Summary The substitution of the Cl - ions of TcCl 6 2- in various media (Cl - , SO 4 2- , TFMS - ) at various pH or the electroreduction of TcO 4 - in the same media led to a common Tc(IV) species characterized by an UV-visible absorption band at 500nm. This band was present in the spectra of Tc(IV) in all the media investigated, except in chloride at low pH. The analysis of the spectroscopic data showed that it can be attributed to a Tc(IV) oxopolymeric species.The data fits better with a trimeric species Tc 3 O 4 4+ which reminds the Mo 3 O 4 ·9H 2 O 4+ clusters known for Mo(IV). The stability of 3×10 -5 M Tc 3 O 4 4+ solutions has been investigated as a function of pH with respect to the formation of Cl - complexes at low pH, and precipitation of TcO 2 at pH, higher than 3. The anions of the media interact with Tc 3 O 4 4+ clusters as shown by small changes in their UV-visible spectra. We observed that the affinity of Tc 3 O 4 4+ for these ions is in the order: SO 4 2- >Cl - >TFMS - . Neutral species Tc 3 O 4 (SO 4 ) 2 are observed in 0.1M sulphate solutions.

Summary X-ray absorption spectroscopy has been used to establish polymer formation of Tc(IV) in aqueous solutions of Na+SO42− and Na+Cl−/SO42−. As the molybdenum chemistry show similarities to that of technetium, we used MoO2 as a reference to model our technetium species. Fitting of TcO2·xH2O with this model led to a good correlation with the literature data: (Tc-Tc=2.53 Å, Tc-O=1.87-1.98 Å). In aqueous solution, some polymers are formed regardless to the nature of the media composition: Tc-Tc=2.50 ± 0.02 Å. The general structure is in agreement with a first coordination shell containing 6 O. The modelling shows that, in the first coordination shell, there is no chloride ligand. The observed geometries are close to those found for TcO2·xH2O, hence the unknown aqueous species must be considered as a precursor of the solid technetium dioxide. Combination of these results with XANES led to attribute TcnIVOp(4n-2p)+(H2O)q with n>2 to the species.

The speciation of tetravalent technetium has been studied in HCl solutions ranging from 1.0 to 6.0 M. Tc(IV) exists in 6.0 M HCl as the well characterized TcCl62-chloride complex. In 1.0 M HCl, the chloride ligands of TcCl62-are slowly substituted by other ligands such as H2O, OH-or O2-. So TcClmOn(OH)p(H2O)q(4-m-2n-p)+compounds may form with (m + n + p + q) = 6. Several speciation techniques such as UV-visible and Raman spectrometries, X-ray absorption spectroscopy and electrochemistry have enabled to get an insight into this problem. All the results have indicated two most likely species of Tc(IV) after aging for about ten days in 1.0 M HCl to be aquo-chlorocomplexes of technetium and not oxo-chorocomplexes: TcCl5· H2O-and TcCl4· 2 H2O.

Aqueous carbonate complexes of Mn-II, Mn-III and Mn-IV were prepared and investigated by UV-visible spectrophotometry and electrochemical techniques. Mn-II forms soluble anionic carbonate complexes in concentrated carbonate solutions. A complex with two CO32- has been found in 1 M K-2 CO3 solutions. The value of its conditional formation constant is in the range 10(5.7 +/- 0.3). The soluble Mn-II carbonate complexes are readily oxidized by air to Mn-III species. Mn-IV complexes were obtained by reduction of MnO4- ions or by oxidation of Mn-II in concentrated carbonate solutions. Insoluble solids, probably oxides, were often produced during the studied oxidation-reduction reactions.

The properties of the extractants suitable for the new types of separations needed in the nuclear fuel cycle are reviewed. N,N-dialkylamides (RCO-NR(2)'), diamides ((RR'NCO)(2) CHR "), N,N-dialkylcarbamoylmethylenephosphonates (R(2)NCOCH(2)PO (OR')(2)) or N,N-dialkylcarbamoylmethylene phosphines oxides (R(2)NCOCH(2)POR(2)'), trialkylphosphine oxides (R(3)PO); soft donors ligands for the trivalent actinide-lanthanide group separation are considered. The reasons for development of these separations are: 1) the separation of actinide (III, IV, VI) from high level waste (SPIN or OMEGA programs) or actinides separation for waste decomissioning; 2) the replacement of TBP by N,N-dialkylamides in new PUREX reprocessing plants; the interest of N,N-dialkylamides for spent Th fuel reprocessing will also be discussed; 3) the actinide (III)-lanthanide(III) group separations needed before nuclear incineration of the long half life actinides.

The extraction properties of N,N-diethyldodecanamide in hydrochloric and nitric acid solutions for uranium, plutonium, thorium and americium have been investigated. As a primary step, the liquid scintillation performances of organic solutions of the amide have been studied revealing a moderate quenching and a lower energy resolution than HDEHP. Nitric acid, uranyl nitrate and thorium nitrate extraction systems have been modeled, taking into account the stoichiometric mean activity coefficients in aqueous solutions. A general protocol to analyse actinides (U, Th, Pu and Am) in soils in conjunction with liquid scintillation counting is proposed using this amide together with other extractants (TOPO, HDEHP).

A new approach to the determination of the standard potential E-0 of a redox couple involving Tc(VII) based on the reduction of technetium by ferrous iron is presented. Formal potentials E'(0) were estimated in 1.0 M HCl media at different technetium concentrations to be higher than 0.8 V: the redox couple does not refer to TcO4-/TcO2(solid) but to TcO4- in equilibrium with an other Tc(IV) species.

New commercial liquid scintillation counters allow rapid α/β measurements. Associated with liquid-liquid extraction techniques, rapid and selective actinide analyses are possible. Uranium, thorium and americium extractions with tri-n-octylphosphine oxide (TOPO) in toluene have been investigated. Detection limits of 40 mBq·l−1 for α-emitters are currently obtained with a Packard 2550 TR/ABTM liquid scintillation analyzer.

Abstract In the framework of the SPIN(ACTINEX) program for the partitioning and transmutation of actinides contained in effluents generated during the nuclear fuel reprocessing cycle, diamides and picolinamides, extractants which have the common characteristic of being totally combustible, were evaluated. Among the diamides, N,N-dimethyl N,N-dibutyl tetradecyl malonarmide (DMDBTDMA) was chosen as the reference extractant. It has been shown that actinides(III) may be extracted from concentrated nitric acid effluent; the actinides(III) may be readily stripped from the loaded solvent. There is restricted third-phase formation. Long alkyl groups (R″) and different R and R' on the amide nitrogen limit the extent of third-phase formation. The second class of extractants studied, the picolinamides, seem to have potential for the separation of An(III)/Ln(III).

Extraction equilibria of U(VI) and Pu(IV) between aqueous nitric acid solutions and the diamide DMDBTDMA ((C4H9(CH3)NCO)2CHC14H29) dissolved TPH were investigated. Extraction takes place via the formation of L.UO2(NO3)2, L.Pu(NO3)4 and L2.Pu(NO3)4 for all the acidities. Bilogarithmic dependencies of distribution coefficients on the ligand concentration reveal non-integer slopes higher than those expected from saturation. Such features, very often observed for amides, can be explained by outer sphere coordination. Thus, two kinds of interactions were observed : - in the inner sphere of the metal : diamide-metal ion complexation; - in the outer sphere of the metal : diamide-metallic complex interactions.

The extracting properties of substituted diamides were investigated. The auto-association of N,N'-dimethyl dibutyl tetradecyl malonamide (DMDBTDMA) : (C4H9(CH3)NCO)2CHC14H29 in benzene and in TPH (aliphatic hydrocarbon) was shown by NMR using mass-action model. The degree of aggregation depends on the diluent, the diamide concentration and the acidity. The extraction of HNO3 and HClO4 was investigated by distribution measurements and IR spectroscopy. HNO3 extraction is explained by the competing formation of four adducts : L2.HNO3, L.HNO3, L.(HNO3)2, L.(HNO3)3 whose the equilibrium constants for 0,72 mol.l-1 amide in TPH are 0.167 , 0.215 , 5.19.10(-3) and 3.7.10(-4), respectively, on a molal scale. HClO4 is extracted by a reaction involving the competing formation of the two adducts L2.HClO4 and L.HClO4. Their equilibrium constants for 0.697 mol.l-1 amide in TPH are 0.649 and 1.71, respectively, on a molal scale. Nu(C=O) IR absorption shifts indicate that in L2.HNO3 and in L.HNO3, DMDBTDMA and HNO3 are linked by hydrogen bonds, whereas in L.(HNO3)2, L.(HNO3), and in L.HClO4 one H+ is transferred from one molecule of acid to one C=O of the DMDBTDMA. The different behavior of HClO4 and HNO3 can be attributed to their different acid strength, HClO4 being a much stronger acid than HNO3. The proton transfer from HNO3 to the diamide depends on the dielectric constant of the organic medium, the higher values being favourable to ion-pair formation. Oxalic acid is only weakly extracted by DMDBTDMA.

The non-ideality of multicomponent media are difficult to describe, especially for situations as complex as the extraction of metals into organic media.We present a simplified model which takes into account 'hard-sphere' effects and physical interactions between some solutes of the studied media in the case of actinide ions liquid-liquid extraction. We focus our interest on N,N-dialkylamides extractants which have a strong non-ideal behaviour.

Pyrometallurgical processes for the purification of plutonium for defense create waste solutions containing actinides, mainly americium, in chloride medium. Studies have been undertaken to study the extraction of actinides in a chloride medium (hydrochloric acid mixed with concentrated salts such as LiCl, CaCl2, MgCl2, KCl) using pentaalkylpropanediamides as extractants. Plutonium(IV) is very easily extracted, but Am(III) needs a salting-out agent such as LiCl. Back extraction of trivalent cations is easy in HCI <5 M. Plutonium(IV) and (VI) can be stripped by reduction either with ascorbic acid M hydroxylammonium salts in a weak-acid medium. Several diluents can be used (aromatic, chlorinated, or even aliphatic) with addition of decanol to prevent third-phase formation. In conclusion, diamides can be used for declassification of various wastes, they are potentially completely incinerable, and, as the synthesis has been optimized, they appear to be promising extractants.

Substituted propanediamides were studied at Fontenay-aux-Roses for the declassification of nuclear liquid wastes by extraction of all the actinides. Their synthesis has been improved. By optimization of the formula, it is possible to use aliphatic diluents without third-phase formation in contact with nitric acid at 20-degrees-C. Addition of oxalic acid allows separation of iron and zirconium from americium and plutonium. In selected conditions, it appears that americium extraction is faster than iron extraction, which could lead to practical applications. Recent studies have shown that diamides can be used to remove the actinides from waste solutions in chloride medium coming from defense facilities. The current knowledge and the projects for using diamides as actinide extractants will be reviewed.

N,N-dialkylamides are potential alternative extractants to tributylphosphate for the actinide separation in nuclear fuel reprocessing.Extraction mechanisms of U(VI), Th(IV) and Pu(IV) from nitric acid media are investigated for the amide DOBA(((C4H9) (C2H5) CHCH2)2 NC(O) C3H7) and DO(i)BA (((C4H9) (C2H5) CHCH2)2 NC(O) CH(CH3)2).For low aqueous acidities, amides are neutral extractants. Extraction stoichiometries of UO2(NO3)2(Amide)2 (Amide = DOBA or DO(i)BA), Pu(NO3)4(DOBA)2 have been established. Th(IV) is supposed to form a di- and a trisolvate in the inner-coordination sphere. For concentrated solvents, bilogarithmic dependences of distribution coefficients with ligand concentration point out non-integer slopes higher than those expected from stoichiometry. Such features, very often noted for amides, do not seem to be due to new chemical second-sphere species, which has never observed experimentally, but to polyoriented interactions between free ligands and complexes and may be considered as part of non-ideality.Amides behave as anionic extractants with increasing acidity. New species are formed, involving UO2(NO3)3- and Pu(NO3)6(2-) anions, with the protonated amide ligands in the outer-coordination sphere of metals.

PURPOSE: To selectively extract actinide in an organic solvent by adding thiocyanate to an aqueous nitric solution and by contacting the solution with the organic solvent containing a specific propane diamide. CONSTITUTION: When actinide is separated from lanthanide in the aqueous nitric solution, thiocyanate is added first into the solution and next the organic solvent containing propane diamide shown by a following equation is brought into contact with the solution by using a pulse column. In the equation, R 1 and R 2 are each an alkyl group of 1-15C or -(CH 2 ) n -Z-(CH 2 ) m -O-R 4 , where R 4 is alkyl group of 1-6C, n and m and 1-6, Z is a single bond or an oxygen atom, R 3 is hydrogen, alkyl group of 1-25C, or -(CH 2 ) n -Z-(CH 2 ) m -OR 4 . According to the method, actinides can be recovered in high yield. COPYRIGHT: (C)1993,JPO