Bis(2-ethylhexyl)sulfoxide as an extractant for americium(III) from aqueous nitrate media

Solven extraction separation of americium(III) from dilute aqueous nitrate media into n-dodecane by bis(2-ethylhexyl)sulfoxide (BESO) has been investigated over a wide range of experimentgal conditioins. Very poor extractablity of Am(III), necessitated the use of calcium nitrate as the salting-out agent. Effects of certain variables such as acidity, extractant concentration, salting-out agent concentration, organic diluents on the metal extraction by BESO have been examined in detail. By increasing the concentration of BESO in organic phase or calcium nitrate in aqueous phase, nearly quantitative extraction of americium even from moderate acidity is accomplished. Slope analyses applied to Am(III) distribution experiments from acidic nitrate solutions indicate predominant formation of the risolvated organic phase complex, Am(NO₃)₃)·3BESO for which equilibrium constant is found to be, log K_x=1.99. Extraction behavior of Am(III) has also been evlauated in the presence of several water-miscible polar organic solvents to stuy their possible synergistic effects on its extraction. Extractability of americium increased 5 to 10-fold withi increasing conentration of some of these additives, with maximum enhancement being observed in the presence of acetone or acetonitrile. Recovery of BESO from loaded americium is easily obtained using dilute nitric acid as the strippant.     

Extraction of Americium with Substituted Calix[4]Arenes from Alkaline Solutions

Extraction of ²⁴¹Am and ¹⁵²Eu from carbonate-alkaline medias with solutions of functionalized calix[4]arenes and their nonmacrocyclic analogs in m-nitrobenzotrifluoride was studied. The dependencies of the Am distribution ratios on pH of the aqueous phase in the range 10 -13.5 and on the position and nature of functional groups in the calixarene core were examined. The composition of extractable solvates of americium with functionalized calix[4]arenes was determined. Thiacalixarenes extract americium more efficiently from alkaline solutions, as compared to calixarenes, demonstrating higher Am/Eu separation factor. Functionalization of the calixarenes improves the Am extraction efficiency and Am/Eu separation factor as well. In the case of thiacalixarenes, functionalization considerably decreases the extraction efficiency and selectivity.     

Synergic extraction for recovery of americium from waste solution containing an excess of uranium

A method based on synergic extraction has been evolved for the recovery of tens of milligrams of americium from analytical wastes in 7-8M HNO₃ medium containing excess uranium as a two step procedure viz., (1) separation of uranium by contacting with TBP in dodecane and (2) recovery of americium by an extraction-cum-strip cycle using a synergic mixture of PMBP-TBP in dodecane after decreasing the acidity of the solution. Other transition metals such as iron found in significant proportion were separated from Am by using the difference in the kinetics of extraction of iron and americium into HPMBP-TBP-dodecane mixture by short duration contacts. About 99% of Am could be recovered into about 20% of its initial volume. This revised version was published online in July 2006 with corrections to the Cover Date.     

Separation of AM(III) by extraction from nitrate solutions using some quaternary benzylammonium salts

Benzyldimethyldodecylammonium nitrate and benzyltrioctylammonium nitrate were used for the extraction of Am(III) from aqueous nitrate solutions. The dependence of the extraction performance for Am(III) on the concentration of nitric acid, the kind and concentration of salting-out agents in the aqueous phase, and the kind of solvent was investigated. Americium is extracted by the above quarternary salts as a R₄NAm(NO₃)₄ associate. The extraction of Am(III) is compared with the extraction of lanthanides. The high differences in the distribution coefficients for lanthanides and americium can be utilized for the separation of lanthanides and americium.     

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.     

Purification of americium from assorted analytical waste in hydrochloric acid medium

During the simultaneous extraction of plutonium and uranium using anion exchange chromatographic technique from analytical waste in hydrochloric acid medium, ²⁴¹Am which is invariably present in the plutonium bearing fuel samples remains in the effluent. A two step separation scheme was developed for the recovery and purification of Am from the assorted waste to facilitate the disposal of large volume of aqueous waste and the purified Am solution was utilized for spectroscopic investigation. The separation scheme involved solvent extraction using 0.1 M TODGA + 0.5 M DHOA for separation of americium from Fe, Pb, Ni and Na followed by extraction chromatographic technique using CMPO on inert support as stationary phase for separation of Ca from Am. A systematic study on the extraction behavior of Am from hydrochloric acid medium revealed that out of four extraction systems well known for actinide partitioning namely 0.1 M TODGA + 0.5 M DHOA, 1 M DMDBTDMA, 0.2 M CMPO + 1.2 M TBP and 30% TRPO, only 0.1 M TODGA + 0.5 M DHOA extracts americium from 7.5 M HCl feed acidity. A comparative study involving CMPO solvent extraction and column chromatographic technique revealed that elution of Am from column is satisfactory as compared to inefficient stripping of Am from organic phase in solvent extraction technique using 0.1 M HNO₃. The purity of the final solution was checked for 17 elements of interest and was found to be 98% pure, while the overall recovery of this two step separation scheme was found to be 95%.     

Application of hollow fiber supported liquid membrane for the separation of americium from the analytical waste

Americium from analytical solid waste containing U and metallic impurities was separated using hollow fiber supported liquid membrane (HFSLM) technique impregnated with DHOA–TODGA from nitric acid medium. An aliquot of 5 g of the solid waste containing Am (19.95 mg) as minor actinide and of U (2,588 mg), Fe (1,360 mg), Ca (1,810 mg) and Na (3,130 mg) as major impurities was processed. The feed solution obtained after the dissolution of the residue in ~4 M HNO₃ was passed through HFSLM module. In the first stage using 1 M DHOA–dodecane U was recovered while Am and other impurities were left in the raffinate. In the second stage, 0.5 M DHOA + 0.1 M TODGA/dodecane was used for the separation of Am from other impurities. Though, majority of the elements were separated in this cycle, Ca was co extracted along with the americium. CMPO extraction chromatographic technique was used for further separation of americium from Ca. Significant decontamination factors were achieved in this three step separation process with respect to U, Fe, Na and Ca with ~77 % recovery of americium.     

Modeling and Flowsheet Design of an Am Separation Process Using TODGA and H4TPAEN

Recycling americium from spent fuels is an important consideration for the future nuclear fuel cycle, as americium is the main contributor to the long-term radiotoxicity and heat power of the final waste, after separation of uranium and plutonium using the PUREX process. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln(III)) and actinide (An(III)) cations into an organic phase containing the diglycolamide extractant TODGA, and then stripping Am(III) with selectivity towards Cm(III) and lanthanides. The water soluble ligand H₄TPAEN was tested to selectively strip Am from a loaded organic phase.Based on experimental data obtained by Jülich, NNL and CEA laboratories since 2013, a phenomenological model has been developed to simulate the behavior of americium, curium and lanthanides during their extraction by TODGA and their complexation by H₄TPAEN (complex stoichiometry, extraction and complexation constants, kinetics). The model was gradually implemented in the PAREX code and helped to narrow down the best operating conditions. Thus, the following modifications of initial operating conditions were proposed:

• •An increase in the concentration of TPAEN as much as the solubility limit allows.
• •An improvement of the lanthanide scrubbing from the americium flow by adding nitrates to the aqueous phase.

A qualification of the model was begun by comparing on the one hand constants determined with the model to those measured experimentally, and on the other hand, simulation results and experimental data on new independent batch experiments.A first sensitivity analysis identified which parameter has the most dominant effect on the process. A flowsheet was proposed for a spiked test in centrifugal contactors performed with a simulated PUREX raffinate with trace amounts of Am and Cm. If the feasibility of the process is confirmed, the results of this test will be used to consolidate the model and to design a flowsheet for a test on a genuine PUREX raffinate. This work is the result of collaborations in the framework of the SACSESS European Project.     

Development and Validation of the EXAm Separation Process for Single Am Recycling

The EXAm process aims at recovering americium alone. The principle of the EXAm process is based on the extraction of americium together with some light lanthanides having close values of distribution coefficients in high nitric acidity, while curium and other lanthanides remain in the aqueous phase. The TEDGA amide molecule is added in the aqueous phase to increase Am/Cm and Am/heavy Ln selectivity, because of the preferential complexation of curium and heavy lanthanides by this diglycolamide. The Am is subsequently selectively stripped from the light lanthanides.The full approach aiming at validating this complex process is illustrated in this paper.     

New approaches for the separation and determination of americium in soil samples using short column chromatography and alpha spectroscopy

This paper describes new approaches to digestion, accurate separation and determination of americium in soil samples by alpha spectrometry. The soil samples were obtained from surface and at a depth of 40?cm in a residential area. They were digested on a hot plate or in closed vessels heated in a microwave oven. The effect of decomposition methods on accuracy and reproducibility has been investigated. An extraction chromatography column is used to separate the americium from other actinide elements and interfering substances in the soil matrix. Prior to the determination of very low amounts of americium (100?ng?g^?1), electrodeposition at a current of 800?mA and a plating time of 150?min in the pH range of 2?C3 has been applied. The typical recovery of Am from the samples is 88?% when dissolution occurs in a microwave oven. This is higher than the typical recovery of 83?% that is observed when the samples are heated on a hot plate.     

Extraction of Am(III) in the presence of lanthanides and yttrium by benzyldimethyldodecylammonium nitrate from acidic nitrate solutions

We have investigated the effect of coextraction of lanthanides and yttrium on the distribution coefficients D_Am in the extraction of americium by benzyldimethyldodecylammonium nitrate (BDMLNNO₃) from nitrate solutions. In the coextraction of lanthanides, the extraction of Am(NO₃)₃ is suppressed, which is markedly manifested in the extraction of light lanthanides (La, Ce, Pr); of the series of lanthanides their extraction is the highest. The effect of nitric acid and the possibility of separation of lanthanides and americium by the application of three-stage multiple extraction is discussed.     

Efficient separation between trivalent americium and lanthanides enabled by a phenanthroline-based polymeric organic framework

Separation of the minor actinides (Am and Cm) from lanthanides in high-level liquid wastes (HLLW) is one of the most challenging chemical separation tasks known owing to their chemical similarities and is highly significant in nuclear fuel reprocessing plants because it could practically lead to sustainable nuclear energy by closing the nuclear fuel cycle. The solid phase extraction is proposed to be a possible strategy but all reported sorbent materials severely suffer from limited stability and/or efficiency caused by the harsh conditions of high acidity coupled with intense irradiation. Herein, a phenanthroline-based polymeric organic framework (PhenTAPB-POF) was designed and tested for the separation of trivalent americium from lanthanides for the first time. Due to its fully conjugated structure, PhenTAPB-POF exhibits previously unachieved stability under the combined extreme conditions of strong acids and high irradiation field. The americium partitioning experiment indicates that PhenTAPB-POF possesses an ultrahigh adsorption selectivity towards Am(III) over lanthanides (e.g., SF_{Am(III)/Eu(III)} = 3326) in highly acidic simulated HLLW and relatively fast adsorption kinetics in both static and dynamic experiments. Am(III) can be almost quantitatively eluted from the PhenTAPB-POF packed-column using a concentrated nitric acid elution. The high stability and superior separation performance endow PhenTAPB-POF with the promising alternative for separating minor actinides over lanthanides from highly acidic HLLW streams.     

Sensitivity of Americium and Curium Splitting Flowsheet and Running Procedure

As part of the 2006 French Act on sustainable radioactive waste and waste management, CEA has been developing a process, (EXAm), in order to separate americium from curium and fission product downstream of COEXTM or PUREX processes. The goal is to recover Am up to 99%. The first step mainly consists of splitting americium from curium thanks to the diamide in organic phase combined with a complexing agent in high nitric acid. The low separation factor between Am and Cm leads to a very sensitive process flowsheet towards operating conditions. It is then difficult to manage high recovery yields with good purity. A model has been built taking into account complexation equilibria by TEDGA in aqueous phase and extraction equilibria in organic phase for each element. This model was put into the PAREX code to find the correct flowsheet, and then to conduct sensitivity studies regarding several parameters such as feed flow, acidity, temperature, solvent flow and reagent concentration. These studies have pointed out a high correlation between americium yield and decontamination factor and, also, an equivalence between any change of the most sensitive parameters and a change in TEDGA concentration. A running procedure was followed during two hot tests: the main concept was to start with a less efficient process and then to improve it during the test in order to reach required performances by adjusting the TEDGA flow rate.     

Steric aspects of selectivity of organophosphorus extractants

This paper is devoted to the steric aspects of the efficiency and selectivity of extractants in the process of extraction of metal cations from acidic aqueous solution into a nonpolar phase. The extraction of uranium, plutonium, americium, and europium by tertiary carbamoylmethyl phosphine oxides and polydiphenylphosphinylmethyl benzenes have been studied. The separation factors of uranium and plutonium from americium are measured. Tertiary carbamoylmethyl phosphine oxides and diphenylphosphinylmethyl benzenes of the ortho type are characterized by unusually high separation factors. The diphenylphosphinylmethyl derivatives of benzene of the meta type do not possess a high selectivity in the process of separation of uranium and plutonium from americium, but are more efficient in extraction of americium.     

Use of complexones for the extraction separation of rare earth and transplutonium elements with amines

The extraction distribution and separation of rare earth elements and americium from the concentrated lithium nitrate solution with solutions of tertiary amines in organic solvents has been studied as a function of the composition and structure of complexones of the polyaminepolyacetic acid series by a radioactive tracer method. It has been found that diethylenetriaminepentaacetic acid is suitable for the separation of REE from americium(III). The apparent stability constants for the lanthanide complexes with EDTA and DTPA in concentrated litium nitrate solutions have been obtained by extraction, pH-metric titration and solubility. Using these constants, the optimum conditions of separation have been found and the separation factors of REE calculated. The calculated and experimental values are in good agreement. The optimum conditions for the separation of americium(III) from REE in a wide range of lanthanide and complexone concentrations (10⁻¹–10⁻⁶ M) have been determined.     

Extraction of americium and europium from perchloric acid solutions with N,N′-dialkyl-and N,N,N′,N′-tetraalkylpyridine-2,6-dicarboxamides

Extraction of americium and europium from perchloric acid solutions with pyridine-2,6-dicarboxamides was studied. The solvate numbers and Am/Eu separation factors were determined.     

Chromatographische Am-/Cm-Trennung in Schwach Sauren Oxidierenden Medien in der Wässrigen-und dem Chelatbildenden Austauscher Dowex-Al in der Stationären Phase

The separation of Am/Cm was studied in batch and dynamic experiments. It was achieved chromatographicaly on the chelating ion exchanger Dowex-Chelating-Resin-Al making use of the great difference between the complexing ability of trivalent and pentavalent oxidation states. For this purpose, the influence of some variables on the Am/Cm separation factor and on the stability of the adjusted pentavalent state was studied, e.g. the weight of ion exchanger, the time of contact and the pH-values of the solutions. Comparative investigations were carried out on the pentavalent ions of neptunium, plutonium and americium as well as on the hexavalent ions of plutonium and americium, where a significant difference in their behaviours was found.     

Chromatographic separation of americium from europium using bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine

The separation of americium(III) from europium(III) was achieved utilizing a bis-2,6-(5,6,7,8-tetrahydro-5,9,9-trimethyl-5,8-methano-1,2,4-benzotriazin-3-yl) pyridine (CA-BTP) chromatographic resin. The extraction chromatographic materials were prepared using various concentrations of CA-BTP. This new, hydrolytically stable extractant was impregnated on an inert polymeric support at 40% loading. The uptake of Am(III) and Eu(III) by this material from 0.1 to 4.0 M aqueous HNO₃ solutions was measured. The resulting dry weight distribution ratios, D _w , indicated a strong preference for Am(III) with little affinity for Eu(III). These results are similar to recently reported solvent extraction studies indicating a maximum uptake of Am(III) in the 0.5–1.0 M HNO₃ range. The resin preparation, performance, and characterization of the Am/Eu separation are reported herein.

     

Spectrochemical analysis of curium and americium samples

Spectrochemical procedures have been developed to determine impurities in americium and curium samples. The simultaneous separation of many impurity elements from the base material (americium and curium) is carried out with extraction and extraction-chromatographic methods using di(2-ethyl hexyl phosphoric acid (D2EHPA).

It is shown that part of the elements (alkalis, alkaline earths, silicon, tungsten, tantalum and other elements) are separated with extraction or sorption of americium and curium; the other part (rare earths, titanium, zirconium, niobium, molybdenum) with the Talspeak process.

Two fractions in the extraction chromatography and three fractions in the extraction separation of americium and curium, containing impurities, are analyzed separately by a.c. or d.c. arc spectrography. To increase the sensitivity of the spectrographic analysis and accelerate the burn-up of impurities from the crater of the carbon electrode bismuth fluoride and sodium chloride were used as chemically active substances. The extraction of impurities from weighed quantities of americium and curium samples of 5–10 mg permits the lower limit of determined impurity concentrations to be extended to 1 × 10⁻⁴–5 × 10⁻³% m/m.     

Extraction chromatographic behaviour of Am/IV/ in the system: H2SO4-K10P2W17O61-Primene JMT

The extraction chromatographic separation of Am/IV/ and Cm/III/ in the H₂SO₄-K₁₀P₂W₁₇O₆₁-Primene JMT system was studied. The elaborated method permitted to purify effectively americium. The yield of americium at an initial concentration of 10^–3M is about 93–95%, the curium content does not exceed 0.1% of the initial concentration.