaches a maximum at ～1 M nitrate ion concentration. Thereafter the values decrease with increasing nitrate ion concentrations.     

Synthesis of Pre‐Organized Bisdiglycolamides (BisDGA) and Study of their Extraction Properties for Actinides(III) and Lanthanides(III)

Bisdiglycolamides 1–9 were synthesized and studied as extracting agents for An(III) and Ln(III) from nitric acid solutions. Compounds 1d‐3 with rigid spacers as m‐xylylene and 6b‐9 with more flexible alkyl chain linkers, show higher selectivity for Eu(III) extraction over Am(III) than diglycolamides (TBDGA, DMDODGA, TODGA) in (50:50)_%Vol HPT/1‐octanol mixture. Am(III) and Eu(III) extraction kinetics are very fast and back‐extraction with more than 99% efficiency of both cations is possible after four times of contact of the loaded solvent with fresh 0.01 mol/L nitric acid solutions.     

Water Soluble PDCA Derivatives for Selective Ln(III)/An(III) and Am(III)/Cm(III) Separation

The synthesis and solvent extraction behavior of dipicolinic acid (pyridine-2,6-dicarboxylic acid, PDCA) and their derivatives have been studied for possible use in selective back-extraction of actinides, especially americium. The extraction was performed from an organic phase containing a mixture of trivalent actinides and lanthanides pre-extracted with N,N,N’,N’-tetraoctyl diglycolamide (TODGA). The efficiency of the back-extraction was enhanced when the picolinate platform was used in a heterocyclic decadentate ligand called h₄tpaen. Beyond selective An/Ln extraction, the aqueous soluble h₄tpaen ligand seemed a potential reagent for an intra-group Am(III)/Cm(III) separation with a separation factor SF_Cm/Am of about 3.5.     

Synthesis and Characterization of 6,6ˊ-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)-2,2ˊ-bipyridine (EH–BTzBP) for Actinide/Lanthanide Extraction and Separation

A new N-donor extractant, 6,6ˊ-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)-2,2ˊ-bipyridine (EH-BTzBP), was synthesized and tested for Am(III)/Ln(III) extraction and separation. EH-BTzBP in combination with 2-bromohexanoic acid (as lipophilic anion source) selectively extracts Am(III) from acidic solutions (HNO₃ ≤ 0.1M) with Am(III)/Eu(III) separation factors of about 70. Phase transfer kinetics is rapid, back-extraction of metal ions posed no issues, and there is no evidence of ligand degradation by acid hydrolysis or contact with hydrogen peroxide (which simulates some effects of radiolysis).     

Selective Extraction of Am(III) from PUREX Raffinate: The AmSel System

The separation of actinides(III) from used nuclear fuel is a key step for the recycling of used nuclear fuel in innovative fuel cycles. However, high neutron dose rates and heat load of short-lived curium isotopes complicate the production and handling of new nuclear fuel containing curium(III) and americium(III). Therefore, new processes have to be developed separating only americium(III) from PUREX (Plutonium-Uranium Recovery by Extraction) raffinate. This is achieved by coextracting An(III) and Ln(III) from PUREX raffinate using N,N,N’,N’-tetraoctyl-diglycolamide (TODGA), followed by the subsequent selective stripping of Am(III) by a water-soluble bis-triazinyl-bipyridin (sodium 3,3’,3’’,3’’’-([2,2’-bipyridine]-6,6’-diylbis(1,2,4-triazine-3,5,6-triyl))tetrabenzenesulfonate, SO₃-Ph-BTBP). The selectivity for Am(III) over Cm(III) is SF_{Cm(III)/Am(III)} ≈ 2.5, due to the inverse selectivity of TODGA and SO₃-Ph-BTBP. Additionally, a separation factor up to 1200 is achieved for the separation of Eu(III) from Am(III). The results demonstrate that the presented system works very well even at acidic conditions using nitric acid as the aqueous phase and does not require additional salting out agents.     

Studies on the Radiochemical Degradation of Tetraethylhexyl Diglycolamide and Ethylhexylphosphoric Acid in n-Dodecane Solution

The organic solvent phase composed of N,N,N’,N’-tetra-2-ethylhexyl diglycolamide (TEHDGA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) in n-dodecane (n-DD) is regarded as a promising candidate for single-cycle separation of americium (III) from high-level liquid waste. The radiochemical degradation of a solution of TEHDGA + HDEHP/n-DD was investigated by irradiating the solvent to various absorbed dose levels of γ-radiation. The neat extractants or a solution of extractants in n-dodecane were irradiated in the presence and absence of nitric acid. The degree of degradation was assessed by measuring the variation in the extraction behavior of Am(III), Eu(III) and other metal ions in irradiated solvent systems. The distribution ratio of americium and europium decreased with increase of absorbed dose. The presence of n-dodecane enhanced the radiolytic degradation of the solvent; however, the role of nitric acid during degradation was insignificant. The recovery of Am(III) and Eu(III) from the irradiated solvent system was studied. The recovery of Am(III) was quantitative in 3 contacts; however, the separation factor of Eu(III) over Am(III) during stripping decreased marginally with increase of absorbed dose.     

Extraction Behavior of Am(III) and Eu(III) from Nitric Acid Medium in Tetraoctyldiglycolamide-Bis(2-Ethylhexyl)Phosphoric Acid Solution

The extraction behavior of Am(III) and Eu(III) in a solution of tetra-octyldiglycolamide (TODGA), bis(2-ethylhexyl)phosphoric acid (HDEHP), and n-dodecane (n-DD) was studied to understand the role of TODGA and HDEHP in the combined solvent system. The extraction behavior of these metal ions was compared with those observed in TODGA/n-DD and HDEHP/n-DD. The effect of various parameters such as concentrations of HNO₃, TODGA, and HDEHP on the distribution ratio of Am(III) and Eu(III) was studied. Synergistic extraction of both the metal ions observed at lower acidities (<2.0 M) was attributed to the involvement of TODGA and HDEHP for extraction. However, the extraction of Am(III) and Eu(III) in the combined solvent was comparable with that observed in TODGA at higher acidities. The slope analysis of the extraction data confirmed the involvement of both the extractants at all acidities investigated in the present study.     

A New Method for Partitioning of Trivalent Actinides from High-Level Liquid Waste

The extraction behavior of Am(III) and Eu(III) in a solution of tetra-bis(2-ethylhexyl)diglycolamide (TEHDGA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) in n-dodecane (n-DD) was studied from nitric acid medium. The distribution ratio of Am(III) and Eu(III) in TEHDGA-HDEHP/n-DD was measured as a function of various parameters such as concentrations of nitric acid, TEHDGA, HDEHP, and nitrate ion. The data were compared with those obtained in individual solvents namely 0.1 M TEHDGA/n-DD and 0.25 M HDEHP/n-DD. The synergistic extraction of Am(III) and Eu(III) observed in a solution of 0.1 M TEHDGA – 0.25 M HDEHP/n-DD was attributed to the involvement of both TEHDGA and HDEHP for extraction. Slope analysis of the extraction data indicated the predominant participation of HDEHP for extraction at low acidities and TEHDGA and nitrate ion at higher acidity. The stripping behavior of Am(III) and Eu(III) from the extracted organic phase was investigated using citric acid (CA) and diethylenetriaminepentaacetic acid (DTPA). A suitable aqueous formulation was developed to separate Am(III) alone from chemically similar Eu(III) present in loaded organic phase, to facilitate a single-step separation of trivalent actinides from the high-level liquid waste (HLLW).     

Kinetics of Eu(III) extraction in macroporous bifunctional phosphinic acid resin

The rate of ion exchange of Eu(III) from semi-infinite bath containing dilute nitric acid solution was studied on a macroporous bifunctional phosphinic acid resin. The influence of particle size, concentration of nitric acid and temperature on the uptake of Eu(III) was examined. The kinetic data were fitted into the Reichenberg approximate solution, based on the Nernst–Planck resin diffusion model, that relates the fractional attainment of equilibrium (U_t) and internal diffusion coefficient (D_A). The measured D_A was of the order of 10^?13 m²/s, and it was found to increase with the increase of temperature, and decrease with the increase of particle size of the resin and concentration of nitric acid.