Use of organophosphorus extractants impregnated on silica gel for the extraction chromatographic separation of minor actinides from high level waste solutions

Silica-gel has been used as an inert support for the extraction chromatographic separation of actinides and lanthanides from HNO₃ and synthetic high level waste (HLW) solutions. Silica-gel was impregnated with tri-butyl phosphate (TBP), to yield STBP; 2-ethylhexyl phosphonic acid, mono 2-ethylhexyl ester (KSM-17, equivalent to PC-88A), SKSM; octyl(phenyl)-N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO), SCMPO; and trialkylphosphine oxide (Cyanex-923), SCYN and sorption of Pu(IV), Am(III) and Eu(III) from HNO₃ solutions was studied batchwise. Several parameters, like time of equilibration, HNO₃ and Pu(IV) concentrations were varied. The uptake of Pu(IV) from 3.0M HNO₃ followed the order SCMPO>SCYN>SKSM>STBP. With increasing HNO₃ concentration, D _Pu increased up to 3.0M of HNO₃ for STBP, SKSM and SCMPO and then decreased. In the case of Am and Eu with SCMPO, the D values initially increased between 0.5 to 1.0M of HNO₃, remained constant up to 5.0M and then slightly decreased at 7.5M. Also, the effects of NaNO₃, Nd(III) and U(VI) concentrations on the uptake of Am(III) from HNO₃ solutions were evaluated. With increasing NaNO₃ concentration up to 3.0M, D _Am remained almost constant while it was observed that it decreases drastically by adding Nd(III) or U(VI). The uptake of Pu and Am from synthetic pressurized heavy water reactor high level waste (PHWR-HLW) in presence of high concentrations of uranium and after depleting the uranium content, and finally extraction chromatographic column separation of Pu and Am from U-depleted synthetic PHWR-HLW have been carried out. Using SCMPO, high sorption of Pu, Am and U was obtained from the U-depleted HLW solution. These metal ions were subsequently eluted using various reagents. The sorption results of the metal ions on silica-gel impregnated with several phosphorus based extractants have been compared. The uptake of Am, Pu and rare earths by SCMPO has been compared with those where CMPO was sorbed on Chromosorb-102, Amberchrom CG-71 and styrene divinylbenzene copolymer immobilized in porous silica particles.     

Characterization of high level waste for minor actinides by chemical separation and alpha spectrometry

The high level waste (HLW) generated from the reprocessing of the spent fuel of pressurized heavy water reactor has been characterized for the minor actinides. The radiation dose of the waste solution was reduced by radiochemical separation of cesium from HLW by solvent extraction with chlorinated cobalt dicarbollide dissolved in 20% nitrobenzene in xylene. Minor actinides (Np, Pu, Am, Cm) in the high level waste were assayed by alpha spectrometry following radiochemical separation. The gross alpha activity determined by liquid scintillation agrees well (within 10%) with the cumulative quantities of actinides determined by alpha spectrometry.     

Reversed-phase partition chromatographic separation of minor actinides with bis(2-ethylhexyl) sulfoxide from acidic nitrate PUREX waste solutions

The uptake behavior of U(VI), Pu(IV), Am(III) and a few long-lived fission products from nitric acid media by bis(2-ethylhexyl) sulfoxide (BESO) adsorbed on Chromosorb has been studied U(VI), Pu(IV) and Zr(IV) are taken up appreciably as compared to trivalent actinides/lanthanides including some coexisting fission product contaminants which are weakly sorbed on the column. Chromosorb could be loaded with (1.12±0.03) g of BESO per g of the support. Maximum sorption is observed around 4–5 mol·dm^–3 HNO₃ for both U(VI) and Pu(IV), which are sorbed as their disolvates. The elution of (U(VI) and Pu(IV) from the metal loaded sorbent has also been optimized. Desorption of U(VI) is easily accomplished with dilute nitric acid (ca. 0.01 mol·dm^–3)while Pu(IV) is reductively stripped with 0.1 mol·dm^–3 NH₂OH·HCl. Effective sequential separation of U(VI), Pu(IV) and Am(III) from their several admixtures could be readily achieved from real medium and low level active acidic process raffinates.     

Rapid sequential separation of actinides using Eichrom's extraction chromatographic material

The presence of ²²⁶ Ra in an estuary formerly affected by direct discharges of waste from a phosphate fertilizer complex has been investigated. Specific activities ranging from 3.6 to 45.2 mBq/l have been detected. In general, activity levels are lower than those detected when direct discharges were carried out. However, there is still a clear contamination due to the disposal of phosphogypsum in open air piles by the river. Moreover, it seems that ²²⁶ Ra is being redissolved from the contaminated bed sediments, which also contributes to an enhancement in the activity levels of the estuary waters.     

A rapid sequential separation of actinides using Eichrom's extraction chromatographic material

For the past 10 years, Eichrom has provided a variety of innovative products for faster separation of radionuclides to radioanalytical laboratories. However, recently, environmental testing laboratories have been challenged to generate reliable data more quickly. To assist our customers with rapid separations, Eichrom has developed a new configuration for its existing extraction chromatographic material that operates with vacuum assisted flow. After pre-concentration of actinides from a given sample, the actinides are dissolved in a suitable solution. Appropriate Eichrom Resin Cartridges are placed on a vacuum box system. Sample solutions are then passed through the cartridges under optimal vacuum pressure. In this paper, a scheme for separation of actinides in different matrices are discussed using Eichrom Resin Cartridges. Time required for separations, test results and ease of use are the primary discussions of this paper.     

Recovery of actinides from acidic waste solutions generated in research facilities using adsorption and extraction techniques

Journal of Radioanalytical and Nuclear Chemistry - In the present study various separation methods were investigated for the recovery of actinides from aqueous waste solutions. Extraction behavior...     

Recovery of actinides extracted by Truex solvent from high level waste using complexing agents

The sorption and migration of radiostrontium in a calcareous soil from Yu Zhong county of Gansu province (China) was studied using batch and column experiments. Sorption isotherms, breakthrough curves and concentration profiles for the untreated soil and the soil treated to remove CaCO₃ were determined, respectively. It was found that radiostrontium is a relatively mobile nuclide in calcareous soil and removal of CaCO₃ from the soil slightly increases the retention ability for radiostrontium. The breakthrough curves were fitted to the analytical solution of a one-dimensional convection-dispersion transport model that assumes a reversible linear isotherm. Good agreement was obtained between the measured and predicted concentration profiles.     

Recovery of actinides extracted by Truex solvent from high level waste using complexing agents

This work deals with the batch studies on stripping of actinides extracted by a mixture octyl(phenyl)-N,N-diisobutyl-carbamoylmethylphosphine oxide (CMPO) and tri-n-butyl phosphate (TBP) in n-dodecane (Truex solvent) from simulated high level waste (HLW) solution. The stripping of americium and plutonium from acid-bearing CMPO-TBP mixture is carried out using a mixture of weak acid, weak base and complexing agent as strippant. A mixture of formic acid, hydrazine hydrate and citric acid appeared to be best suited for efficient stripping of americium and plutonium. With appropriate modifications in the concentration of individual constitutents, this strippant can be used for the recovery of actinides from loaded Truex solvent with any acid content.     

Recovery of neptunium from highly radioactive waste solutions of PUREX origin using CMPO

The partitioning and recovery of²³⁷Np from three types of simulated high level waste solutions originating from PUREX processing of spent nuclear fuels such as sulfate bearing high level waste (SB-HLW), HLW from a pressurised heavy water reactor (PHWR-HLW) and from a fast breeder reactor (FBR-HLW) have been carried out using a mixture of 0.2M CMPO and 1.2M TBP in dodecane. Quantitative extraction of neptunium was possible by either oxidizing it to the hexavalent state keeping K₂Cr₂O₇ at 0.01M concentration or by reducing it to tetravalent state keeping Fe²⁺ at 0.02M concentration. Stripping of neptunium was carried out using different reagents, such as dilute nitric acid, oxalic acid and sodium carbonate. Almost quantitative recovery of neptunium has been achieved during these studies.     

Extraction chromatographic method for the separation of actinides and lanthanides using EDHBA grafted AXAD-16 polymer

A new extraction chromatographic method has been developed by grafting chloromethylated polymer support with 4-ethoxy-N,N-dihexylbutanamide (EDHBA), for the selective extraction of U(VI), Th(IV), La(III) and Nd(III) from highly acidic matrices. The developed grafted polymer has been characterized using ¹³C-CPMAS NMR spectroscopy, FT-NIR spectroscopy and also by CHN elemental analysis. The water regaining capacity of the grafted polymer is studied by TGA measurements and the active participation of the amide moiety towards metal ion complexation has been confirmed by Far IR spectroscopy. For the quantitative extraction of metal ions to the resin phase, various physio-chemical parameters are optimized by both static and dynamic methods. The developed amide grafted polymeric matrix shows good distribution ratio values even at high acidities, with the maximum metal sorption capacity values being 0.36, 0.69, 0.32 and 0.42 mmol g⁻¹ for U(VI), Th(IV), La(III) and Nd(III), respectively, at 6 M HNO₃ medium. The kinetics of metal ion phase equilibration is found to be moderately fast, with t_1/2 values of <6 min, for all the analytes of interest. The limits of analyte quantification (LOQ) using the developed method are in the range of 15-30 μg L⁻¹. Moreover, the sequential separation of the sorbed actinides and lanthanides could be achieved by first eluting with 100 mL of distilled water (for actinides) followed by elution with 20 mL of 0.1 M EDTA (for lanthanides). The selectivity behavior and the practical applicability of the developed resin are tested using synthetic low level nuclear reprocessing mixtures and also with monazite sand. The analytical data are within 3.8% relative standard deviation, reflecting the reproducibility and reliability of the developed method.     

高放废液中分离回收镧系-锕系元素萃取剂的研究进展

概述了近十几年来国内外有关用于高放废液镧系-锕系元素萃取分离中新萃取剂的研究进展,并对酰胺类、硫代磷类、硫代吡唑啉酮类等新萃取剂的设计筛选等进行了讨论。     

Use of actinides in uncommon oxidation states for their extraction and separation from alkaline solutions

The extraction behavior of Am(IV–VI) from high pH solutions in the presence of carbonates, pyrophosphates or polyphosphates of alkali metals and of Np(VI–VII) from alkaline solutions with acylpyrazolones (1-phenyl-3-methyl-4-benzoylpyrazolone-5, PMBP) and extractants of the phenol type [bis(2-oxy-4-alkyl-benzoil)amin, CAAF] has been studied. The extraction ability of phenolic extractants with respects to Np(VII) is determined generally by its state in the alkaline solution. Maximum extraction is observed when Np(VII) is present as hydroxo complex and minimum extraction, when the solution contains oxo-ions. During the extraction the reduction of Np(VII) to Np(VI) is possible. Hexavalent neptunium can be extracted by phenol extractants too, but more slowly and with smaller distribution coefficients in comparison with Np(VII). The stabilization of transplutonium elements (TPE) in the highest oxidation states in alkaline solutions contaning carbonate and pyrophosphate ions, in combination with extraction by PMBP and CAAF, allows to realize the separation of transplutonium elements which are very similar in their properties. Methods of separation for americium and curium have been developed. They are based on the ability of trivalent curium to be extracted quantitatively from 0.1M sodium pyrophosphate solution (pH 10) and 1.0M potassium carbonate solution (ph 13.4) by PMBP in chloroform and by CAAF in carbon tetrachloride, respectively, with high distribution coefficients, whereas americium which is electrochemically oxidized to Am(VI) in these media, remains in the aqueous phase, since it reduces only to Am(V) when contacting the extractant. The separation factor of the couple Cm(III) Am(VI) is about 10³.     

Selective separation of minor actinides and lanthanides using aromatic dithiophosphinic and phosphinic acid derivatives

A new extractant for the separation of actinide(III) and lanthanide(III) cations, bis(o-trifluoromethylphenyl) phosphinic acid (2) was synthesized. The synthetic route employed mirrors one that was employed to produce the sulfur containing analog bis(o-trifluoromethylphenyl) dithiophosphinic acid (1). Classic radiochemical methods and absorbance spectroscopy were used to study the coordination chemistry of the Am-dithiophosphinic acid and Am-phosphinic acid complexes.     

Characterization of high level nuclear waste solutions from different origin

Journal of Radioanalytical and Nuclear Chemistry - A simple, simultaneously multi-elemental, ICP-AES based method was optimized to characterize nuclear high level waste solutions from different...     

Extraction of uranium and plutonium from oxalate bearing solutions using phosphonic acid: Solvent extraction, extraction chromatography and infrared studies

Solvent extraction and extraction chromatography studies of uranium and plutonium from oxalate supernatant solutions were carried out using 2-ethyl hexyl-2-ethyl hexyl phosphonic acid (PC88A). Based on the distribution data, it was inferred that both the uranium and plutonium could be recovered satisfactorily from such a solution. These studies were found to be useful in optimising the appropriate concentration of PC88A, HNO₃, oxalic acid and temperature to recover more than 90% of plutonium from the large volumes of oxalate bearing waste solutions. Spectral characteristics of the extractant and its complexing behavior with U(VI) was also studied using IR & FTIR.     

Scaling-up experience of actinides partitioning from intermediate level high salted alkaline waste streams of Purex process using Versatic-10 extractant

Partitioning of minor alpha-emitting actinides, especially U, Pu and Am from medium active alkaline waste is possible from intermediate level liquid wastes (ILLW) produced during spent fuel reprocessing following Purex process. This paper deals with the efficient removal of alpha-activity from ILLW by solvent extraction process. Counter current batch extraction with O/A ratio 2:1 as well as multistage mixer settler has demonstrated that most of the alpha-activity was removed from the alkaline effluents using 20% Versatic-10 (V-10) in dodecane after giving 3 to 4 contacts, thus converting alkaline waste as non-alpha waste. Under the optimum conditions (pH 9.0-9.5 and VA-10), both Pu(IV) and Am(III) are highly extractable whereas U(VI) is relatively poorly extracted. To assess the applicability of this process for regular treatment of the waste, a feasibility study on pilot plant scale using six stage mixer settler was operated to treat the ILLW. The results indicated that almost >99.90% alpha-emitting actinides are removed. Dilute nitric acid (0.5M HNO₃) served as the most efficient strippant for all these actinides. This facilitate an easy regeneration of the extractant which can be recycled. This method is useful in obtaining alpha-free wastes and had positive impact on ease and safety aspects during subsequent waste treatment and long term storage.     

Extraction of actinides and fission products from salt solutions using polyethylene glycols (PEGs)

The extraction behavior of several metal ions viz., Am³⁺, Eu³⁺, UO₂ ²⁺, Th⁴⁺, Sr²⁺ and Cs⁺ was investigated from sulphate medium employing phosphotungstic acid (PTA) and polyethylene glycol (PEG). The influence of various parameters such as pH, PTA concentration, PEG concentration and salt concentration was studied. The order of extraction followed the trend: Am³⁺>Eu³⁺>>Th⁴⁺>UO₂ ²⁺>Sr²⁺>Cs⁺ which deviate significantly from the reported order with conventional solvents. The relatively poor extraction of UO₂ ²⁺, Sr²⁺ and Cs⁺ was ascribed to their lack of interaction with the phosphotungstate anion. The separation behaviour of Am³⁺ vis-a-vis Eu³⁺ was also investigated under different experimental conditions.     

Adamantylcalixarenes with CMPO groups at the wide rim: synthesis and extraction of lanthanides and actinides

Starting from p-adamantylcalix[4]- and [6]arenes functionalized with carboxylic acid or ester groups at the adamantane nuclei, carbamoylmethylphosphine oxide (CMPO)-containing ligands of a novel type were synthesized. They were studied as extractants for a series of f-block elements including radioactive ¹⁵²Eu(III), ²⁴¹Am(III), ²³³U(VI), and ²³⁹Pu(IV). Tetrameric ligand 4b in which CMPO residues are connected to adamantane nuclei through methylene groups gave the best extraction results for lanthanides and actinides. For all the ligands the extraction efficiency does not decrease at higher nitric acid concentration. Although the discrimination between trivalent actinides and lanthanides is not good, all ligands are highly selective for thorium(IV) with the best separation factor achieved in the case of hexameric ligand 5 (D_Th/D_Ln>24).     

Narrow rim CMPO/adamantylcalix[4]arenes for the extraction of lanthanides and actinides

Six p-(1-adamantyl)calix[4]arenes 7, 8 with four differently attached diphenyl-carbamoylmethylphosphine oxide (CMPO) functions at the narrow rim were synthesized. This series was extended by adamantylcalix[4]arenes with two CMPO and two ester, acid or (diethylphosphono)acetylamino groups. Structures of new compounds were proved by NMR, mass-spectrometry and a single-crystal X-ray analysis for the intermediate di-phthalimide 10₃. The extraction studies towards selected lanthanides and thorium showed that the ligands 7 surpassed the corresponding p-H, p-tert-butyl and p-tert-octyl analogues 3-5 in lanthanide extraction while thorium was extracted with the same or lesser extent. For the lanthanide extraction D_Ln(7₄)>D_Ln(7₃)≈D_Ln(7₂), which follows the order established earlier for ligands 3-5. Among the tetra-CMPO derivatives of type 8, the ligand 8_3/4 was the best extractant for which the D_Ln and D_Th values were comparable with those for 7₄.     

Reversed phase extraction chromatographic separation of thorium with Amberlite LA-1 from malonate solutions

Thorium was extracted at pH 5.0 from 0.01 M malonic acid on a column of silica gel coated with Amberlite LA-1. Thorium was separated from alkali and alkaline earths, managenese, iron, cobalt, nickel, zinc, tin, in binary mixtures by taking advantage of the difference in the pH of formation of malonato complexes. Thorium was separated from zirconium, uranium, scandium, molybdenum, titanium, by exploiting the difference in the stability of malonato complexes. The method was extended for the analysis of thorium in monazite.