Extraction of rare earth elements by high molecular weight amines from nitric acid solutions

Extraction of trivalent rare earth elements by a high molecular weight primary amine /decylamine/ from 0.5–3M nitric acid solutions, containing potassium phosphotungstate /K₁₀P₂W₁₇O₆₁/, has been investigated. The effect of nitric acid and potassium phosphotungstate concentration of the organic solvent, and lanthanides ionic radii upon distribution coefficients has been studied. It has been established that decylamine solutions in chloroform can be used for the group isolation of rare earth elements and for their separation.     

Extraction of rare earth elements by primary high molecular weight amines from hydrochloric acid solutions

Extraction of trivalent lanthanides: La, Ce, Nd, Eu, Tb, Tm, Yb by primary high molecular weight amines from 0.5–3M hydrochloric acid solutions, containing complex-forming agent potassium phosphotungstate /K₁₀P₂W₁₇O₆₁/ has been investigated. The effect of hydrochloric acid, potassium phosphotungstate and amine concentration, the length of primary amine alkyl chain, organic solvents nature and elements ionic radii on distribution coefficients have been studied. It has been established that the system can be used for group isolation and separation of rare earth elements.     

Sequential separation of actinides and lanthanides by extraction chromatography using a CMPO-TBP/XAD7 column

CMPO/TBP sorbed on Amberlite XAD7 resin was used for the separation of actinides and lanthanides from nitric acid solutions by extraction chromatography. The distribution ratios of actinides and lanthanide fission products (Ce, Eu) as a function of acid concentration and some complexing agents were determined. In strong HNO₃ medium (>1 mol/l) the tri-, tetra- and hexavalent actinides as well as the lanthanides have shown great affinity for the CMPO/TBP/XAD7 sorbent. The same behavior was found in HCl medium except for trivalent actinides and lanthanides which show lower distribution values in the same acid range. The effect of some complexing agents as DTPA and ammonium oxalate were also investigated. In DTPA only hexavalent actinides showed higher distribution value. On the basis of these differences, an alternative procedure for actinide-lanthanide separation and actinides from each other is proposed.     

The EURO-GANEX Process: Current Status of Flowsheet Development and Process Safety Studies

A new hydrometallurgical grouped actinide extraction process has been developed to separate the transuranic actinide ions from dissolved spent fuel solution (after an initial uranium extraction cycle). This “EURO-GANEX” process is aimed towards the homogeneous recycling of plutonium and minor actinides in a future closed fuel cycle. The separation process is based on the co-extraction of actinides and lanthanides from aqueous nitric acid into an organic phase followed by selective co-stripping of actinides. A suitable organic phase has been formulated and distribution ratios determined for lanthanides, actinides and some problematic fission products under extraction and stripping conditions. The process flowsheet has been proven on surrogate feed solutions as well as with spent fast reactor fuel; excellent recoveries of the actinides and good decontamination factors from the lanthanides and other fission products were obtained. A variation on the EURO-GANEX flowsheet (the “TRU-SANEX” process) has now been designed to produce separate Pu+Np and Am+Cm products for heterogeneous recycling. Progress on underpinning process chemistry and safety studies as well as flowsheet tests are summarized.     

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).     

Uptake of actinides and lanthanides from nitric acid by dihexyl-N,N-diethylcarbamoylmethylphosphonate adsorbed on chromosorb

Batchwise uptake of Am(III), Pm(III), Eu(III), U(VI) and Pu(IV) by dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) adsorbed on chromosorb (CAC) at nitric acid concentrations between 0.01 to 6.0M has been studied. The difference between the uptake behavior of Pu(IV) as compared to other actinides and lanthanides is discussed. The Am(III) and U(VI) species taken up on CAC were found to be Am(NO₃)₃·3CMP and UO₂(NO₃)₂·2CMP, respectively. The equilibrium constants for the formation of these species have been evaluated and compared with those of similar species formed in liquid-liquid extraction. Batchwise loading of Pm(III) on CAC from 3.0M HNO₃ has also been studied.     

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.     

Extraction of actinides in two-phase water-poly(ethylene glycol)—Salt systems in the presence of potassium phosphotungstate

Extraction of actinides has been examined in two-phase aqueous systems based on poly(ethylene glycol) (PEG) from sulfate solutions in the presence of potassium phosphotungstate, which forms strong complexes with ions of tri- and tetravalent transuranium elements. Extraction of these complexes by aqueous PEG solution is complete in contrast to that of penta- and hexavalent actinides. Conditions have been chosen for the separation of actinides in different oxidation states.     

On the mechanism of trivalent actinide extraction in the system HDEHP—Lactic acid with DTPA

The dependence of the distribution coefficients on the hydrogen ion concentration and HDEHP concentration in the process of extraction from lactic acid solutions in the presence of DTPA and without it has been investigated. It has been shown that when the lactate ion concentration is higher than 0.01M, Cm is extracted predominantly as the first lactate complex. The presence of DTPA does not change the extraction mechanism. Similarity of the observed regularities for trivalent actinides and lanthanides is confirmed by the extraction of Bk(III), Ce(III), and Eu(III). It is suggested that the nature of carbonic acid used in TALSPEAK-process greatly influences the efficiency of group separation of TPE and lanthanides. It is supported by some experimental data. The extraction and stability constants of the first lactate complex (Cm Lact²⁺) have been found to be: K_e=2, β ₁ ⁰ = 7,7 · 10³. In the practical lactic acid concentration range (1 M) the unextractable complex, Cm Lact₃, is also formed in the aqueous phase. The stability constant of this complex has been found to be β ₃ ⁰ = 1.2 · 10⁷.     

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.     

N-(n-Alkyl)-N′-diphenylphosphorylureas as a new type of extractants for preconcentration of actinides and lanthanides

N-(n-Alkyl)-N′-diphenylphosphorylureas Ph₂P(O)NHC(O)NHC _n H_2n+1 (n = 6–10) were synthesized by the reaction of diphenylphosphoryl isocyanate with primary n-alkylamines C _n H_2n+1NH₂. The products (especially N-diphenylphosphoryl-N′-n-octylurea) are efficient extractants capable of extracting actinides and lanthanides from nitric acid solutions with high distribution coefficients. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 374–379, February, 2008.     

Chirality and Polarity in the f‐Block Borates M4[B16O26(OH)4(H2O)3Cl4] (M=Sm,Eu, Gd,Pu, Am,Cm, and Cf)

The reactions of trivalent lanthanides and actinides with molten boric acid in high chloride concentrations result in the formation of M₄[B₁₆O₂₆(OH)₄(H₂O)₃Cl₄] (M=Sm, Eu, Gd, Pu, Am, Cm, Cf). This cubic structure type is remarkably complex and displays both chirality and polarity. The polymeric borate network forms helical features that are linked via two different types of nine‐coordinate f‐element environments. The f–f transitions are unusually intense and result in dark coloration of these compounds with actinides.     

Sorption Recovery of Transplutonium Elements from Nitric Acid Solutions with Arsenazo Group Reagents

Sorption recovery of actinides and lanthanides from nitric acid solution with arsenazo group reagents, activated carbon modified with these reagents, and chelating sorbents containing arsenazo functional groups was studied.     

Synergistic extraction of uranium(VI) by lower fatty acids in the presence of amines and its separation from some lanthanides

The synergistic extraction of UO₂(II) in a chloroform solution of propionic, butyric and valeric acids (HA) in the presence of some aliphatic and aromatic amines (B) has been investigated. The effect of various variables, like the concentration of hydrogen and metal ion, carboxylic acid and amine on extraction has been studied. The composition of the synergistic adducts has been determined on the basis of slope analysis and the species is proposed to be UO₂A₂B₂ 2HA. The extraction constants (K_ex) have been calculated and the relative effectiveness of the amines as synergists is compared. Extraction data have been used to separate UO₂(II) from lanthanides, like Ce(III), Nd(III), Gd(III), Eu(III) and Yb(III).     

Synergic extraction of some lanthanide and actinide elements by a mixture of bis/2-ethyl hexyl/phosphoric acid and dinonylnaphthalene-sulfonic acid in aromatic diluents

Extraction of lanthanides and actinides were found to be synergically enhanced by a mixture of bis/2-ethyl hexyl/phosphoric acid /HA/ and dinonylnaphthalene sulfonic acid /HD/ in aromatic diluents covering a wide range of dielectric constant. The main extracted species is found to be in the form MA₂H_m–1D_m. Experimental results indicate that the extraction mechanism is governed by the extraction of HD in the organic phase.     

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.     

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).     

Preparation of125I labeled testosterone derivatives for use in radioimmunoassays

A study for separation and sequential recovery of uranium and plutonium from nitric acid solutions by extraction chromatography using tributyl phosphate (TBP)/Amberlite XAD7 as stationary phase is presented. Distribution ratios of actinides, lanthanides and fission products were obtained. The column capacity was investigated and actinides retention conditions were established. Finally, U-Pu sequential separation was studied as well as the U and Pu recovery yields from nitric solutions containing Am/fission products were determined.     

Acetyl-containing phosphine oxides as extractants for actinides and lanthanides

Extraction capability and selectivity of acetyl-containing phosphine oxides R₂P(O)CMe₂CH₂C(O)Me (R = Pr, Bu, n-C₅H₁₁, n-C₆H₁₃, n-C₈H₁₇, Ph) toward actinides (U^VI, Th^IV) and trivalent lanthanides (La^III, Nd^III, Ho^III, Yb^III) were studied. The new ligands were shown to be more efficient and selective in the extraction of uranium, thorium, and heavy lanthanides from nitric acid solutions into chloroform as compared to the known extractants such as carbamoylphosphine oxide Ph₂P(O)CH₂C(O)NBu₂, trioctylphosphine oxide (n-C₈H₁₇)₃P(O), and tributyl phosphate (n-BuO)₃P(O).     

New conceptual process for the extraction of actinides based on oxapentane-diamides

Several diamide derivates were synthesized in our laboratory. The extraction of actinides and some fission products by these compounds were studied. N,N,N’,N’-tetra-(2-ethylhexyl)-3-oxa pentanediamide [TEHOPDA) was proven to be a suitable extractant for the removal of actinides from nitric acid solution. The actinides can be stripped from the loaded solvent by the dilute nitric acid. TEHOPDA showed a high loading capacity to actinides and lanthanides with a mixture of n-octanol and kerosene as the diluent. Considering the effective-extraction and easy-stripping of actinides, 0.25 mol/l TEHOPDA — 30% n-octanol + 70% kerosene was selected as the solvent. A cascade extraction experiment was carried out with the simulated dissolver solution of spend fuel as feed. 99.99% U and 99.999% Am, Pu, and Np were extracted in a 4-stage test. Based on the experimental results, a conceptual reprocessing process was proposed.