METAL EXTRACTION BY ALKYL SUBSTITUTED DIPHOSPHONIC ACIDS. PART 4 P,P′-DI(2-ETHYLHEXYL) BUTANEDIPHOSPHONIC ACID

ABSTRACT

As part of an ongoing investigation of the properties of dialkyl substituted diphosphonic acids as solvent extraction reagents for metal cations, we have studied the extraction of alkaline earth cations, Fe(III) and representative actinides (Am(III), U(VI) and Th(IV)) at tracer-level concentration by o-xylene solutions of P,P′-di(2-ethylhexyl) butanediphosphonic acid, H₂DEH[BuDP]. The extractant and acid dependencies of these metal ions exhibited significant differences from those of the previously investigated analogous extractants in which the two phosphonate groups are separated by a methylene or an ethylene bridge. The aggregation of H₂DEH[BuDP] was investigated in toluene at 25° C by vapor pressure osmometry. H₂DEH[BuDP] was found to exist predominantly as a trimeric species in the 0.1-0.005 molal concentration range. Osmometric measurements and infrared spectra indicate that Ca(II) is extracted into H₂DEH[BuDP] solutions with little disruption of the structure of the extractant. Iron(III) causes significant deprotonation of the ligand and dramatically changes the apparent aggregation number. A comparison of the extraction of Ca(II), Am(III) and Fe(III) by H₂DEH[BuDP] with data obtained using bis(2-ethylhexyl) phosphoric acid (HDEHP) or 2-ethylhexyl 2-ethylhexylphosphonic acid (HEH[EHP]) as the extractant indicates that H₂DEH[BuDP] has characteristics similar to these monofunctional analogs. Infrared spectra of the Ca(II) and Fe(III) salts of H₂DEH[BuDP] show a shift of both v_asym (POO?) and v_sym (POO?) to lower frequencies relative to their values in the sodium salt. This indicates a symmetrical interaction between the metal ion and the phosphonate groups through chelate and/or bridging interactions.     

TEMPERATURE EFFECTS IN THE EXTRACTION OF METAL IONS BY DIALKYL-SUBSTITUTED DIPHOSPHONIC ACIDS. I. THE Am(III) CASE

The extraction of Am(III) from HNO₃ by o-xylene solutions of P,P′-di(2-ethylhexyl) methylene- (H₂DEH[MDP]), ethylene- (H₂DEH[EDP]), and butylene- (H₂DEH[BuDP]) diphosphonic acids has been investigated. Thermodynamic parameters of the extraction process were determined by the temperature coefficient of the metal distribution ratio in the 25.0 to 60.0°C temperature range. The extractant aggregation and the extraction stoichiometries with the different diphosphonic acids did not exhibit any significant temperature dependence. Extraction of Am(III) by H₂DEH[MDP] is favored by both enthalpy and entropy variations. When Am(III) is extracted by either H₂DEH[EDP] or H₂DEH[BuDP] the process is entropy controlled. The enthalpy variation for Am(III) extraction exhibited a trend along the series H₂DEH[MDP], H₂DEH[EDP], H₂DEH [BuDP], with the reaction being exothermic for the first, thermoneutral for the second, and endothermic for the third extractant, respectively. This trend was explained as arising from the formation of progressively less stable chelate rings along the diphosphonic acids series. The zero or positive enthalpy variation with a concomitant favorable entropy variation confirm for H₂DEH[EDP] and possibly for H₂DEH[BuDP] a micellar-like type of extraction process.

     

SANS STUDY OF AGGREGATION OF THE COMPLEXES FORMED BY SELECTED METAL CATIONS AND P,P'-DI(2-ETHYLHEXYL) ETHANE- AND BUTANE-DIPHOSPHONIC ACIDS∗

ABSTRACT

The aggregation of several metal complexes formed during solvent extraction with P,P'-di(2-ethylhexyl) ethanediphosphonic acid, H₂DEH[EDP], and by P,P'-di(2-ethylhexyl) butanediphosphorac acid, H₂DEH[BuDP], in deuterated toluene, has been investigated by small angle neutron scattering (SANS). With H₂DEH[EDP], the extraction of Ca(II), La(IH) and U(VT) does not disrupt the cyclic hexameric structure of the ligand in solution. Fe(III) and Th(IV) complexes of H₂DEH[EDP], on the other hand, exhibit a very modest tendency to aggregate but only at very high metal loading in the organic phase. With H₂DEH[BuDP], the extraction of Ca(H), La(III), U(VI) and Th(IV) is not accompanied by significant aggregation of the metal complexes The Fe(HI)-H₂DEH[BuDP] complexes, however, form long cylindrical aggregates similar to those previously observed with P,P'di(2-ethylhexyl) methanediphosphonic acid, H₂DEH[MDP]. The aggregation behavior of the various metal-extractant species is discussed in light of the information obtained from earlier solvent extraction, vapor pressure osmometry, and infrared spectroscopy studies.     

HYDROGEN BONDING IN AGGREGATES OF DIALKYL-SUBSTITUTED DLPHOSPHONIC ACIDS AND MONOFUNCTIONAL ANALOGUES∗

ABSTRACT

Hydrogen bonding of dialkyl-substituted diphosphonic acids in nonpolar (toluene and CC1₄) and alcohol (1-decanol) solutions is examined. The compounds are monomeric in 1-decanol and dimeric or higher in nonpolar organic diluents. Infrared spectroscopy and molecular mechanics calculations suggest that the dimers of P,P'-di(2-ethylhexyl) methanediphosphonic acid (H₂DEH[MDP]) and its straight-chain isomer, P.P'-dioctyl methanediphosphonic acid (H₂DO[MDP]), adopt rigid highly hydrogen-bonded structures such as C or D. The homologous P.P'-di(2-ethylhexyl) ethane- and butanediphosphonic acids, H₂DEH[EDP] and H₂DEH[BuDP], respectively, adopt structures that are also intermolecularly hydrogen-bonded but more flexible. The effect on the P=0 stretching vibration of increasing 1-decanol concentration in the solvent differs for these compounds. In the case of H₂DEH[MDP]and H₂DO[MDP], the frequency remains constant until all CC1₄ has been replaced by the alcohol, then the P=0 stretching frequency shifts to a lower energy. In the case of H₂DEH[EDP] and H₂DEH[BuDP], a gradual shift to higher energy occurs as the alcohol concentration increases. The magnitude of the difference in the P=0     

ACIDS. PART 1. P,P"-DI(2-ETHYLHEXYL) METHANEDIPHOSPHONIC ACID

ABSTRACT

Two novel extractants, P,P'-di(2-ethylhexyl) methanediphosphonic acid (H2DEH[MDP]) and P.P'-dioctyl methanediphosphonic acid (H2DO[MDP]) have been synthesized at high purity and yield. H₂DEH[MDP] was selected for metal extraction studies because of its better physical properties. An investigation of the extraction of alkaline earth cations, Fe(III) and representative tri-, tetra- and hexavalent actinide ions from nitric acid solutions into o-xylene solutions of H₂DEH[MDP] at different concentrations was performed. With a few exceptions, the acid dependencies of the extraction of the above metal species strongly resembles those measured in the uptake of the same metals by the chelating ion exchange resin Diphonix®, which contains gem-diphosphonic acid groups chemically attached to a polymeric matrix. H₂DEH[MDP] exhibits practically no selectivity among the alkaline earth cations. The almost lack of acid dependency observed with Fe(lll) and tetra- and hexavalent actinides indicates that these ions are chelated by H₂DEH[MDP] mostly through the P=0 groups of the extractant. With Fe(lll) and the actinides, variable slopes of the extractant dependencies were measured, their values being strongly dependent on the acidity of the aqueous phase. Typically, the slope of the extractant dependency has a value of about two if the metal is extracted from high acidity solutions. This value becomes progressively lower as the aqueous acidity is reduced, tending to almost zero for acidities around 0.1 M. This phenomenon has been attributed to the formation of metal complexes having different stoichiometrics, ligand protonation and solubility in the aqueous phase.

H₂DEH[MDP] possesses an extraordinary affinity for actinides and Fe(III). In analogy with the Diphonix resin, this property can be exploited for actinide preconcentration and separation from complex matrices of analytical interest and from mixed waste solutions.     

EXTRACTION OF ALKALINE EARTH AND ACTINIDE CATIONS BY MIXTURES OF DI(2-ETHYLHEXYL) ALKYLENEDIPHOSPHONIC ACIDS AND NEUTRAL SYNERGISTS

ABSTRACT

The synergistic extraction of alkaline earth (Ca²⁺, Sr²⁺, Ba²⁺ and Ra²⁺) and actinide (Am³⁺, UO₂ ²⁺ and Th⁴⁺) cations from aqueous nitric acid solutions by mixtures of P,P^′-di(2-ethylhexyl) methylene-(H₂DEH[MDP]), ethylene-(H₂DEH[EDP]), and butylene-(H₂DEH[BuDP]) diphosphonic acids and neutral extractants in o-xylene has been investigated. The cis-syn-cis and cis-anti-cis stereoisomers of dicyclohexano-18-crown-6 (DCH18C6), the unsubstituted 21-crown-7 (21C7) and dicyclohexano-21-crown-7 (DCH21C7) were used as neutral synergists of the crown ether type. For Am(III) synergistic effects were also investigated using neutral organophosphorus esters, such as, tri-n-butylphosphate (TBP), diamyl amylphosphonate (DA[AP]) and tri-n-octylphosphine oxide (TOPO) as co-extractants. In all systems investigated, no synergistic extraction enhancement was observed for actinide ions. For the alkaline earth cations, synergistic effects were only observed when mixtures of H₂DEH[EDP] or H₂DEH-[BuDP] with DCH18C6 were used to extract Sr²⁺, Ba²⁺ and Ra²⁺. No synergistic effects were observed for the extraction of alkaline earth cations by H₂DEH[MDP] or for the extraction of Ca²⁺ by any of the diphosphonic acids studied. The synergistic effects obtained with DCH18C6 were significantly higher for the cis-syn-cis than for the cis-anti-cis stereoisomer.     

AGGREGATION OF COMPLEXES FORMED IN THE EXTRACTION OF SELECTED METAL CATIONS BY P,P'-DI(2-ETHYLHEXYL) METHANEDIPHOSPHONIC ACID*

ABSTRACT

The aggregation of several metal complexes formed during solvent extraction with P,P'-di(2-ethylhexyl) methanediphosphonic acid, H₂DEH[MDP], in deuterated toluene, has been investigated by small angle neutron scattering (SANS). The SANS results show that the Ca(II)-, Al(ni)-, La(III)- and Nd(III)-H₂DEH[MDP] compounds exhibit little or no tendency to aggregate. Uranyl complexes of H₂DEH[MDP] at high metal loading form small aggregates with an aggregation number of approximately 14. This behavior is in sharp contrast with the Th(IV)-H₂DEH[MDP] system which forms large aggregates in the organic phase under high metal loading conditions. The aggregation behavior of the various metal-H₂DEH[MDP] compounds is discussed in light of the information obtained from earlier solvent extraction, vapor pressure osmometry, and infrared spectroscopy studies.     

Selected Alkyl(phenyl)-N,N-dialkylcarbamoylmethylphosphine Oxides as Extractants for Am(III) from Nitric Acid Media

Abstract

A new series of neutral bifunctional extractants, alkyl(phenyl)-N,N-dialkylcarbamoylmethylphosphine oxides, has been prepared and studied as extractants for Am(III) from nitric acid media. Two types of alkyl(phenyl)-N,N-dialkyl CMPO compounds were prepared, one containing N,N-diethyl groups and the other containing N,N-diisobutyl groups. The N,N-diethyl series contained hexyl(phenyl) and 6-methylheptyl(phenyl) derivatives, abbreviated HφDECMPO, and 6-MHφDECMPO, respectively. The N,N-diisobutyl series contained the n-octyl(phenyl), 6-methylheptyl(phenyl), and the 2-ethylhexyl(phenyl) derivatives, abbreviated OφD[IB]CMPO, 6-MHφD[IB]CMPO, and 2-EHφD[IB]CMPO, respectively. Third power extractant dependencies for the extraction of Am(III) from 0.5 and 3 M HNO₃ were obtained at low (<0.25 M) concentrations of extractant, but higher power dependencies were obtained above 0.25 M extractant from 3 M HNO₃. The HφDECMPO, 6-MHφDECMPO, 6-MHφD[IB]CMPO, and OφD[IB]CMPO [all 0.5 M in diethylbenzene (DEB)] are significantly better extractants than DHDECMPO for Am(III) from 1 to 6 M HNO₃. These same extractants have lower D _Am values than DHDECMPO at low acidities. HφDECMPO and OφD[IB]CMPO also have better selectivity for Am(III) over Fe(III) than DHDECMPO. HφDECMPO in DEB has a strong tendency toward the formation of a second liquid organic phase on extracting macroconcentrations of Nd(III) and U(VI) from 3 M HNO₃; however, this behavior is substantially diminished with the OφD[IB]CMPO and 6-MHφD[IB]CMPO compounds.     

Synthesis and Evaluation of N,N′-dimethyl-N,N′-dicyclohexyl-Malonamide (DMDCMA) as an Extractant for Actinides

A malonamide based extractant, i.e., N,N′-dimethyl-N,N′-dicyclohexyl-malonamide (DMDCMA) was synthesized in a single step and tested for the extraction of several actinide ions such as Am(III), U(VI), Np(IV), Np(VI), Pu(IV), Pu(VI), etc., from nitric acid medium. The extractant was soluble in phenyltrifluoromethylsulphone (PTMS or FS-13) unless stated otherwise. The effect of various experimental parameters, such as the aqueous phase acidity (0.01–3 M HNO₃), nature of the acid, oxidation states of the metal ions, ligand concentration, nature of the diluent and temperature on the extraction behavior of metal ions was studied. The extracted Am(III) species was determined from slope analysis method as [Am(NO₃)₃(DMDCMA)₂]. The extraction of the metal ions was found to increase with the aqueous phase acidity. The temperature variation studies allowed the calculation of the heat of the two-phase extraction reaction as well as the corresponding extraction constants. These studies revealed that DMDCMA showed good extraction for all the actinide metal ions investigated, and have the advantage of single stage synthesis and easier purification protocol.     

AGGREGATION OF P,P' -DI( 2-ETHYLHEXYL) METHANEDIPHOSPHONIC ACID AND ITS Fe(III) COMPLEXES ∗

ABSTRACT

The aggregation of P,P' -di( 2-ethylhexyl) methanediphosphonic acid, H2DEH[ MDP] dissolved in deuterated toluene has been investigated by small angle neutron scattering ( SANS) The title compound was shown to exist in solution as a dimer under all conditions. Dimer formation is independent of the acidity of the aqueous solution with which the organic solution is pre-equilibrated. Solutions of H₂ DEH[ MDP] containing increasing amounts of Fe( lll) extracted from aqueous solutions in the acidity range from 0.1 to 5 M were also investigated. The SANS results confirm the tendency of H2DEH[ MDP] -Fe( III) species in aromatic diluents to form rod-like aggregates characteristic by a constant cross section and a length which increases with increasing amounts of metal in the organic phase. Particle growth is independent of the acidity of the aqueous solutions from which the metal is extracted. These results are important for understanding the chemistry underlying the solvent extraction behavior H₂DEH[ MDP] and its practical application in separation procedures.     

UPTAKE OF METAL IONS BY A NEW CHELATING ION-EXCHANGE RESIN. PART 5 : THE EFFECT OF SOLUTION MATRIX ON ACTINIDES

ABSTRACT

The influence of commonly occurring matrix constituents on the uptake of representative actinides in the tri-, tetra-, and hexavalent oxidation states by a new chelating ion exchange resin, called Diphonix?, has been investigated. The effect of increasing concentrations of HF at three fixed HC1 concentrations on the retention of U(VI), Np(IV), and Am(III) was measured. All three actinides showed strong retention in HF even up to a concentration of 1 M The effect of sulfuric, oxalic and phosphoric acids at three fixed HNO₃ concentrations on the retention of Th(IV), U(VI), and Am(III) was also measured. Only when the concentration of the complexing acids was above 0.1 M was the retention of the actinides decreased significantly at 0.1 M HNO₃ The effect was much less pronounced at higher HNO₃ concentrations.

Sodium, calcium, aluminum and iron were selected to study the influence of cationic matrix constituents on the uptake of actinide ions by Diphonix. In the case of tetra- and hexavalent actinides (represented by Th and U, respectively) only the very highest concentrations of Fe(III) and Al(III) caused a significant decrease in the retention of the two higher valent actinides. On the other hand, Am(III) retention was significantly lowered by Al and Fe(III) concentrations above 10^?2 M The influence of Al and Fe(III) on the uptake of Am(III) may be minimized by use of fluoride ion to complex Al and by reducing Fe(III) to Fe(II). Macroconcentrations of sodium and calcium had only minimal influence on the uptake of actinides in all three oxidation states.     

Studies on the Extraction of Actinides Using a Solvent Containing D2EHiBA in Room Temperature Ionic Liquids: Unusual Extraction of the Tetravalent Ions

The extraction behavior of U(VI), Pu(IV), and Np(IV) from nitric acid medium has been studied using branched chain di(2-ethylhexyl)isobutyramide (D2EHiBA) dissolved in different room temperature ionic liquids (RTILs) [C_nmim][NTf₂] (where n = 4, 6, or 8). Uranium extraction (D_U) increased gradually with aqueous phase acidity for the three RTILs used in this study suggesting solvation mechanism. There was a reversal in the extraction behavior of Pu(IV) and Np(IV) from nitric acid medium using D2EHiBA dissolved in RTILs as solvents as compared to the behavior reported in the molecular diluent, n-dodecane, which shows negligible extraction of these metal ions. The extraction of Pu(IV) increased with aqueous phase acidity in different RTILs in the order: [C₈mim][NTf₂] > [C₆mim][NTf₂] > [C₄mim][NTf₂]. The distribution ratio values of these metal ions followed the order: D_Pu(IV) ≥ D_Np(IV) > D_U(VI) using D2EHiBA as extractant suggesting that RTILs can modify the extraction behavior of extractants.     

Solvent Extraction Separation of Some Actinides and Lanthanides with 2-Thenoyltifluoroacetone

Abstract

Solvent extraction behavior of Th(IV) and U(VI) and some lanthanides [Ce(III), Nd(III), Eu(III), Tb(III), and Yb(III)] from thiocyanate medium into sulfoxides and/or 2-thenoyltrifluoroacetone has been studied. The actinides are found to be favorably extracted by both the extractants. The alkyl sulfoxides extract Th(IV) and U(VI) as Th(SCN)₄·3DPSO, Th(SCN)₄·3DOSO, UO₂ (SCN)₂·2DPSO, and UO₂(SCN)₂·3DOSO. The chelate extracts the metals in the following order: U(VI) < Th(IV) < Eu(IV) < Tb(III) < Tb(III) < Ce (III) or Nd(III).     

Separation of U(VI) and Th(IV) from Nd(III) by Cross-Current Solvent Extraction Mode Using Tri-iso-amyl Phosphate as the Extractant

Separation of U(VI) and Th(IV) from Nd(III) in nitric acid media with solutions of tri-iso-amyl phosphate (TiAP) in n-dodecane has been studied by batch extraction in cross-current mode to evaluate the feasibility of employing TiAP as an alternate extractant to tri-n-butyl phosphate (TBP) for monazite ore processing. The interference of U(VI), Th(IV), and Nd(III) in the presence of each other during their analyses by titrations has also been validated in the present study. The extraction studies substantiate that the high solvent loading conditions can be achieved without organic phase splitting in the extraction from concentrated feed solutions with TiAP based solvents, whereas TBP forms third phase under such conditions. The separation factor for Th(IV) with respect to Nd(III) can be improved with TiAP as the extractant and by carrying out the extraction with feed solution in 8 M HNO₃. Solvent extraction studies conducted with solutions of U(VI), Th(IV), and Nd(III) in nitric acid media by TBP and TiAP revealed the identical extraction, scrubbing, and stripping behavior of both the extractants with respect to U(VI), Th(IV), and Nd(III). The results insinuate that TiAP can be used as an alternate extractant to TBP for the separation of U(VI) and Th(IV) from monazite ores. The data generated in the present study can be exploited for the development of flow sheets using TiAP based solvents to separate U(VI) and Th(IV) from rare earths for the processing of monazite leach solutions.     

EXTRACTION BY N,N'-TETRAALKYLMALONAMIDES II.

Suitable N.N'-tetraalkylmalonamldes for Am(III) extraction from concentrated HNO₃ aqueous liquors have been selected. Extraction mechanisms of Eu(III) and Am(III) by NN'-dlmethyldioctylmalonamide (DMDOMA) have been investigated. The distributions ratios of Am(III) and Eu(III) between 1M DMDOMA in t-butylbenzene and per chloric acid are higher than those obtained In nitrate media. Extraction data for Pu)IV), U(VI), Fe(III), Zr(IV) are reported. From these results It can be concluded that the NN'-dlmethyldlal-kylmalonamldes are good extractants for the actinides contained in the radioactive wastes.     

Distribution Studies of Actinides Using a Tetradentate Extractant, 4,4′-Nonanedioyl-Bis(2,4-Dihydro-5-Methyl-2-Phenyl-3H-Pyrazol-3-One)

Abstract

The extraction of Th(IV), UO₂(II), Am(III), and Eu(III) from aqueous acid by a tetradentate extractant, 4,4′-nonanedioyl-bis(2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one), H₂NDBP, has been studied and compared with two bidentate model compounds, 4-hexanoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one, HHMPP, and 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one, HBMPP. The distribution coefficients of UO₂(II), Am(III), and Eu(III) were somewhat larger using H₂NDBP relative to the model compounds under the conditions studied. However, the Th(IV) extraction using H₂NDBP was greatly enhanced when compared to HBMPP or HHMPP. The distribution coefficient for Th(IV) from 0.5 M HNO₃ was 11.6 using 3.0 × 10^?3 M H₂NDBP compared with values of D < 0.01 using 3.0 × 10^?3 M HBMPP or HHMPP.     

Extraction of U(VI), Th(IV), and Lanthanides(III) from Nitric Acid Solutions with CMPO-Functionalized Ionic Liquid in Molecular Diluents

The extraction of microquantities of U(VI), Th(IV), and lanthanides(III) from nitric acid solutions with CMPO-functionalized ionic liquid 1-[3[[(diphenylphosphinyl)acetyl]amino]propyl]-3-tetradecyl-1H-imidazol-3-ium hexafluorophosphate, CMPO-FIL(I) in molecular organic diluents has been studied. The effect of HNO₃ concentration in the aqueous phase and that of extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes was determined. CMPO-FIL(I) demonstrates greater extraction ability towards Ln(III) than its neutral CMPO analog, diphenylphosphorylacetic acid N-nonylamide. This inner synergistic effect increases with a decreasing organic diluent polarity. The partition of CMPO-FIL(I) between the equilibrium organic and aqueous phases is the dominant factor governing the extractability of Ln(III) ions in the extraction system.     

Radiolytic Stability of N,N,N′,N′-Tetraoctyl Diglycolamide (TODGA) in the Presence of Phase Modifiers Dissolved in n-Dodecane

The radiolytic stability of a promising extractant for actinide partitioning from high-level radioactive liquid waste, namely N,N,N',N'-tetraoctyl diglycolamide (TODGA) was investigated in the presence of several phase modifiers, viz. N,N-dihexyloctanamide (DHOA), tri-n-butyl phosphate (TBP), 1-decanol, and iso-decanol dissolved in n-dodecane. The distribution ratio of Am(III) decreased with increased radiation dose studied up to 1000 kGy. Nevertheless, all the compositions of extractants showed fairly high extraction of Am(III) up to 500 kGy (D_Am: ≥ 50), beyond which significant decrease was observed. However, the D_Am values were sufficiently high for process applications for the chosen compositions even at an absorbed dose of 1000 kGy. The stripping behavior of Am(III) with 0.2 M HNO₃ was found to be favorable with increased absorbed dose by the solvent up to 1000 kGy. With an increased absorbed dose, the loading of Nd(III) in the organic phase decreased due to depletion of ligand/extractant concentration (TODGA) in the organic phase. There was marginal variation in the hydrodynamic parameters such as density, viscosity, and interfacial tension (IFT) of the irradiated solvents vis-a-vis fresh/unirradiated solvent.     

EXTRACTION OF ACTINIDES AND SELECTED FISSION PRODUCTS FROM NITRIC ACID MEDIUM USING LONG CHAIN MONOAMIDES

A series of long chain disubstituted aliphatic amides have been prepared with different substituting groups and the extracting ability for U(VI), Th(IV) and some fission products like Am(III), Zr(IV), Eu(III) and Cs from nitric acid solutions has been studied. All results were compared with those obtained by using TBP under the same conditions. All prepared amides exhibit higher U-Th separation factors than TBP. Distribution ratios of U(VI) as function of nitric acid concentration, extractants concentration and salting-out agent have been measured by using N,N-dihexyloctanamide (DHOA) and N,N-dihexyl(2-ethyl)hexylhexanamide (DHEHA), which were chosen for further studies. The extraction behviour of U(VI), Th(IV) and Zr(IV) with gamma irradiated DHOA, DHEHA and TBP in toluene from 3 M HNO₃ has been studied as a function of absorbed doses. Back extraction of U(VI), Th(IV) and Zr(IV) from organic phases was also studied.     

Study of Uranium Removal from Groundwater by Supported Liquid Membranes

The separation of uranium from synthetic Hanford site groundwater by liquid-liquid extraction and by supported liquid membranes (SLM) was atudied. Bis(2,4,4-trimethylpentyl) phosphinic acid, H[DTMPeP], contained in the commercial extractant Cysnex 272, was selected for the membrane carrier because of its selectivity for uranium over calcium and magnesium. n-Dodecane was used as diluent and polypropylene membranea were used as the support. A water soluble complexing agent, 1-hydroxyethane-1,1-diphoaphonic acid, HEDPA, was used as atrlpping agent.

The permeability coefficient of U(V1) was evaluated from a detailed study of the permeation of U(VI) through flat-sheet SLMs as a function of the membrane carrier concentration. The diffusion coefficient of the uranium complex in the organic phase was also evaluated from permeation experiments performed under loading conditions. Experiments were also carried out with Cs(II) and Fe(III) to measure the membrane selectivity for U(VI) over these two cations. A very high selectivity of U(VI) over Cs(II) was obtained, due the very low distribution ratio of Cs(II) with the extractant H[DTMPeP] (thermodynamic selectivity). In the case of Fe(III), a good selectivity was also obtained, due to the slow reaction of Fe(III) species with H[DTMPeP] (kinetic selectivity).

The possibility of concentrating U(VI) in the strip solution by a factor of at least 10³ has been experimentally demonstrated by properly designed distribution experiments.