Transport of lanthanides and fission products through supported liquid membranes containing N,N,N′,N′-tetraoctyl diglycolamide (TODGA) as the carrier

Facilitated transport of trivalent lanthanides, viz. La(III), Eu(III), Lu(III) and several fission product elements such as Tc, Mo, Zr, Pd, I, Cs and Ru across a flat sheet supported liquid membrane made of PTFE impregnated with N,N,N′,N′-tetraoctyl diglycolamide (TODGA) in n-dodecane was investigated from dilute nitric acid solutions. The transport rates of lanthanides increased with nitric acid concentration in a manner similar to their distribution ratios. The trend in metal ion transport after 75 min followed the order: La > Eu > Lu > Zr > Sr > I > Pd ~ Tc > Ru > Mo ~ Cs, which was consistent even after 5 h of operation. However, the transport of I reached the maximum value of ~26% in 100 min and remained constant thereafter. In the case of Am(III) transport studies, excellent decontamination from Zr was achieved when 0.4 M oxalic acid was added to the feed solution.     

Studies on the Use of N,N,N´,N´-Tetra(2-ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning. I: Investigation on Third-Phase Formation and Extraction Behavior

Abstract

Diglycolamides have emerged as an interesting class of extractants for actinide partitioning from high-level waste (HLW). N,N,N´,N´-tetraoctyl diglycolamide (TODGA) has been extensively studied for lanthanide-actinide co-extraction behavior. The present work deals with a branched isomer of TODGA, that is, N,N,N´,N´-tetra(2-ethylhexyl) diglycolamide (TEHDGA). TEHDGA was studied for the extraction of ²⁴¹Am and third-phase formation. The effect of using different phase modifiers on the prevention of the formation of a third phase during nitric acid extraction by TEHDGA along with the acid uptake behavior by TEHDGA in the presence of the modifiers was studied. The modifiers used for this purpose were di(n-hexyl)octanamide (DHOA), isodecanol, and n-decanol. The effect of the modifiers on the uptake of ²⁴¹Am as a function of acid concentration and as a function of modifier concentration was also examined. DHOA was found to be a suitable modifier, in spite of its high acid uptake. The uptake of lanthanides Ce, La, Eu, Gd, and Nd and elements such as Fe, Ni, Mn, Mo, Ru, Sr, and Cs with DHOA-modified TEHDGA–n-dodecane solvent systems were investigated. The results obtained indicated that, while DHOA-modified TEHDGA/n-dodecane extracted lanthanides and actinides, it did not show any significant uptake of other elements. Thus, the TEHDGA-DHOA/n-dodecane solvent system can be used effectively for the partitioning of lanthanides and actinides from HLW.     

Extraction of Trivalent Rare Earths and Minor Actinides from Nitric Acid with N,N,N’,N’-Tetradodecyldiglycolamide (TDdDGA) by Using Mixer-Settler Extractors in a Hot Cell

Single-stage batch experiments to reveal the extraction properties of N,N,N’,N’-tetradodecyldiglycolamide (TDdDGA) for Y, La, Eu, Nd, and Am in nitric acid were carried out. The distribution ratios of Y, Eu, Nd, and Am exceeded 10 when the nitric acid concentration was 1–2 mol/dm³ (M), and the distribution ratio of La was 5.5 when the nitric acid concentration was 2 M. A continuous counter-current experiment using 0.1 M TDdDGA diluted with n-dodecane was performed using mixer-settler extractors installed in a hot cell. Nitric acid with a concentration of 2.1 M containing minor actinides (MAs: Am and Cm), rare earths (REs: Y, La, Nd, and Eu), and other fission products (Sr, Cs, Zr, Mo, Ru, Rh, and Pd) was fed to the extractor. TDdDGA effectively extracted MAs and REs from the feed, while other fission products were barely extracted. The extracted MAs and REs were back-extracted by bringing them in contact with 0.02 M nitric acid, and they were collected as the MA–RE fraction. The results indicated that more than 98% of Am and Cm in the feed were recovered in the MA–RE fraction. The proportions of Y, La, Nd, and Eu in the MA–RE fraction were 94.0%, 99.9%, 99.9%, and 86.9%, respectively.     

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

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

Direct Selective Extraction of Actinides (III) from PUREX Raffinate using a Mixture of CyMe4BTBP and TODGA as 1-cycle SANEX Solvent

Abstract

Within the framework of our research activities related to the partitioning of spent nuclear-fuel solutions, the direct selective extraction of trivalent actinides from a simulated PUREX raffinate was studied using a mixture of CyMe₄BTBP and TODGA (1-cycle SANEX). The solvent showed a high selectivity for trivalent actinides with a high lanthanide separation factor. However, the coextraction of some fission product elements (Cu, Ni, Zr, Mo, Pd, Ag, and Cd) from a simulated PUREX raffinate was observed, with distribution ratios up to 30 (Cu). The extraction of Zr and Mo could be suppressed using oxalic acid but the use of the well-known Pd complexant N-(2-Hydroxyethyl)-ethylendiamin-N,N′,N′-triacetic acid (HEDTA) was unsuccessful. During screening experiments with different amino acids and derivatives, the sulfur-bearing amino acid L-Cysteine showed good complexation of Pd and prevented its extraction into the organic phase without influencing the extraction of the trivalent actinides Am (III) and Cm (III). The optimization studies included the influence of the L-Cysteine and HNO₃ concentration and the kinetics of the extraction. The development of a process-like extraction series showed very promising results in view of further optimizing the process. A strategy for a single-cycle process is proposed within this article.     

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.     

Radiolytic Stability of N,N,N′,N′-Tetraoctyl Diglycolamide (TODGA) in the Presence of Phase Modifiers Dissolved in n-Dodecane

The radiolytic stability of a promising extractant for actinide partitioning from high-level radioactive liquid waste, namely N,N,N',N'-tetraoctyl diglycolamide (TODGA) was investigated in the presence of several phase modifiers, viz. N,N-dihexyloctanamide (DHOA), tri-n-butyl phosphate (TBP), 1-decanol, and iso-decanol dissolved in n-dodecane. The distribution ratio of Am(III) decreased with increased radiation dose studied up to 1000 kGy. Nevertheless, all the compositions of extractants showed fairly high extraction of Am(III) up to 500 kGy (D_Am: ≥ 50), beyond which significant decrease was observed. However, the D_Am values were sufficiently high for process applications for the chosen compositions even at an absorbed dose of 1000 kGy. The stripping behavior of Am(III) with 0.2 M HNO₃ was found to be favorable with increased absorbed dose by the solvent up to 1000 kGy. With an increased absorbed dose, the loading of Nd(III) in the organic phase decreased due to depletion of ligand/extractant concentration (TODGA) in the organic phase. There was marginal variation in the hydrodynamic parameters such as density, viscosity, and interfacial tension (IFT) of the irradiated solvents vis-a-vis fresh/unirradiated solvent.     

Demonstration of a TODGA‐Based Continuous Counter‐Current Extraction Process for the Partitioning of Actinides from a Simulated PUREX Raffinate,Part II: Centrifugal Contactor Runs

Abstract

The efficiency of the partitioning of trivalent actinides from a PUREX raffinate is demonstrated with a TODGA+TBP extractant mixture dissolved in an industrial aliphatic solvent TPH. Based on the results of cold and hot batch extraction studies and with the aid of computer code calculations, a continuous counter‐current process is developed and two flowsheets are tested using miniature centrifugal contactors. The feed solution used is a synthetic PUREX raffinate, spiked with ²⁴¹Am, ²⁴⁴Cm, ²⁵²Cf, ¹⁵²Eu, and ¹³⁴Cs. More than 99.9% of the trivalent actinides and lanthanides are extracted and back‐extracted and very high decontamination factors are obtained for most fission products. The co‐extraction of zirconium, molybdenum, and palladium is prevented using oxalic acid and HEDTA. However, 10% of ruthenium is extracted and only 3% is back‐extracted using diluted nitric acid. The experimental steady‐state concentration profiles of important solutes are determined and compared with model calculations and good agreement is generally obtained.     

Development of a TODGA based Process for Partitioning of Actinides from a PUREX Raffinate Part I: Batch Extraction Optimization Studies and Stability Tests

Abstract

The extractant, N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) has been evaluated for the separation of actinides(III) and lanthanides(III) from a high active raffinate (HAR). The effect of oxalic acid and HEDTA complexant on the extraction of actinides(III), lanthanides(III), and important fission products (e.g. Mo, Pd, Sr, Zr, Ru etc.) from synthetic HAR has been studied with 0.2 mol/L TODGA in TPH. With an extractant mixture of TODGA and tributyl phosphate (TBP) the amount of oxalic acid can be reduced to less than 0.3 mol/L for the effective complexation of zirconium, whereas the distribution ratios of actinides(III) and lanthanides(III) are still high for the separation from HAR. Furthermore the maximum loading of lanthanides (e.g. Nd) can be significantly increased by adding TBP to the extractant. However, the extraction of oxalic acid and nitric acid also increased by the addition of TBP, which can lead to problems during back extraction of the loaded extractant. Extraction studies after radiolysis and hydrolysis reveal that the TODGA+TBP mixture is a sufficient stable extraction system suited for further process development studies.     

Selective Removal of Uranium from High‐Level Waste Solution Employing Tri‐n‐Butyl Phosphate as the Extractant

Abstract

Conditions for the selective removal of uranium from high‐level waste solution have been optimized using tri‐n‐butyl phosphate (TBP) as the extractant. Various aqueous soluble reducing agents viz. hydroxylamine nitrate (HAN), hydrazine nitrate (HN), and diethyl hydroxylamine nitrate (DEHAN) as well as n‐dodecane soluble reductant viz. tert‐butyl hydroquinone (TBH) have been evaluated for the separation of U with respect to Pu and Np. The combination of DEHAN and TBH has been found to be most promising for the selective extraction of U from HLW. Extraction data of a few other metal ions expected to be present in high‐level waste solutions viz. Am(III), Eu(III), Zr(IV), Sr(II), and Cs(I) are also obtained.     

Demonstration of a TODGA based Extraction Process for the Partitioning of Minor Actinides from a PUREX Raffinate

Abstract: Efficient recovery of minor actinides (MA) from genuine PUREX raffinate has been successfully demonstrated by the TODGA + TBP extractant mixture dissolved in an industrial aliphatic solvent TPH. The process was carried out in centrifugal contactors using an optimized flow‐sheet involving a total of 32 stages, divided into 4 stages for extraction, 12 stages for scrubbing and 16 stages for back‐extraction. Very high feed decontamination factors were obtained (Am, Cm ～ 40 000) and the recovery of these elements was higher than 99.99%. Of the non‐lanthanide fission products only Y and a small part of Ru were co‐separated into the product fraction together with the lanthanides and the MA.     

EXTRACTION OF Am FROM NITRIC ACID BY CARBAMOYL-PHOSPHORYL EXTRACTANTS: THE INFLUENCE OF SUBSTITUENTS ON THE SELECTIVITY OF Am OVER Fe AND SELECTED FISSION PRODUCTS

A number of neutral extractants containing the P(0)(CH₂)_nC(0)N raolety were evaluated for their ability to extract Am from nitric acid and their selectivity for Am over Fe and selected fission products. Extractants containing alkoxy, alkyl, and aryl substltuents were evaluated. Tetrachloroethylene was used as a diluent. Fission products selected for study were Y, Zr, Mo, Tc, Ru, Rh, Pd, La, Ce, Pr, Nd, Sra, and Eu. The conclusions drawn were that the most efficient and selective Am extractant contains a single carbon bridging group, one or two phenyl groups attached to the phosphorus atom and l9obutyl groups attached to the amide nitrogen.     

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.     

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 ^?.     

Adsorption of Some Typical Fission Products onto a Novel Macroporous Silica-based Dialkyl Derivative of Pyridine Impregnated Material

A macroporous silica-based multidentate soft-ligand 2,6-bis(5,6-di(iso-hexyl)-1,2,4-triazine-3-yl)pyridine (BDIHTP) material, BDIHTP/SiO₂-P, was synthesized by impregnating and immobilizating BDIHTP into the pores of the SiO₂-P particles. The adsorption behavior of some typical fission products Mo(VI), Zr(IV), Ru(III), Pd(II), Rh(III), and a part of rare earths La(III), Ce(III), Nd(III), Eu(III), Gd(III), Dy(III), Er(III), Yb(III), and Y(III) contained in highly active liquid waste (HLW) onto BDIHTP/SiO₂-P was investigated. The effects of contact time and the concentration of HNO₃ in the range of 0.3 M to 5.0 M were examined. The BDIHTP/SiO₂-P materials showed excellent adsorption ability and high selectivity for Pd(II) greater than all of the tested metals. It was contributed to the effective complexation of Pd(II), a soft-Lewis acid and an electron-pair acceptor, with BDIHTP, a soft-Lewis base and an electron-pair donor. The chromatographic partitioning of the tested metals from 1.0 M HNO₃ by BDIHTP/SiO₂-P packed column was performed. Pd(II) was effectively eluted with 0.2 M thiourea-0.1 M HNO₃ and then separated from the others. The results are beneficial to partitioning of the long-lived minor actinides and Pd(II) together from HLW by the BDIHTP/SiO₂-P materials.     

Demonstration of an Improved Total Partitioning Process for High Level Liquid Waste Using Annular Centrifugal Contactors

High level liquid waste (HLLW) produced from the reprocessing of the spent nuclear fuel still contains moderate amounts of uranium, transuranium (TRU) actinides, ⁹⁰Sr, ¹³⁷Cs, etc., and thus constitutes a permanent hazard to the environment. The partitioning and transmutation (P&T) strategy has increasingly attracted interest for the safe treatment and disposal of HLLW, in which the partitioning of HLLW is one of the critical technical issues. An improved total partitioning process, including a TRPO (tri-alkylphosphine oxide) process for the removal of actinides, a CESE (crown ether strontium extraction) process for the removal of Sr, and a calixcrown ether extraction process for the removal of Cs, has been developed to treat Chinese HLLW at the Institute of Nuclear and New Energy Technology (INET), Tsinghua University, China. A demonstration test of the improved total partitioning process was carried out using 74-stage 10-mm-dia annular centrifugal contactors and simulated HLLW. The test results showed that the decontamination factors were >1.2 × 10⁶, 4600, and 7500 for Nd, Sr, and Cs, respectively. In the test, Nd was used to simulate Am. During the test, 74-stage 10-mm-dia annular centrifugal contactors worked stable continuously with no stage failing or interruption of the operation.     

Solvent Extraction of Plutonium(IV), Uranium(VI), and Some Fission Products with Di-n-octylsulfoxide

Abstract

Extraction behavior of plutonium(IV), uranium(VI), and some fission products from aqueous nitric acid media with di-n-octylsulfoxide (DOSO) has been studied over a wide range of conditions. Both the actinides are extracted essentially completely, whereas fission product contaminants like Zr, Ru, Ce, Eu, and Sr show negligible extraction. The absorption spectra of sulfoxide extracts containing either Pu⁴⁺ or UO₂ ²⁺ indicate the species extracted from nitric acid into the organic phase to be Pu(NO₃)₄. 2DOSO and UO₂(NO₃)₂. 2DOSO, respectively. Extraction of these actinides decreases with increasing temperature, indicating the extraction to be exothermic. DOSO extracts plutonium and uranium better than di-n-hexylsulfoxide (DHSO) under all condition and is also more soluble in aromatic diluents than the latter. The effect of gamma radiation on the extraction properties of DOSO is found to be similar to that of DHSO.     

Supercritical Fluid Dissolution and Extraction of Trivalent Metal Cations from Different Matrices

Studies on the recovery of trivalent metal ions such as Nd³⁺Eu³⁺ (taken as homologs of Am(III)) from solid oxide (Nd₂O₃), Thorium concentrate (obtained from Monazite ore processing), tissue paper/surgical gloves (rubber), and plant samples have been carried out by supercritical fluid extraction (SFE) using supercritical CO₂ and ethanol/nitric acid. N,N,N’,N’-tetraoctyl diglycolamide (TODGA) was used as the extractant in these studies. The results showed that the recovery of Nd increased with TODGA concentration from 50% (no TODGA) to 70% (10% TODGA) at 3 M HNO₃ in ethanol. However, the extraction of Nd at 1 M HNO₃ was invariant with 1-3% (v/v) TODGA concentration (73 ± 4%). Interestingly, REEs recovery from Th concentrate was ? 60% even without TODGA using ethanol/3 M HNO₃ mixture. On the other hand, quantitative recovery of ^152,154Eu from tissue paper and surgical gloves sample could be achieved using 3 M HNO₃/ethanol mixture. This suggested that it would be possible to decontaminate the contaminated laboratory waste papers using SFE technique.     

Liquid-Liquid Extraction of Ruthenium from Chloride Media by N,N'-Dimethyl- N,N'-Dicyclohexylmalonamide

Abstract

Research on the solvent extraction of ruthenium from hydrochloric acid media has been carried out using N,N'-dimethyl-N,N'-dicyclohexylmalonamide (DMDCHMA) dissolved in 1,2-dichloroethane. Ruthenium extraction percentages (%E) ranging from 50% to 80% have been achieved for HCl concentrations between 5 M and 7 M. Extraction curves exhibiting the dependence of the %E ruthenium on HCl concentration in the aqueous phases are presented, the latter solutions being obtained by dissolution of either Ru(III) or Ru(IV) salts. The influence of some experimental parameters on the %E Ru, such as the equilibration time, extractant concentrations, and hydrogen-ion activities, has been thoroughly investigated. Additionally, DMDCHMA is also adequate for extracting Pd(II) from 5 M to 7 M HCl solutions and under similar experimental conditions, %E Rh(III) is below 5%, and Pt(IV), Ir(III), and Ir(IV) cause the formation of third phases. Both Ru and Pd(II) can be successfully stripped from the loaded organic phases with water. A partition scheme to isolate Ru from a number of some associated elements has also been attempted.     

Modified Diglycolamides for the An(III) + Ln(III) Co-separation: Evaluation by Solvent Extraction and Time-Resolved Laser Fluorescence Spectroscopy

The use of two recently developed diglycolamide-based extractants for the co-separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is described and compared to the well-known extractant TODGA (N,N,N’,N’-tetraoctyl diglycolamide). The addition of one or two methyl groups to the central methylene carbon atoms of the TODGA molecule leads to a reduction of the extraction efficiency for An(III) and Ln(III). This is attributed to a lower complex formation constant, which was proven by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS). Conditional stability constants were determined by solvent extraction and TRLFS. The reduction in extraction efficiency leads to overall reduced distribution ratios of all tested metal ions, including Sr(II). The reduced Sr(II) extraction is beneficial as a co-extraction in a solvent extraction process could be avoided, while an efficient extraction of the desired An(III) and Ln(III) is still achieved. Furthermore, this might be a benefit, as the stripping behavior might be improved, even at moderate nitric acid concentrations. The slightly higher affinity of the diglycolamides towards Eu(III) over Am(III) is represented by all ligands, although the selectivity is rather low. This results in promising extraction properties of the modified diglycolamides towards the development of continuous solvent extraction processes.