EXTRACTION OF TRIVALENT LANTHANIDES AND ACTINIDES BY A SYNERGISTIC MIXTURE OF THENOYLTRIFLUOROACETONE AND A LINEAR POLYETHER

Abstract

Mixtures of a linear polyether, l,13-bis[8-quinolyl]-l,4,7,10,13-pentaoxatridecane, K-5, and thenoyltrifluoroacetone, HTTA, have been shown to exhibit synergistic character in the extraction of trivalent lanthanides and actinides. The effect of the addition of K-5 to the organic phase on the extractions of Ce(III), Eu(III), Tm(III), Am(III), Cm(III), Bk(III), and Cf(III) by HTTA in chloroform from 0.5M NaNO₃ at 25°C has been measured. These results indicate the extraction is enhanced by the formation of M(TTA)₃K-5 adduct in the organic phase. The organic phase stability constants for the formation of these synergistic species have been calculated for all the metals studied. The magnitude of these organic phase stability constants for K-5 are similar to other common neutral donors. The order of stability does not follow the normal trend based on charge-to-radius ratio, but follows a pattern based on size, with Am(III) being the most stable.     

EXTRACTION OF SOME LANTHANIDES AND ACTINIDES BY 15-CROWN-5 THENOYLTRIFLUOROACETONE MIXTURE IN CHLOROFORM

The extraction of Eu³⁺, Tm³⁺, and Yb³⁺ by a mixture of thenoyltrifluoroacetone (HTTA) and 15-Crown-5 (15C5) in chloroform from a 0.1-ionic strength acetate buffer was investigated. Large enhancement in the extraction for these lanthanides was obtained when a mixture of the two extractants was used. Experimental data indicated that this enhancement is a result of the formation of a lanthanide adduct in the organic phase of the type Ln(TTA) ³° 2CE, where CE refers to a crown ether. The synergistic factors (S.F.), mixed extraction constants and formation constants of the different adducts in the organic phase were found to take the sequence Eu³⁺ > Tm³⁺ > Yb³⁺.

Using 12-Crown-4 (12C4), no enhancement in the extraction was observed. This was explained in terms of the small cavity size of 12C4 relative to 15C5.

The same system comprising HTTA-15C5 was also studied for the extraction of Pu⁴⁺, Am³⁺, Nd³⁺, and Er³⁺. Moderate enhancement was obtained for the extraction of Am³⁺ while no increase in the extraction was found for Pu⁴⁺.The metal concentration in the aqueous phase was found to largely affect the S.F. values for Nd³⁺ and Er³⁺.     

SYNERGISTIC EXTRACTION OF LANTHANIDES(III) BY TRIOCTYLMETHYLAMMONIUM NITRATE AND TRIBUTYL PHOSPHATE

ABSTRACT

The synergistic action of tributyl phosphate in the extraction of La(III), Pr(III)Nd(III), Sm(III), Eu(III), Gd(III), Dy(III), Ho(III), Er(III)and Y(III) with trioc-tylmethylammonium nitrate was studied. The synergistic effect is diluent dependent. It is pronounced with a mixed dodecane/xylene diluent, and is weak with mixed heptane/xylene and hexane/xylene diluents as well as with pure xylene diluent. Two or three synergistic complexes are formed simultaneously in the organic phase. Their composition is (A₊)(Ln(N0₃)) ₄),.2B~), (A₊))(Ln(N0₃))J.3B"), and (A₊)) ₂) (Ln(N0₃)) ₅).BJ-) (Ln is a lanthanide(IM), A+ is a trioc-tylmethylammonium cation and B is a tributyl phosphate molecule). The stability of the synergistic complexes generally decreases with increasing atomic number of the lanthanides(III). The synergism enhaces the efficiency of the lanthanide(III) extraction with trioctylmethylammonium nitrate, but deteriorates its selectivity. The separation factors for the Pr(III)-Nd(III) and Eu(III)-Gd(III) pairs are gradually suppressed at increasing concentration of tributyl phosphate.     

EXTRACTION OF U(VI), Pu(IV) AND Th(IV) BY SOME TRIALKYL PHOSPHATES

ABSTRACT

This paper reports the data on the extraction of U(VI), Pu(IV) and Th(IV) from nitric acid by tri-isobutyl phosphate, tri-n-amyl phosphate, tri-isoamyl phosphate and tri-n-hexyl phosphate and provides a comparison of their extract ion behaviour with that of tri-n-butyl phosphate. Data on the third phase formation in the system Th(NO₃) ₄ ^?HNO₃ ^?1.1 M trialkyl phosphate/n-dodecane are also presented.     

SYNERGISTIC SELECTIVE EXTRACTION OF ACTINIDES(III) OVER LANTHANIDES FROM NITRIC ACID USING NEW AROMATIC DIORGANYLDITHIOPHOSPHINIC ACIDS AND NEUTRAL ORGANOPHOSPHORUS COMPOUNDS

ABSTRACT

New aromatic dithiophosphinic acids (R₂PSSH) with R = C₆H_5?, ClC₆H_4?, FC₆H_4? and CH₃C₆H_4? were synthesized, characterized and tested as potential separating agents for trivalent actinides over lanthanides. The extraction of Am(III), Eu(III) and other lanthanides was carried out from nitric acid medium with mixtures of R₂PSSHS and neutral organophosphorus compounds. There was no detectable extraction when R₂PSSHS were used alone as extractants for either Am(III) or Eu(III) (D_AM,EU.< 10^?3) under the experimental conditions used in this study. High separation factors (D_AM/D_EU > 20) with D_AM > 1 were achieved in the nitric acid range 0.1-1 mol/L by means of a synergistic mixture of bis(chloro-phenyl)dithiophosphinic acid + tributylphosphate (TBP), irioctylphosphine oxide (TOPO) or tributylphosphine oxide (TBPO). The high radiation resistance (up to 10⁶ Gy absorbed γ-doses) of the extractants was also demonstrated.     

EXTRACTION OF URANIUM(IV,VI), PLUTONIUM(III) AND NITRIC ACID BY 30% TRIBUTYL PHOSPHATE (TBP) IN DODECANE

Abstract

Data on the distribution of uranium(IV,VI), plutonium(III) and nitric acid between 30 vol.% TBP in dodecane and aqueous nitrate solutions also containing hydrazine nitrate were mathematically described by empirical equations. This made it possible to present distribution ratios of the extracted components as functions of concentrations and temperature at a single variable being varied and other variables being kept constant. Salting-out and self-salting-out action of the electrolytes present in the system as well as mutual replacement of the extracted components from the organic phase are shown.     

THE EXTRACTION BY N.N'TETRABUTYLGLUTARAMIDES II. EXTRACTION OF U(VI), Pu(IV) AND SOME FISSION PRODUCTS

The extraction of U(VI) and Pu(IV) from aqueous nitrate solutions by N,N'-tetrabutylglutaramide (TBGA) has been investigated. At low acidities, the extraction takes place via the formation of respectively UO₂(NO₃)₂. TBGA and Pu(NO₃)₄. TBGA which seem to be linked with additionnal molecules of TBGA in the second coordination sphere of the metal. When the saturation of TBGA by UO₂ ²⁺solutions is reached, the uranyl complex reorganizes to give a polymer (UO₂(NO₃)₂ TBGA)_x.

At high acidities, the anionic complexes : [UO₂(NO₃)₃, ^?] [HTBGA⁺] and probably [HPu(NO₃)₆?] [HTBGA+] are observed.     

SEPARATION OF ACTINIDES AND LANTHANIDES FROM ACIDIC NUCLEAR WASTES BY SUPPORTED LIQUID MEMBRANES

ABSTRACT

Supported liquid membranes, SLM, consisting of a solution of 0.25 M octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and 0.75 μ tributylphosphate (TBP) in decalin absorbed on thin micropocous polypropylene supports, have been studied for their ability to perform selective separations and concentrations of actinide and lanthanide ions from synthetic acidic nuclear wastes. The permeability coefficients of selected actinides (Am, Pu, U, Np) and of some of the other major components of the wastes have been measured using SLMs in flat-sheet and hollow- fiber configurations. The results have shown that with the thin (25 μm) flat-sheet SLMs, using Celgard® 2500 as support, the membrane permeation process is mainly controlled by the rate of diffusion through the aqueous boundary layers. With the thicker (430 μmpar; hollow-fiber SLMs, using Accurel® hollow-fibers as support, the membrane permeation process Is controlled by the rate of diffusion through both the SLM and the aqueous boundary layers. Hollow-fibers SLMs exhibited lower permeability coefficients and longer life-times. The experiments have shown that the actinides can be very efficiently removed from the synthetic waste solutions to the point that the resulting solution could be considered a non-tramsiranic waste (less than 100 mCi/g of disposed form). The work has demonstrated that actinide removal from synthetic Waste solutions is a feasible chemical process at the laboratory scale level. The process is characterized by the typical featirces of SLM's processes, i.e. (a) very small quantities of extractants (b) hlilh feed/strip volume ratios, resulting in a corresponding concentration factor of the actinides, (c) simplicity of operation, which should result in lower capital and operating cost, and (d) negligible solvent enttainment.     

SYNERGIC EXTRACTION OF COBALT(II) BY STRUCTURALLY RELATED CROWN ETHERS AND THENOYLTRIFLUOROACETONE

ABSTRACT

Cobalt (II) was extracted from perchlorate aqueous media by thenoyltrifluoroacetone (HTTA)alone and mixed with 12-Crown-4 (12C4) 15-Crown-5 (15C5) 18-Crown-6 (18C6)dibenzo-18-Crown-6 (Dbl8C6)dicyclohexyl-18-Crown-6 (Dchl8C6) or dicyclohexyl-24-Crown-8 (Dch24C8), in chloroform. The extraction constant of the chelate (K20) the extraction constant of the mixed species (K21), the synergic factor (S.F.) and the formation constant of the extracted adducts (β₂₁) were evaluated. The adduct stoichiometry was found to have the general formula Co(TTA)₂CE, irrespective of the crown ether (CE) used. It was found that no specific cavity size is required for the adduct formation. The synergic values K₂₁, S.F., and β₂₁as related to the crown ether took the order Dch24C8 > 18C6 > Dchl8C6 > 15C5 > Dbl8C6 > 12C4, which could be explained in terms of the crown ether basicity rather than the correspondence between the cavity size of the crown ether and the cobalt(II) crystal radii. The sequence 18C6 > Dchl8C6 > Dbl8C6 was interpreted in terms of the withdrawing ability of Dch and Db as substitutes in reducing the basic character of the adjacent crown ether oxygen donors.     

SOLVENT EXTRACTION OF SCANDIUM(III), YTTRIUM(III), LANTHANIDES(III), ANDDIVALENT METAL IONS WITH SEC -NONYLPHENOXY ACETIC ACID

ABSTRACT

Such physicochemical properties of sec-nonylphenoxy acetic acid (CA-100) as the solubility in water, acid dissociation constant in water, dimerization constant in heptane, and distribution constant in organic solvent-water were measured by two-phase titration. The extraction behaviors of scandium (III), yttrium (III), lanthanides (III), and divalent metal ions from hydrochloric acid solutions with CA-100 in heptane have been investigated, and the possibilities of separating scandium (yttrium) from lanthanides and divalent metal ions have been carefully discussed. The stoichiometries of the extracted metal complexes were investigated by the slope-analysis technique. The effect of the nature of diluent on the extraction of yttrium (III) with CA-100 has been studied and correlated with the dielectric constant.     

SOLVENT EXTRACTION OF URANIUM( VI) AND THORIUM( IV) FROM NITRATE MEDIA BY CARBOXYLIC ACID AMIDES

ABSTRACT

A series of nineteen N-alkyl carboxylic acid amides (R.CO.NHR') has been prepared, in which the alkyl groups R and R' have been varied in order to introduce different degrees of steric complexity into the compounds. A smaller number of N,N-dialkyl amides (R.CO.NR₂) and non-substituted amides (R.CO.NH₂) has also been prepared for comparison purposes. These amides were characterized by measurement of their boiling points, melting points, refractive indices and densities.|The solvent extraction of uranium(VI) and thorium(IV) from sodium nitrate media by solutions of the amides in toluene was studied. Increasing steric bulk of the alkyl groups R and R' was found to cause a marked decrease in the extraction of thorium, with a much smaller effect on the extraction of uranium, thus considerably enhancing the separation between these metals. Vapour pressure osmometry studies indicate that the N,N-alkyl amides are self-associated in toluene solution, with aggregation numbers up to about 2.5 for 0.6 M solutions at 35°C. In contrast, the N,N-dialkylamides behave as monomers under these conditions. The distribution ratios for the extraction of uranium and thorium show second- and third-order dependences, respectively, on the extractant concentration for both the N-alkyl and N,N-dialkyl amides.     

EXTRACTION OF ACTINIDES BY BIFUNCTIONAL PHOSPHINIC ACID RESIN

ABSTRACT

The extraction of U(VI), Am( III), Pu( IV), Np( IV) and ThIV) by bifunctional phosphinic acid resin of various cross linkages is reported as function of nitric acid concentration. From the comparison of the distribution coefficient values it is suggested that the recovery of these actinide elements from waste solutions as we II as their mutual separations is possible by using phosphinic acid resin.     

DILUENT AND EXTRACTANT EFFECTS ON THE ENTHALPY OF EXTRACTION OF URANIUM(VI) AND AMERICIUM(III) NITRATES BY TRIALKYL PHOSPHATES

ABSTRACT

The effect of various diluents such as n-hexane, n-heptane n-octane, isooctane, n-decane, n-undecane, n-dodecane, n-tetradecane, n-hexadecane, cyclohexane, benzene, toluene, p-xylene, mesitylene and o-dichlorobenzene on the enthalpy of extraction of uranyl nitrate by tri-n-amyl phosphate (TAP) over the temperature range 283 K - 333 K has been studied. The results indicate that the enthalpy of extraction does not vary significantly with the diluents studied. Also enthalpies of extraction of uranyl nitrate and americium(III) nitrate by neutral organo phosphorous extractants such as tri-n-butyl phosphate (TBP), tri-n-amyl phosphate (TAP), tri-sec-butyl phosphate (TsBP), tri-isoamyl phosphate )TiAP) and tri-n-hexyl phosphate (THP) have been studied. An attempt has been made to explain the trends, on the basis of the nature of the solvate formed and the different terms which contribute to the overall enthalpy change.     

EXTRACTION OF Se,Y, AND LANTHANIDES BY QUATERNARY AMMONIUM SALTS

The separation of Sc and Y from the lanthanides by extraction with various quaternary ammonium salts was investigated. Aliquat-336,methyltrioctylammonium nitrate (MTOA), methyldibutylhexadecylammonium nitrate (MDBHDA) and tributylhexadecylammonium nitrate (TBHDA) were used as extractants. The synthesis of MDBHDA and TBHDA from industrial products is described. From the results obtained in the extraction studies of REE as a function of the parameters of aqueous and organic phases, we have determined the optimal separation conditions. The salting-out action in these systems of a great number of cations such as Al³⁺, Fe³⁺, Mg³⁺, Cu³⁺, Ni³⁺, Li³⁺, Cs³⁺, was investigated. To determine the functional dependences of the separation factors for the REE, the viscosity of the water layer around the ion was used.     

EXTRACTION OF MOLYBDENUM(VI) BY PRIMENE JMT

ABSTRACT

Distribution of molybdenum (VI) between aqueous sulfuric acid solution and an organic solution containing Primene JMT has been studied.

The aqueous solutions consist of ammonium molybdate with acid concentration in a pH range 2 - 6.5, the concentration of amine in the organic phase being 0.1 mol/dm³ in benzene. The presence of various species in the aqueous phase is considered and the equilibrium composition of substances in the organic phase is determined. The extraction mechanism is discussed.     

A COUNTER CURRENT EXPERIMENT FOR THE SEPARATION OF TRIVALENT ACTINIDES AND LANTHANIDES BY THE SETFICS PROCESS

ABSTRACT

The SETFICS process, a variation of TRUEX process, was developed for the recovery of Am and Cm from acidic waste solution and the separation of actinides (III) and light lanthanides. The process uses the general TRUEX solvent as the extracting reagent and a DTPA-sodium nitrate solution for selective stripping of actinides(III). The basic flow sheet is composed of four steps: extraction-scrubbing; acid stripping; actinide(III) stripping; and lanthanide stripping.

To demonstrate the usefulness of the SETFICS process, a counter current experiment was conducted using a real TRUEX product solution. Americium and curium were successfully recovered with a solution of 0.05 M DTPA-4 M NaNO₃ (pH 2.0). Although the actinide(III) product solution contained Sm and Eu, the decontamination factor of ¹⁴⁴Ce/²⁴¹Am was 72, and most of the light lanthanides, specifically La, Ce, Pr, Nd, were removed. At least 80 % of the lanthanides were separated from the Am and Cm end products. In order to minimize the acidity in the actinide(III) stripping step, the nitric acid which extracted with the trivalent metals was previously removed with a solution of 0.5 M NaNO₃ (pH 2.0) in the “acid stripping” step.     

SOLVENT EXTRACTION OF TRIVALENT LANTHANIDES AND YTTRIUM FROM NITRATE MEDIA BY DIALKYL SULPHOXIDES

The solvent extraction of the trivalent rare-earth metals (the lanthanides and yttrium, Ln³⁺) from nitrate media by xylene solutions of some dialkyl sulphoxides (R₂SO, where R=alkyl) was studied. The salting-out effect of added metal nitrate (5.00 M) increases in the order: NH₄NO₃>NaNO₃>LiNO₃. Extraction is independent of pH in the range from 2 up to at least 4, but decreases gradually below pH 2 due to the competing extraction of nitric acid.

Vapour-pressure osmometry data indicate that the dialkyl sulphoxides are not appreciably self-associated under the conditions studied (0.10 to 0.60M in xylene or toluene solutions at 30°C), which permits the use of organic-phase concentration terms (in place of activities) in the slope-analysis studies. The distribution ratios for the extraction of yttrium, gadolinium and lutetium show a third-order dependence on the concentration of the sulphoxide in the organic phase, with a slightly higher dependence (3.3) for lanthanum. In addition, the mole ratio of nitrate to metal in the loaded organic phase is close to 3, which suggests that the stoichiometry of the extracted complexes is Ln(NO₃)₃(R₂SO)₃.

Increasing the steric bulk of the substituent alkyl groups (R) in the sulphoxides causes a marked decrease in metal extraction, and a reasonable correlation exists between the extraction of a given metal and the sum of the steric parameters of the alkyl groups in each of the sulphoxides used. In traversing the lanthanide series, the extraction increases in the interval La to Sm, and decreases thereafter to the end of the series. The behaviour of yttrium most closely resembles that of thulium or ytterbium.     

SOLVENT EXTRACTION OF Pa(V) and Th(IV) BY TRIPHENYLPHOS-PHINE AND TRIPHENYLARSINE OXIDES FROM HYDROCHLORIC ACID MEDIUM

The extraction of Pa(V) by both ph₃PO and Ph₃AsO in chloroform from HCl medium is performed. The extraction stoichiometry for each system is proposed which is assumed to proceed through the formation of monosolvate. The extraction behaviour of Pa(V) by both extractants is quantitatively described by an empirical equation for each case. The obtained data show that the extraction power of Ph₃AsO is much higher than the corresponding value of PH₃PO. This difference is ascribed to the difference in their electronic structure. The effect of using different diluents is studied. In the same way, the extraction of Th (IV) by both extractants from HCl medium is described and the separation factors for both systems are calculated and compared.     

A STUDY OF COMPLEXES YIELDED BY HNO3 Fe(III)AND Eu(III) EXTRACTION FROM NITRATE MEDIA WITH ACIDIC Zr(IV) AND Hf( IV) DI-2-ETHILHEXYLPHOSPHATES

Possible reasons for significant enhancement of solvent extraction of some metals with dialkylphos-phoric acids in the presence of Zr(IV) and Hf(IV) are critically discussed, taking into consideration both the literature and the autors'data on the structure of acidic salts formed by these acids with Zr(IV) and Hf(IV). The chemistry of extraction of nitric acid, FeUII) and Eu ( I I I ) with Zr(IV) and Hf(IV) salts of di-2-ethy1hexy1 phosphoric acid (HX) has been studied using IR and ³¹P NMR spectroscopy. Nitric acid is extracted by these salts due to interaction with their acceptor sites that results in the formation of a new polymeric extractant with bidentate anions of two types, (X-H-X)- and (X-H-N0₃)_. Protons of these groups can be exchanged with metal cations extracted, e.g., with Fe(III) or Eu(I 11 ), heteropolynuc1 ear complexes with non-equivalent (chelating and bridge) N0₃ anions being formed during the extraction. The composition and structure of coordination polyhedrons formed around Zr(IV), Hf(IV), Fe(III) and Eu(III) have been determined. The reasons for a higher extraction ability of the salts studied for Fe(III) and Eu(III) versus D2EHPA itself are described.