Selectivity of bis[n-butyl(hydroxyl)phosphoryl]dibenzo crown ether endoreceptors in metal extraction from nitric acid solutions

Diphosphorylated dibenzo crown ethers with 4,4′(5′)-bis[n-butyl(hydroxy)]phosphoryl substituents at the benzene rings of dibenzo-18-crown-6 (I), dibenzo-21-crown-7 (II), and dibenzo-24-crown-8 (III) were prepared and studied with the aim of developing new highly effective and selective extractants for recovery and separation of metals. Extraction of a solution containing Al, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Ge, In, K, La, Li, Mg, Mn, Mo, Na, Ni, Pb, Re, Sc, Sr, Tl, V, Y, and Zn (10 ppm each) and an Am(III) solution in 0.01–5 M HNO₃ with 0.05 M solutions of the endoreceptors in chloroform was studied. For endoreceptor III, the maximal distribution ratios of metals D _m ^max are ranked in the following order: Sc (>10³) > Am (162) > Mo (129) > V (75.9) > In (29.3) > Bi (16.5) > Fe (4.7) > Rb (1.0) > Pb (0.34) > Ga (0.18) > Ge (0.11) > Al, B, Ba, Ca, Cd, Co, Cr, Cu, K, La, Li, Mg, Mn, Na, Ni, Re, Sr, Tl, V, Zn (<0.1). The distribution ratio D _m in all the examined equilibrium systems decreases with increasing HNO₃ concentration in the range 0.01–3 M. The fact that this decrease is significantly less pronounced than that for the known organophosphorus acids suggests complex extraction mechanism, presumably via formation of scorpion-like host-guest complexes. Thus, diphosphorylated dibenzo crown ethers with phosphoric acid substituents are very strong and highly selective endoreceptors in extraction of Sc, Mo, In, and Am from nitric acid solutions and can be used in practice for preconcentration of these elements and their separation from concomitant impurities.     

Influence of the structure of organophosphorus substituents on the extraction ability of diphosphorylated crown ethers

Extraction properties of lariat crown ethers were studied. Dibenzo-substituted crown ethers of a new class, with electron-donor side phosphoryl groups -P(O)R₂ (R = iso-C₃H₇O, n-C₄H₉O, C₆H₅), were proposed as extracting agents. The oxygen atoms of the phosphoryl groups form additional bonds with metal ions in the extractable complexes. Extraction of 31 metals from 0.01–7 M HNO₃ with five diphosphorylated derivatives of 18-crown-6 and 21-crown-7 was studied. Diphosphorylated endoreceptors were prepared by introduction of organophosphorus fragments into the structure of dibenzo crown ethers. The extraction properties of these compounds depend on the electron-donor properties of the phosphoryl oxygen. If the sum of the reaction constants of the substituents at the phosphorus atom of these groups is ?1.77 or more negative, the phosphoryl oxygen is coordinated with the metal of the extracted metal salts and the endoreceptos are effective and selective extracting agents for the following metals (the maximal distribution ratio is given): Tl (1.1) ≈ Rb (1.1) < Bi (5.7) < Re (26) < Mo (36) < Sc (>103). In this case, the extraction ability of diphosphorylated dibenzo crown ether increases by a factor of 10²–10³ as compared to that of the unsubstituted analogs. The resulting compounds can be used as endoreceptors of new generation with unique extraction properties.     

Extraction of Am and Rare-Earth Elements from Nitric Acid Solutions with Ethyl Bis(diphenylphosphinylmethyl)phosphinate

Extraction of HNO₃ and microamounts of Am, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y from HNO₃ solutions with solutions of ethyl bis(diphenylphosphinylmethyl)phosphinate in dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the effective extraction constants of HNO₃ and Am were calculated. With increasing number of phosphoryl groups in the extractant molecule, the extraction of Am(III) and rare-earth elements from HNO₃ solutions increases.     

Influence of the ring size in diphosphorylated dibenzo crown ethers on extraction of metals from nitric acid solutions

Extraction of metals from 0.1–7 M HNO₃ with 0.05 M chloroform solutions of functionalized crown ethers containing (n-C₄H₉O)₂P(O)- fragments and differing in the polyether ring size (18-crown-6, 21-crown-7, 24-crown-8) was studied. An increase in the size of the macroring in diphosphorylated dibenzo crown ethers leads to an appreciable increase in the performance of the extractants toward a number of metals, due to participation of phosphoryl groups in the complexation. At the same time, the reactivity of the macroring varies insignificantly, which decreases the selectivity of the recovery of metals forming host-guest complexes. These features should be taken into account when designing new macrocyclic extractants of the lariat type.     

Extraction of Am,Eu, Tc,and Pd from nitric acid solutions with phosphorylated calixarenes

Extraction of Am, Eu, Pd, and Tc from 0.1–3.0 M HNO₃ with solutions of phosphorylated calix[n]arenes in m-nitrobenzotrifluoride (NBTF) was studied. The ring size and position of phosphoryl groups (in the upper or lower rim) affect the extraction of Am and Eu significantly and that of Tc and Pd only slightly. Calix[4]arenes phosphorylated at the upper rim extract Am and Eu considerably better than do their analogs with substituents in the lower rim and substituted calix[6]arenes. Compounds with the phosphoryl group linked to the calixarene core by the methylene bridge show the highest extracting performance. In contrast to monodentate phosphine oxides, in calix[4]arenes the size of the alkyl substituent at the P atom strongly affects the efficiency of extraction of the radionuclides. With a decrease in the length of the alkyl radical in substituents ?CH₂P(O)Alk₂, the distribution ratios of all the radionuclies, as a rule, decrease. With a decrease of Alk in ?CH₂P(O)PhAlk, the distribution ratios increase for Eu and Am but remain unchanged for Tc and Pd. Calix-arenebis(methylenediphosphonates) with the propoxy substituents at the P atom extract Eu and Am hundreds times more efficiently than do their analogs with methoxy, isopropoxy, and butoxy substituents. The possibility of joint recovery of Am, Eu, Tc, and Pd from nitric acid solutions with calix[4]arenes containing dialkylmethylenephosphine oxide substituents in the upper rim was demonstrated. The prevalent species formed in the extraction of Tc are complexes of the composition M₂L. The composition of complexes formed by calix-arenes with Am and Eu depends on the preparation procedure.     

Extraction Properties of Butyl Bis(dibutoxyphosphinylmethyl)phosphinate in Nitric Acid Solutions

The extraction of HNO₃ and microamounts of U(VI), Th(IV), Sc(III), REE(III), and Am(III) nitrates from HNO₃ solutions with solutions of butyl bis(dibutoxyphosphinylmethyl)phosphinate in organic diluents was studied. The stoichiometry of the extractable complexes was determined, and the apparent extraction constants were calculated. The capability of the extractant to recover the examined elements from nitric acid solutions grows with an increase in the number of phosphoryl groups in its molecule. The recovery of the metal ions into the organic phase becomes more efficient in going to more polar organic diluents.     

Separation of Am and Cm by Extraction from Weakly Acidic Nitrate Solutions with Tributyl Phosphate in Isoparaffin Diluent

Trivalent transplutonium (TPE) and rare earth (REE) elements are extracted to more than 80% with 30% TBP in Isopar M from solutions containing 0.06–0.5 M HNO₃ and a salting-out agent, NH₄NO₃, in a concentration of ≥6 M. The elements are stripped from the organic phase with 0.1 M HNO₃. The Am(III)/Eu separation factors vary from 1.8 to 2, which can be used for their extraction separation. The Cm/Am(III) separation factors in 0.06–3 M HNO₃ are in the range from 1.1 to 1.2; therefore, to separate these elements, higher oxidation states of Am, Am(VI) and Am(V), should be used. The effect of various factors on the stability of Am(VI) was examined, and the conditions of the existence of Am(VI) and Am(V) in ≤0.1 M HNO3 solutions containing ~8 M NH₄NO₃ were determined. Curium is extracted with 30% TBP in Isopar M virtually completely, whereas americium only partially (≤30%) passes into the organic phase in the form of Am(III). In the process, high degree of separation of Cm from Am(V) remaining in the aqueous phase is reached (≥99.9%).     

Effect of the Structure of <Emphasis Type="Italic">o</Emphasis>-Methyleneoxyphenyldiphosphine Dioxides on Their Extractive Power and Selectivity in Nitric Acid Solutions

Extraction of trace amounts of Pu(IV), U(VI), Th(IV), Am(III), and REEs(III) from nitric acid solutions with o-methyleneoxyphenyldiphosphine dioxides with phenyl (I) and butyl (II) substituents at the phosphoryl group is studied. The stoichiometry of extractable complexes in dichloroethane is determined. Changing the butyl substituents for phenyl ones increases the effective extraction constants of Pu(IV), Th(IV), and Am(III) and decreases that of U(VI). In extraction from 3 M HNO³, the Pu(IV)/U(VI) and Th(IV)/U(VI) partition coefficients are higher with reagent I, and the Pu(IV)/Am(III) and U(VI)/Am(III) partition coefficients, with reagent II.     

Extraction of rare-earth elements and americium from acid solutions with alkyl derivatives of dibenzo- and dicyclohexano-18-crown-6

Extraction of rare-earth elements (REEs) and Am(III) from acid solutions with alkyl-substituted crown ethers dibenzo-and dicyclohexano-18-crown-7 in the chloroform-water system was studied. Dicyclo-hexano-18-crown-6 and its alkyl derivatives extract REEs and Am(III) in the presence of trichloroacetic acid (HTCA) considerably better, compared to dibenzo-18-crown-6 and its alkyl derivatives and to the systems containing HNO₃ and HC1O₄ instead of HTCA. The distribution ratios of the cerium-group REEs are considerably higher than those of the yttrium-group REEs. In all the cases, the metal to crown ether ratio in theextractable complexes is 1:1.     

Extraction of long-lived radionuclides from nitric acid solutions using an extractant based on dibutyl hydrogen phosphate and chlorinated cobalt dicarbollide

Chlorinated cobalt dicarbollide (CCD), when added to concentrations of 0.25 M to a solution of dibutyl hydrogen phosphate (HDBP) in m-nitrobenzotrifluoride (MNBTF), increases the distribution ratios of trace amounts of Eu and Am without changing the slope (tan α ～ 2) of their dependences on HDBP concentration in the 0–1.5 M range. At [CCD]/([CCD] + DBPA]) = 0.2–0.22, the synergistic effect is observed in the entire range of HDBP concentrations in extraction of these elements from 1.0 and 2.5 M HNO₃. In this case, HDBP suppresses the extraction of Cs with CCD in the area below the synergistic maximum, where antagonism is observed in the extraction of Cs. Polyethylene glycol (PEG, Slovafol-909) was added to the extraction mixture to improve the extraction of Sr. The extremum is attained at its concentration in the solvent with HDBP of ～0.033–0.065 M, which is smaller than that in the absence of HDBP by a factor of 1.5–2.5. With increasing concentration of HDBP in the HDBP-CCD-PEG-MNBTF extraction system, the slopes for Eu and Am are 1.3 and 0.6, whereas the slopes for Cs and Sr decrease nonlinearly and amount to ?1.8 and ?1.3, respectively. With increasing concentration of HNO₃, D for Eu, Am, and Cm decreases in proportion to the HNO₃ concentration to the power of ?3 irrespective of the PEG concentration, and for Cs and Sr, to the power of ?2 in the presence of PEG, whereas in the PEG-free systems the dependences are nonlinear. The synergistic extractant is characterized by higher (by an order of magnitude) solubility of metal solvates as compared to the HDBP-MNBTF system (concentration of Eu in the extractant >0.163 M). The extractant containing HDBP (1.1 M), CCD (0.23 M), and Slovafol-90 (0.065 M) in MNBTF is suggested for combined recovery of rareearth (REE) and transplutonium elements (TPE) and of Cs and Sr from high-level waste (HLW) after reprocessing of spent nuclear fuel (SNF) with high burn-up.     

Extraction properties of tetrasubstituted methylenediphosphine dioxides in nitric acid media

Extraction of HNO₃ and microamounts of REE(III), U(VI), Th(IV), Zr(IV), Sc(III), Ca(II), Sr(II), and Ba(II) nitrates from solutions of HNO₃, LiNO₃, and NH₄NO₃ with solutions of tetrasubstituted methyl-enediphosphine dioxides R₂P(O)CH₂P(O)R′₂ [R = R′ = p-Tol (I); R = R′ = Ph (II); R = Ph, R′ = Bu (III); R = R′ = Bu (IV)] in 1,2-dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the apparent extraction constants of HNO₃ and REE were calculated. The efficiency of the REE(III) extraction from 0.5–3 M HNO₃ increases in the series of extractants IV < III < II < I and decreases with an increase in the REE atomic number. The ratio of the apparent extraction constants of REE(III) nitrates with reagents II and IV in the form of disolvates, characterizing an increase in the extraction ability of tetrasubstituted methylenediphosphine dioxides on replacement of butyl groups at the P atoms by phenyl groups (anomalous aryl strengthening), decreases along the REE series.     

Extraction Properties of Trioxides of Pentasubstituted Diethylenetriphosphines in Nitric Acid Solutions

Extraction of HNO₃ and microamounts of U(VI), Th(IV), Sc(III), and REEs(III) from HNO₃ solutions with solutions of trioxides of symmetrical dioctyltriphenyldiethylenetriphosphine and pentaphenyl-diethylenetriphosphine in dichloroethane was studied. The stoichiometry of the extractable complexes was determined, and the effective extraction constants of HNO₃ and REEs were calculated. As the number of phosphoryl groups in the extractant molecule increases, the extraction of metal ions from nitric acid solutions is enhanced. Replacement of the octyl radicals at the terminal phosphorus atoms by the phenyl radicals is accom-panied by an increase in extraction of metal ions from solutions with the HNO₃ concentration exceeding 3 M.__________Translated from Radiokhimiya, Vol. 47, No. 1, 2005, pp. 72–76.Original Russian Text Copyright © 2005 by Turanov, Karandashev, Bondarenko.     

Effect of ionic liquids on the extraction of Am from HNO3 solutions with diphenyl(dibutylcarbamoylmethyl)phosphine oxide in dichloroethane

Addition of small (1?C5 vol %) amounts of ionic liquids (ILs) increases the Am(III) distribution ratio in the system with diphenyl(dibutylcarbamoylmethyl)phosphine oxide (Ph₂Bu₂) by more than 2 orders of magnitude. With 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₄mim]⁺Tf₂N^?) used as IL, the Am(III) extraction is possible even from 8 M HNO₃, which is important in radiochemical analysis of process and environmental samples, because many procedures are based on the transfer of solid samples into 8 M HNO₃. The extraction data show that the extractable Am(III) complex contains three Ph₂Bu₂ ligands, an IL anion, and two NO ₃ ^? anions.     

Extraction of rare-earth and transplutonium elements with dibutyl hydrogen phosphate in <Emphasis Type="Italic">m</Emphasis>-nitrobenzotrifluoride

The extraction of rare-earth (REE) and transplutonium (TPE) elements, with Ce, Eu, and Am as examples, from aqueous HNO₃ with dibutyl hydrogen phosphate (HDBP) in m-nitrobenzotrifluoride (MNBTF) was studied. The diluent effect on the Eu and Am extraction with dibutyl hydrogen phosphate was examined at various HNO₃ concentrations in the aqueous phase. Based on the data obtained, a mechanism of REE extraction was suggested and the parameters of extraction equations for the initial lanthanide concentrations in the aqueous phase from 0.1 to 100 g l^?1 (counting on metal), HDBP concentration in MNBTF of 0.1–2 M, and HNO₃ concentration in the range 0.5–8 M were calculated. Isotherms of HNO₃ extraction with HDBP solutions of various concentrations were obtained. The possibility of attaining higher concentrations of REE solvates in their extraction with HDBP in MNBTF was demonstrated.     

Extraction of metal ions from aqueous solutions of mineral acids with crown ether-ionic liquid systems

The extraction of U(VI), Sr, and Cs from solutions of mineral acids (HNO₃, HCl) with a crown ether, cis-syn-cis-dicyclohexyl-18-crown-6 (DCH18C6-A), dissolved in ionic liquids (ILs), 1-butyl-3-methyl-imidazolium derivatives (bmimPF₆, bmimBF₄, bmimTf₂N), was studied. The best physicochemical characteristics (solubility in the aqueous phase, viscosity, hydrophobicity, etc.) are exhibited by a solution of DCH18C6-A in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (bmimTf₂N). The metal distribution ratios (D _M) in the extraction with a 0.01 M DCH18C6-A solution are 80 for CsNO₃, 78 for CsCl, and 162 for Sr(NO₃)₂. With an increase in the HNO₃ and HCl concentrations, D _M decreases, and with 1 M acids it does not exceed 1. The U(VI) extraction from nitric acid solutions with a 1 M solution of DCH18C6-A in bmimTf₂N initially increases with an increase in the aqueous phase acidity, with D _U(VI) reaching 5.4 in 4 M HNO₃, but then decreases in the interval 4–8 M HNO₃, whereas in the extraction with a 1 M solution of tributyl phosphate (TBP) in bmimTf₂N D _U(VI) monotonically increases with an increase in the HNO₃ concentration to 8 M. From hydrochloric acid solutions, U(VI) is extracted with solutions of DCH18C6-A in bmimTf₂N with the D _U(VI) values characteristic of solutions of DCH18C6-A in nonpolar organic diluents. On the whole, ILs as solvents exhibit unusual properties in the extraction of alkali and alkaline-earth elements from neutral solutions and of U(VI) with TBP from concentrated nitric acid solutions.     

Extraction properties of polyfunctional P,N-containing podands with diphenylphosphorylacetamide terminal groups in nitric acid solutions

The extraction of HNO₃ and microamounts of U(VI), Th(IV), Sc(III), and REE(III) nitrates from HNO₃ solutions with dichloroethane solutions of phosphorus-containing podands containing two terminal Ph₂P(O)CH₂C(O)NH groups linked by a di-or triethylene glycol chain was studied, and the stoichiometry of the extractable metal complexes was determined. The compounds extract the metal ions from nitric acid solutions more efficiently than does (dibutylcarbamoylmethyl)diphenylphosphine oxide. With increasing length of the polyethylene glycol chain, the extraction of HNO₃ increases, but the degree of recovery of REE(III) ions from HNO₃ solutions of the concentration exceeding 3 M decreases.     

Sorption recovery of U(VI), Pu(IV), and Am(III) from nitric acid solutions with solid-phase extractants based on Taunit carbon nanotubes and polystyrene supports

Sorption procedures were developed for recovering U(VI), Pu(IV), and Am(III) with solid-phase extractants (SPEs) prepared by impregnation of Taunit carbon nanotubes and polystyrene supports with diphenyl( dibutylcarbamoylmethyl)phosphine oxide (CMPO) and tri-n-octylphosphine oxide (TOPO) The impregnation and actinide recovery were performed in the batch mode and using microcolumns. Procedures for support impregnation and SPE preparation are described. Conditions were found for sorption recovery of U(VI), Pu(IV), and Am(III) from 3 M HNO₃ solutions. The possibility of actinide desorption was demonstrated. The effect of macrocomponents on the degree of actinide recovery was examined.     

Extraction of f Elements and Technetium from HNO3 Solutions with Solutions of Alkyl (N,N-Diethylcarbamoylmethyl)phenylphosphinates

Phosphinic acid derivatives, alkyl (N,N-diethylcarbamoylmethyl)phenylphosphinates (ADPs) were synthesized, studied, and tested as extractants for f elements and technetium at the Mayak Production Association. The distribution factors of these elements D were studied in relation to the ADP and HNO₃ concentrations. The influence exerted by the structure of the alkoxy group at the P atom on DAm and DEu in extraction of Am(III) and Eu(III) (chosen as examples) from nitric acid solutions with solutions of ADPs in dichloroethane was examined. The differences between the distribution factors of Am(III), Pu(IV), U(VI), and Tc(VII) are sufficiently high for complete separation of these elements with a high degree of purification in one step of extraction with ADP solutions. The changes observed in the IR spectrum of the 2-ethylhexyl ADP upon complexation with Pr(III) suggest high complexing power of this reagent toward lanthanide ions. The spectrometric data suggest bidentate coordination of the metal with the chelating groups of the reagent.     

Synergic extraction of Ce(III) from HNO<Subscript>3</Subscript> solutions with a mixture of CCD and HDBP ZS in a polar diluent

The extraction of Ce(III) from HNO₃ solutions with a mixture of chlorinated cobalt dicarbollide (CCD) and dibutyl hydrogen phosphate (HDBP) or its zirconium salt (HDBP ZS) in m-nitrobenzotrifluoride was studied by the method of isomolar series. A considerable synergic effect S was observed, reaching a maximum in a mixture of HDBP with CCD at the molar ratio HDBP : CCD = 7 : 1 (S = 100). The highest Ce(III) distribution ratios D _Ce are observed with mixtures of CCD and HDBP ZS (1 : 6 and 1 : 4). An increase in the HNO₃ concentration causes changes in D _Ce and S to different extents depending on the type of HDBP ZS. The synergic effect was attributed to the formation of coordination compounds that are more hydrophobic than the initial compounds and have stronger bonds of Ce(III) with the ligands.     

Use of ozone for dissolving high-level plutonium dioxide in nitric acid in the presence of Am(V,VI) ions

Plutonium dioxide recovered in the course of reprocessing of SNF from WWER reactors (so-called high-level PuO₂) was subjected to dissolution in 0.6–3.0 M HNO₃ in the presence of Am(III) ions under ozonation with an ozone-oxygen mixture containing 30–180 mg l⁻¹ O₃. Measurements of the rate of the PuO₂ dissolution in 3 M HNO₃ in the temperature interval from 30 to 80°C showed that, with an increase in the ozone concentration in the ozone-oxygen mixture from 30 to 180 mg l⁻¹, the dissolution rate increases by a factor of 4–5. The acceleration of the PuO₂ dissolution is attributed to the formation of Am(V,VI) by homogeneous oxidation of Am(III) ions with ozone dissolved in HNO₃. The Am dioxocations formed act as PuO₂ oxidants and are continuously regenerated by the oxidation of Am(III) with ozone. This assumption is confirmed by an additional increase in the dissolution rate, observed on introducing Am(III) into the initial electrolyte for the PuO₂ dissolution.