Extraction of Americium(III) and Europium(III) with Two Open-Chain Crown Ethers of Amide Type

The extraction of Am³⁺ and Eu³⁺ from aqueous picric acid solution by N, N-dinaphthyl-N, N-diphenyl-3,6-dioxaoctanediamide (L^I) and 1, 1-(3, 6, 9-trioxaundecanedionyl)diphenothiazine (L^II) was investigated by a radioactive tracer technique. Extraction distribution ratios of Am³⁺ and Eu³⁺ have been measured as a function of pH, picric acid concentration, extractant concentration, diluent and temperature. The extraction of Am³⁺ is preferred to that of Eu³⁺ for both L^I and L^II, and the latter gives larger separation factor than the former. The equilibrium constants and thermodynamic parameters of extraction reactions were also calculated.     

Extraction of Am(III) and Eu(III) with dialkyldi (or mono) thiophosphinic (or phosphoric) acids

Extraction of Am(III) and Ln(III) from NaClO₄ medium with di(2-ethylhexyl)dithiophosphoric acid (DEHDTP), di(2-ethylhexyl)monothiophosphoric acid (DEHMTP), di(2-ethylhexyl)monothiophosphinic acid (DEHMTPI), dihexyldithiophosphinic acid (DHXDTPI), diheptyldithiophosphinic acid (DHPDTPI), dioctyldithiophosphinic acids (DODTPI), dinonyldithiophosphinic acid (DNDTPI), di(1-methylheptyl)dithiophosphinic acid (DMHDTPI) and di(2-ethylhexyl)dithiophosphinic acid (DEHDTPI) in xylene has been investigated. The order of the extraction selectivity for Am(III) is DEHDTPI > DEHDTP > DEHMTPI > DEHMTP, DHPDTPI > DODTPI > DHXDTPI > DNDTPI, DMHDTPI > DEHDTPI > DODTPI, for extractants with 2-ethylhexyl alkyl, straight chain alkyl, branch chain alkyl, respectively. Using 0.1 mol/l NaClO₄ solution as aqueous phase, the slope values of the logD-pH and logD-logC curves are not integers, and the slope values for Am(III) are slightly higher than those for Eu(III), for all extractants. The relationship between the slope value and extraction conditions can be described as: logS = alg(C _HA/C _M ^S/4)+b. In the presence of macro Eu(ClO₄)₃, the formula, logSF _Am/Ln = B-2log(C _HL-D _Ln/(D _Ln + 1)C _Eu), can well describe the relationship between separation factor and the extraction condition. A high separation factor (SF _Am/Eu = 2500) is obtained by solvent extraction with 0.5 mol/1 DEHDTPI in toluene from 1 mol/l NaNO₃ solution.     

Extraction chromatographic study on the separation of Am<Superscript>3+</Superscript> and Eu<Superscript>3+</Superscript> using ethyl-BTP as the extractant

Ethyl-substituted bis-triazinylpyridine (Et-BTP), a nitrogen containing soft-donor extractant, was used in investigations pertaining to the separation of Am³⁺ and Eu³⁺ from dilute nitric acid feed solutions by extraction chromatography using XAD-4 as the inert support, chlorinated dicarbollide as the modifier and 2-nitrophenyloctylether (NPOE) as the diluent. After carrying out a series of experiments, the optimum composition of the extractant mixture for the resin was found out to be 0.1 M Et-BTP and 0.025 M CCD in NPOE. Separation factor values were encouraging to carry out subsequent batch uptake studies at varying nitrate ion concentration which indicated favourable separation behaviour up to NaNO₃ concentration of 2 M. Column studies have been carried out and conditions for elution and separation of Am³⁺ from Eu³⁺ have been found out. Long term stability of the resin was also investigated.     

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.     

Convenient synthesis of (o-CF3Ph)2PS2H and evaluation in selective extraction of actinides over lanthanides

A convenient method was established for the synthesis of bis(ortho-trifluoromethylphenyl) dithiophosphinic acid (o-CF₃Ph)₂PS₂H. The three-step route consisted of reactions of PCl₃ with Grignard’s reagent, sulphur and NaHS in turn in liquid phase. The title compound was purified through the formation of ammonium salt (o-CF₃Ph)₂PS₂NH₄ and characterized with NMR and HRMS. Both chemical and radiation stability of title compound were examined. The investigation on selective extraction of Am³⁺ over Eu³⁺ was carried out from weak acidic aqueous phase with traces amount of radioactive elements ²⁴¹Am and ^152,154Eu. (o-CF₃Ph)₂PS₂H in toluene afforded excellent Am³⁺ extraction ability, with distribution ratio up to around 150, meanwhile the excellent actinides selectivity was obtained. Such performance indicated the potential application of (o-CF₃Ph)₂PS₂H in selective actinides extraction over lanthanides.     

Theoretical studies on the complexation of Eu(III) and Am(III) with HDEHP: structure,bonding nature and stability

Separation of trivalent lanthanides (Ln(III)) and actinides (An(III)) is a key issue in the advanced spent nuclear fuel reprocessing. In the well-known trivalent actinide lanthanide separation by phosphorus reagent extraction from aqueous komplexes (TALSPEAK) process, the organophosphorus ligand HDEHP (di-(2-ethylhexyl) phosphoric acid) has been used as an efficient reagent for the partitioning of Ln(III) from An(III) with the combination of a holdback reagent in aqueous lactate buffer solution. In this work, the structural and electronic properties of Eu³⁺ and Am³⁺ complexes with HDEHP in nitric acid solution have been systematically explored by using scalar-relativistic density functional theory (DFT). It was found that HDEHP can coordinate with M(III) (M=Eu, Am) cations in the form of hydrogen-bonded dimers HL₂^- (L=DEHP), and the metal ions prefer to coordinate with the phosphoryl oxygen atom of the ligand. For all the extraction complexes, the metal-ligand bonds are mainly ionic in nature. Although Eu(III) complexes have higher interaction energies, the HL₂^- dimer shows comparable affinity for Eu(III) and Am(III) according to thermodynamic analysis, which may be attributed to the higher stabilities of Eu(III) nonahydrate. It is expected that this work could provide insightful information on the complexation of An(III) and Ln(III) with HDEHP at the molecular level.     

Separation of Am(III), Cm(III) and Eu(III) by electro-spun polystyrene-immobilized CyMe4-BTPhen

The synthesis of a novel 5-(4-vinylphenyl)-CyMe₄-BTPhen actinide selective ligand using selenium free synthetic procedures is reported. For the first time, we report the electrospinning of this actinide selective ligand into a polystyrene fiber and investigate its selective removal of Am(III) from Eu(III) and Am(III) from Cm(III). At 4?M HNO₃, the resulting fibrous solid extractant produced separation factors of SF_Am/Eu?≈?57 and a small, but significant separation of SF_Am/Cm?≈?2.9.     

An unusual extraction behavior of americium (III) and dioxouranium (VI) from picric acid medium using 18-crown-6 as neutral oxodonor

The extraction behavior of Am³⁺ and UO₂ ²⁺ is investigated employing chloroform solution of 18-crown-6 as the organic phase and picrate solution at pH 3.0 as the aqueous phase. In contrast to the commonly observed behavior, the extraction of Am³⁺ is preferred to that of UO₂ ²⁺. This unusual separation behavior is investigated as a function of several variable parameters such as crown ether concentration, picric acid concentration, inert electrolyte concentration, nature of diluent etc. Thermodynamic parameters are also evaluated.     

Solvent extraction studies of plutonium(IV) and americium(III) in room temperature ionic liquid (RTIL) by di-2-ethyl hexyl phosphoric acid (HDEHP) as extractant

Solvent extraction of Pu(IV) and Am(III) from aqueous nitric acid into room temperature ionic liquid (RTIL) by an acidic extractant HDEHP (di-2-ethyl hexyl phosphoric acid) was carried out. The D values indicated substantial extraction for Pu(IV) and poor extraction for Am(III) at 1M aqueous nitric acid concentration. However at lower aqueous nitric acid concentrations (pH 3), the Am(III) extraction was found to be quantitative. The least squares analysis of the extraction data for both the actinides ascertained the stoichiometry of the extracted species in the RTIL phase for Pu(IV) and Am(III) as [PuH(DEHP)₂]³⁺, AmH(DEHP)²⁺. From the D values at two temperatures, the thermodynamic parameters of the extraction reaction for Pu(IV) was calculated.     

Extraction behaviors of Eu,Th, U and Am with diamides+thenoyltrifluoroacetone

N,N-dimethyl-N,N-dihexyl-3-oxapentanediamide, DMDHOPDA, N,N-dihexyl-3-thiopentanediamide, DHTPDA and N,N-dihexyl-3-oxapentanediamide, DHOPDA were synthesized and tested for the synergistic extraction of Eu³⁺, Th⁴⁺, UO ₂ ²⁺ , NpO ₂ ⁺ and Am³⁺ with thenoyltrifluoroacetone (HTTA). Although Eu³⁺, Th⁴⁺, UO ₂ ²⁺ and Am³⁺ were not extracted by DHTPDA or DHOPDA alone, they were extracted synergistically when combined with HTTA. Analysis of the dependency of extraction on pH and extractant concentration indicated that the dominant extracted species were Eu(TTA)₃(A), Th(TTA)₃(A)(X), UO₂(TTA)₂(A) and Am(TTA)₃(A) (where A is diamide, and X is chloroacetate or ClO ₄ ^– ).     

Density functional theory insight into Eu(III) and Am(III) complexes with two 2,6-dicarboxypyridine diamide-type ligands

Extraction complexes of Eu(III) and Am(III) with two 2,6-dicarboxypyridine diamide-type ligands L–A and L–B (Fig. 1) are studied by density functional theory (DFT). At both B3LYP/6-31G(d)/RECP and MP2/6-31G(d)/RECP levels of theory, the geometrical optimizations of the structures of the complexes can achieve the same accuracy and obtain the same geometrical configuration. At the B3LYP/6-311G(d,p)/RECP level of theory Eu³⁺ and Am³⁺ prefer to form [ML]³⁺ complexes under the solvation conditions, and the Am(III) complexes with L–A are more stable than the corresponding Eu(III) complexes. In the system with the ligand L–B, both [ML]³⁺ and [ML(NO₃)₃] species are very unstable.     

Separation of trivalent americium and europium by purified Cyanex 301 immobilized in macro porous polymer

The present work confirms the high separation ability of purified Cyanex 301 towards trivalent americium over europium in liquid-liquid extraction. Solvent 2-nitrophenyl octyl ether (NPOE) lowered the partitioning of Am³⁺ but remained the separation ability over europium. Solvent toluene and 3-octanone lowered the separation factor to 1000. It is feasible to separate Am³⁺ from Eu³⁺ by Cyanex 301 which was immobilized in the macro porous polymer (MPP). 3-Octanone is a suitable solvent for dissolving NH₄OH-saponified Cyanex 301 and MPP is a suitable solid supported material for column operation. A five-step column experiment demonstrated the feasibility to separate Am³⁺ from Eu³⁺ in column which was packed with Cyanex 301-impregnated MPP.     

Extraction separation of Am(III) and Eu(III) using divalent quadridentate Schiff bases-bis-salicylaldehyde ethylenediamine

For the selective extraction of Am(III) and Eu(III), quadridentate divalent phenolic Schiff bases-bis-salicylaldehyde ethylenediamine (H₂salen) was investigated as a kind of extractant. The influences of alkaline cation, inorganic anion, ionic strength, pH and the concentration of H₂salen on the distribution ratio of Am(III) and Eu(III) were investigated in detail. As a result, Am(III) and Eu(III) made anionic 1:1 complexes with the ligand (H₂salen) and could be extracted into nitrobenzene as ion-pairs with a suitable monovalent counter anion in the aqueous solution, the extracted species were possibly of the type Am(H₂salen) Eu(salen)Cl and Eu(H₂salen)Cl₃, respectively. The extractability of Eu(III) was significantly stronger than that of Am(III) and the maximum separation factor, SF_(Am/Eu), was 96 at pH 4.0. The results indicated that H₂salen had good selectivity for Am(III) and Eu(III).     

Studies on the separation treatment of high-level liquid waste by bisamide podand(I): Extraction and separation of An(III) from Ln(III)

A process for actinide(III) and lanthanum(III) extraction separation from high-level liquid waste (HLLW) was proposed, with N,N,N',N'-tetraoctyl diglycolamide (TODGA) as the extractant, tri-n?butyl phosphate (TBP) as the phase modifier and 2,6-bis[1-(propan-1-ol)-1,2,3-triazol-4-yl]pyridine (PyTri-Diol or PTD) as hydrophilic stripping agent. This ‘hot test’ was successfully carried out, achieving 99.92% removal of americium-241 (²⁴¹Am) with a separation factor SF_(Eu/Am) of 3.8 × 10³ in the actinide(III) product solution. The results show that bisamide podand extractants can effectively realize the extraction and separation of actinide(III) and lanthanum(III) from Chinese commercial HLLW and thus have a bright practical application potential for the treatment of commercial HLLW.     

Radiation stability of benzyldibutylamine and benzyldimethyldodecylammonium nitrate in the extraction of lanthanides and americium

The radiation stability was investigated of organic phases containing tertiary benzyldialkylamines and quaternary benzyltrialkylammonium salts which are sultable for the separation of lanthanides and americium from irradiated nuclear fuel. Attention was paid to changes of the extraction properties in Eu(III) and Am(III) extraction. The influence of the individual components forming the organic phase (extractant, solvent, solubilizer and nitric acid) on the decrease of the extraction capacity of the organic phase after irradiation is discussed. The greatest changes in the distribution coefficients D_Eu and D_Am after irradiation were shown for extraction in the presence of nitric acid. As regards the absorbed dose, these systems can be considered as stable in comparison with organophosphorus extractans.     

The effect of ammine,ethanoate, trichloro- and trifluoroethanoate ligands on tris(2,4-pentanedionato) chromium(III) formation in high pH aqueous solution

The yields of tris(2,4-pentanedionato)chrvmium(III) (Cr(acac)₃) formed in the presence of either the ammonia (Am), ethanoate (ET), trichloroethanoate (TCE), or trifluoroethanoate (TFE) ligand in high pH aqueous solution, were compared with those from a medium containing only hydroxyl and water as the principal ligands besides the acac. The presence of Am, ET, and TCE drastically reduced the yields at pH’s 9.5–10.5, 7.5–9.0/9.5–11.0, and 9.0–12.0, respectively in increasing order ET > Am < TCE. The role of Am is attributed mainly to the oxo-bridged species ((OH)_m(H₂O)_nAm_5-(m+n)Cr(O)(OH)CrAm_5-(m+n)(H₂O)_n(OH)_m)^3-2m (1), ((OH)_m(H₂O)_nAm_5-(m+n)Cr(O)₂CrAm_5-(m+n)(H₂O)_n(OH)_m)^2-2m (2), and ((OH)_m(H₂O)_nAm_5-(m+n)Cr(O)(OH)CrAm_4(m+n)(H₂O)_n(OH)_m+1)^2-2m (3). 2 is the most deactivating species mainly on the basis that the Cr-O bond of the oxo-bridge is suggested as being stronger than the Cr-O bond of the hydroxo-bridge. As for ET and TCE, oxo-bridged polymeric ethanoato- and trichloroethanoatochromium(III) species are also proposed as the main origin of the drastic deactivation of the reaction not observed for TFE due possibly, to the insignificance of oxo-bridges in tnfluoroethanoatochromium(III) species.     

Extraction of europium and americium by a mixture of CMPO and dicarbollide

The extraction of Eu³⁺ and Am³⁺ by a mixture of CMPO and dicarbollide in nitrobenzene has been studied. The synergetic effect of dicarbollide is pronounced at low acidities but still lower than for previously studied DBDECMP. Separation properties towards Am/Eu pair are small.     

Studies on the extraction of americium(III) from aqueous nitrate media by sulfoxides

Solvent extraction behaviour of Am(III) from dilute nitric acid media with sulfoxides (R₂SO) in Solvesso-100 has been investigated over a wide range of conditions. Very poor extractability of Am necessitated the use of salting-out agents, viz., nitrates of Al, Mg, Ca, Li and NH ₄ ⁺ . Effects of certain variables such as acidity, extractant concentration, saltingout agent, temperature etc., on metal extraction by sulfoxides have been examined systematically. For a fixed sulfoxide concentration, extraction attains a maximum value up to around 0.2–0.4M HNO₃ and decreasing above 1M HNO₃. In contrast, increasing the concentration of sulfoxide (0.8M DISO, 1.3M DBuSO) gives almost quantitative Am extraction up to 1M HNO₃. For satisfactory extraction, di-n-octyl as well as di-n-hexyl sulfoxide are the most suitable extracting agents. Extractability of Am increases with increasing amounts of all the salting-out agents studied and their effect follows the sequence: Al³⁺>Mg²⁺>Ca²⁺>Li⁺>NH ₄ ⁺ ; this is also the relative dehydrating effect of the cations. The species extracted would appear to be Am(NO₃)₃.3R₂SO. Americium is easily stripped with 1–3M HNO₃ solutions from the loaded organic phase. Extraction decreases with increasing temperature, indicating the extraction to be exothermic. Extraction from partially non-aqueous solutions was also investigated.     

Extraction of tri- and tetravalent actinides with dihexyl N,N-diethylcarbamoylmethyl phosphonate (DHDECMP) and TBP from nitric acid solutions

Extraction of trivalent (Pu³⁺, Am³⁺, actinides and Eu³⁺, a representative of lanthanides) and tetravalent (Np⁴⁺ and Pu⁴⁺) actinides has been studied with dihexyl N,N-di-ethylcarbamoylmethyl phosphonate (DHDECMP) in combination with TBP in benzene from 2M nitric acid. The stoichiometries of the species extracted were found to be M(NO₃)₃·(3–n) TBP·n DHDECMP (for trivalent ions) and M(NO₃)₄·(2–n) TBP·n DHDECMP (for tetravalent ions) by the slope ratio method. The extraction constants evaluated (from the distribution data) indicate that for tetravalent ions (with solvation number two) the extraction constant increases when TBP (Kh=0.17) molecules are successively replaced by more basic DHDECMP (Kh=0.34) molecules. However, for trivalent ions (with solvation number three) when TBP molecules are totally replaced by DHDECMP molecules stereochemical factors appear and instead of increase, a substantial decrease in extraction constants is observed for Eu³⁺ and Am³⁺, a lesser decrease being observed for Pu³⁺ (larger ion).     

Complexation Studies of Bidentate Heterocyclic N-Donor Ligands with Nd(III) and Am(III)

A new bidentate nitrogen donor complexing agent that combines pyridine and triazole functional groups, 2-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)pyridine (PTMP), has been synthesized. The strength of its complexes with trivalent americium (Am³⁺) and neodymium (Nd³⁺) in anhydrous methanol has been evaluated using spectrophotometric techniques. The purpose of this investigation is to assess this ligand (as representative of a class of similarly structured species) as a possible model compound for the challenging separation of trivalent actinides from lanthanides. This separation, important in the development of advanced nuclear fuel cycles, is best achieved through the agency of multidentate chelating agents containing some number of nitrogen or sulfur donor groups. To evaluate the relative strength of the bidentate complexes, the derived constants are compared to those of the same metal ions with 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2-pyridin-2-yl-1H-benzimidazole (PBIm). At issue is the relative affinity of the triazole moiety for trivalent f element ions. For all ligands, the derived stability constants are higher for Am³⁺ than Nd³⁺. In the case of Am³⁺ complexes with phen and PBIm, the presence of 1:2 (AmL₂) species is indicated. Possible separations are suggested based on the relative stability and stoichiometry of the Am³⁺ and Nd³⁺ complexes. It can be noted that the 1,2,3-triazolyl group imparts a potentially useful selectivity for trivalent actinides (An(III)) over trivalent lanthanides (Ln(III)), though the attainment of higher complex stoichiometries in actinide compared with lanthanide complexes may be an important driver for developing successful separations.