[en] In the field of environmental control, the behavior of plutonium in various media and particularly in surface waters is relevant taking into account its radiotoxicity. Carbonate ions widely present in these media mainly complex pentavalent plutonium. In this field, CE-ICP-MS coupling, which was already used for actinides speciation, has been considered for the determination of thermodynamic constants associated to plutonium carbonate complexes. The study developed on plutonium (VI) allowed determining the stability constants at 25 C. From these values, the specific interaction coefficients based on the values recommended by the NEA have been reevaluated. The speciation diagram of Pu(VI) in aqueous carbonate solution has been established and shows the complexation of the plutonyl form by carbonates complex beyond pH=3. The works realized on the complexation of actinides (V) (Np and Pu) by carbonate ions at different temperatures allowed determining both the stability constants and the molar enthalpies and entropies of reaction. Experimentally, the analogy between neptunium and plutonium has been observed and allowed the determination of values which are more precise and consistent with those of the literature. For a better understanding of the plutonium behavior in surface waters, the determination of enthalpies and entropies has been necessary. The speciation diagrams established from these values show a near similarity in the chemical distribution of plutonium species without any further consideration of the analyzed surface water location. (author)

[en] the identity of the limiting Pu(IV) species under high carbonate concentrations has been determined to be Pu(CO₃)₅^6-. Single crystals of [Na₆Pu(CO)₃₅]₂ · Na₂CO₃ · 33H₂O were obtained from a 0.15 M solution of Pu(IV) in 2.6M Na₂CO₃. The asymmetric unit contains a complex network consisting of [Pu(CO₃)₅]^6- anions and Na⁺ cations which are linked through interactions with CO₃^2- and H₂O ligands. Each Na⁺ ion is coordinated to the O atoms of H₂O or CO₃^2- ligands such that the Na⁺ ions achieve either octahedral or square-based pyramidal coordination. The [Pu(CO₃)₅]^6- anions can be viewed as a pseudohexagonal bipyramid with three CO₃^2- ligands in a equatorial plane and two in axial positions. EXAFS data for Pu(IV) in 2.5M Na₂CO₃ solution were collected at the Pu L_III edge. Curve fitting reveals three shells in the FT spectrum. The UV-vis diffuse reflectance spectrum of a single crystal of [Na₆Pu(CO)₃₅]₂ · Na₂CO₃ · 33H₂O ground into a powder is nearly identical to the solution absorption spectrum of the limiting Pu(IV) carbonato complex in 2.5 M Na₂CO₃ solution. The peak by peak correspondence by position and relative absorption strengths, along with solution EXAFS data, suggest that the Pu(IV) chromophore is the same in both cases, and confirms that the [Pu(CO₃)₅]^6- ions is the limiting species in high carbonate solutions. Crystal data for [Na₆Pu(CO₃)₅]₂ · Na₂CO₃ ·-33H₂O are given

[en] The development of actinide speciation methods in the environment is discussed. The results on speciation and migration of radionuclides in near-surface and deep conditions at the Krasnoyarsk mining and chemical plant and at the Production Association 'Mayak' (southern Ural) are reported. For surface conditions, the mobile plutonium fraction is mostly associated with inorganic complexes (carbonate) of the higher plutonium oxidation state, while less mobile fraction is associated with low-soluble Pu(IV) complexes with humic acids. The mobile fraction of americium consists of complexes with low molecular weight fulvic acids of non-specific nature with molecular weights lower than 10 kDa. Plutonium and americium behaviour in deep conditions is governed by colloid migration. (authors)

No abstract available

[en] Pulsed-laser photoacoustic spectroscopy (PAS) and Fourier-transform nuclear magnetic resonance (NMR) spectroscopy were used to study speciation of actinide(IV) and actinide(VI) ions (Np, Pu, Am) in aqueous carbonate solutions vs of pH, carbonate concentration, actinide content, and temperature. PAS focused on Pu(IV) speciation. Stability fields on a pH (8.4 to 12.0) versus total carbonate content (0.003 to 1.0 M) plot for dilute Pu(IV) carbonate species ([Pu]_tot = 1 mM) were mapped. Four plutonium species, with absorption peaks at 486, 492, 500, and 512 nm were found. Loss of a single carbonate ligand does not account for the difference in speciation for the 486 and 492 nm absorption peaks, nor can any of the observed species be identified as colloidal Pu(IV). NMR data have been obtained for UO₂²⁺, PuO₂²⁺ and AmO₂²⁺. This report focuses on results for PuO₂²⁺. The ligand exchange reaction between free and coordinated carbonate on the PuO₂(CO₃)₃^4- systems has been examined by variable temperature ¹³C NMR spectroscopy. In each of the six different PuO₂(CO₃)₃^4- samples, two NMR signals are present, one for the free carbonate ligand and one for the carbonate ligand coordinated to a paramagnetic plutonium metal center. The single¹³C resonance line for coordinated carbonate is consistent with expectations of a monomeric PuO₂(CO₃)₃^4- species in solution. A modified Carr-Purcell-Meiboom-Gill NMR pulse sequence was used for determining of ligand exchange parameters for paramagnetic actinide complexes. Eyring analysis at standard conditions provided activation parameters of ΔH = 38 KJ/M and ΔS = -60 J/K for the plutonyl triscarbonate system, suggesting an associative transition state for the plutonyl(VI) carbonate complex self-exc

[en] Absorption spectra of Pu(IV) in carbonate/bicarbonate media have been examined between pH=8.8 and 10.6. The Pu(IV) is prepared by oxidation of electrochemically produced Pu(III). Measurements for solutions with lower Pu concentrations down to pH 8.2 are carried out by laser induced photoacoustic spectroscopy (LPAS). Quantitative analysis of the spectra by multiple regression indicates the presence of three Pu(IV) species, that can be assumed as Pu(CO₃)₃^2-, Pu(CO₃)₄^4-, and Pu(CO₃)₅^6-. (orig.)

[en] Ethylenediaminetetraacetic acid (EDTA) is a potentially significant agent for enhancing the mobility of plutonium and other actinides in the environment, however the existing literature data may not be valid at environmentally relevant pH values (pH 5--8). The authors are studying the EDTA complexation of plutonium(IV) to: confirm/refute existing literature data; determine if EDTA can compete with carbonate ions (such that plutonium(IV) carbonate complexation constants could be derived); and determine the potential for actinide migration at mixed-waste contaminated sites. Preliminary experiments have produced spectra of the EDTA-plutonium(IV) complex at pH 8.4 which, when carbonate is added, show significant spectral changes suggesting that a mixed EDTA-plutonium(IV)-carbonate complex is present which has not previously been reported. A brief review of the literature is presented followed by discussion of the results of experiments in progress

[en] Solubility of Pu(IV) was measured over a total carbonate concentration range of 10^-4 to 10^-1 M at room temperature (20-25 C) and I=0.1. Since carbonate was not detected in the solid phase, the solubility controlling solid was assumed to be a hydrous oxide, PuO₂.χH₂O. A limit of the equilibrium constant of the exchange reaction between PuO₂.χH₂O and a carbonate solid phase, PuOCO₃.χH₂O, was estimated as: PuO₂.χH₂O+CO₃^2-+H₂O=PuOCO₃.χH₂O+2OH^-K<10^-6.7. The measured solubility was proportional to the square of the bicarbonate concentration at the pH range of 9.4-10.1. This result was interpreted by PuO₂.χH₂O+2HCO₃^-=P(OH)₂(CO₃)₃^2-+χH₂OK=10^-2.7±0.5 At pHs 12 and 13 where carbonate ion is dominant, PuO₂.χH₂O+2CO₃^-2=Pu(OH)₄(CO₃)₂^4-+(χ-2)H₂OK=10^-4.98±0.31 is the predominant reaction. (orig.)

[en] Carried out is X-ray investigation of the crystal structure of the compounds M₃AnO₂(CO₃)₂xnH₂O(1) and Msub(4)AnOsub(2)(COsub(3))sub(2,5)xnHsub(2)O(2), where M=Na, K and Rb, An=Np(5), Pu(5) and Am(5). Determined is a general structural scheme of carbonate compounds of pentavalent actinides, in the basis of which is mutual substitution of actinide atoms and atoms of alkaline metals. It is shown, that the main structural elements of different carbonate compounds are anion layers of [Msub(x)(AnOsub(2))sub(1-x)COsub(3)] variable composition, where x can have the values from 0 to 1. It is shown, that as far as the structure is concerned, the compounds (1) and (2) are recorded in the form of Msub(2)[MAnOsub(2)(COsub(3))sub(2)]xnHsub(2)O(1) Msub(2)[Msub(1,2)(AnOsub(2))sub(0.8)x(COsub(3))sub(2)]xnHsub(2)O(2) and they are the edge members of the continuous lin of Msub(2)[Msub(1+x)(AnOsub(2))sub(1-x)(COsub(3))sub(2)]xnHsub(2)O compounds, where 0 < or approximately X < or approximately 0.2. On the basis of the obtained peculiarity of carbonate crystal structure considered is the possibility of corbonate compounds formation of different composition

[en] Published in summary form only