[en] This paper reports the interest of the novel 4-carboxyphenyl-grafted screen-printed electrodes (4-CP-SPEs) for sub-nano-molar analysis of uranium in water samples. Electrodes were easily prepared via electrochemically reduction of the corresponding diazonium salt. The stability of the grafted layer has been clearly demonstrated. Uranium detection was then achieved by immersing the grafted electrode into the sample solution, followed by the electrochemical measurement of adsorbed U(VI) by square wave voltammetry. Adsorption time was investigated so as to find the best compromise between analysis time, repeatability and reproducibility. Limit of detection and quantitation reached 7 * 10^-10 and 2 * 10^-9 mol L^-1 respectively. Moreover, interference study was conducted with Zn(II), Cd(II), Pb(II) and Cu(II); no major interference was established. 4-CP-SPEs were finally applied for uranium determination in estuarine water demonstrating the convenience of these electrodes for environmental analysis. (authors)

[en] The safety of radioactive wastes disposal requires a big knowledge on their aging facing a corrosive environment. The corrosion is a complex phenomenon which implies many processes bound to the physic and the chemistry of the system. This approach proposes, from a little number of simple processes, numerical simulation which will define theses complex phenomenon. The presented model is a 2 dimension model at a mesoscopic scale and based on cellular automates. It allows the simulation of a metal evolution, protected by a polymer layer and in contact at one point with a corrosive media at a defect of the layer. (A.L.B.)

[en] The normal potential of the Ce(IV)/Ce(III) redox couple was determined by square wave voltammetry (SWV) at different temperatures in solutions with a constant ratio [CO₃^2-]/[HCO₃^-] approximate to 10 for high ionic strengths (3.29 mol dm^-3 at 4.39 mol dm^-3): E_IV/III⁰' varies from 259.5 to 198.0 mV/S.H.E. in the 15-50 degrees C range. Linear variations were found for E_IV/III⁰ versus (RT/F)In(m(CO₃^2-)), leading, to the stoichiometry, Ce(CO₃)₆^8- for the Ce(IV) limiting complex. But the slopes of these linear variations were actually found in the range 1.8-1.9, not exactly 2. This was interpreted as dissociation of the Ce(IV) limiting complex following the reaction: Ce(CO₃)₅^6- + CO₃^2- → Ce(CO₃)₆^8- and as dissociation of the Ce(III) limiting complex following the reaction: Ce(CO₃)₃^3- + CO₃^2- → Ce(CO₃)₄^5-: for which maximum possible values of log(10) K-IV,K-6 and log(10)K(III.4) were estimated via fitting in the 15-50 degrees C temperature range (log(10) K_IV,6 = 0.42 (0.97) and log(10) K_III,4 = 0.88 (7.00) at 15 degrees C (50 degrees C). The normal potential was found to decrease linearly with T, these variations correspond to T⁰Δ_rS_T⁰ approximate to -46 kJ mol^-1, with T-0 = 298.15 K and Δ_rH_T⁰ approximate to 70 kJ mol^-1. The apparent diffusion coefficient of Ce(IV) was determined by direct current polarography (DCP), cyclic voltammetry (CV) and square wave voltammetry. It was found to depend on the ionic strength and to be proportional to T. (authors)

[en] This work deals with the electrodeposition of manganese compounds. A systematic study of the synthesis experimental conditions has been carried out, and the obtained depositions have been characterized by different ex-situ analyses methods (XRD, FTIR, SEM). The in-situ measurements of mass increase with a quartz microbalance during the syntheses have allowed to estimate the growth mechanisms which are in agreement with the ex-situ characterizations. The cation has an important role in the nature of the electrodeposited compounds. In presence of sodium, a mixed lamellar compound Mn(III)/Mn(IV), the birnessite, is deposited, whereas in presence of potassium, bixbyite is formed (Mn₂O₃), these two compounds having a main role in the environment. The substrate can also influence the nature of the formed intermediary compounds. Little studied compounds such as feitkneichtite (β-MnOOH) and groutite (α-MnOOH) have been revealed. (O.M.)

[en] The electrophoretic mobilities (μ_ep,Ln) of twelve lanthanides (not Ce, Pr and Yb) were measured by CE-ICP-MS in 0.15 and 0.5 mol L^-1 Alk₂CO₃ aqueous solutions for Alk⁺ = Li⁺, Na⁺, K⁺ and Cs⁺. In 0.5 mol L^-1 solutions, two different μ_ep,Ln values were found for the light (La to Nd) and the heavy (Dy to Tm) lanthanides, which suggests two different stoichiometries for the carbonate limiting complexes. These results are consistent with a solubility study that attests the Ln(CO₃)₃^3- and Ln(CO₃)₄^5- stoichiometries for the heavy (small) and the light (big) lanthanides, respectively. The Alk⁺ counter-ions influence the μ_ep,Ln^Alk2CO3 values, but not the overall shape of the μ_ep,Ln^Alk2CO3 plots as a function of the lanthanide atomic numbers: the counter-ions do not modify the stoichiometries of the inner sphere complexes. The influence of the Alk⁺ counter-ions decreases in the Li⁺ ≥ Na⁺ ≥≥ K⁺ ≥ Cs⁺ series. The K_3,Ln stepwise formation constants of the Ln(CO₃)₃^3- complexes slightly increase with the atomic numbers of the lanthanides while K_4,Ln, the stepwise formation constants of Ln(CO₃)₄^5- complexes, slightly decrease from La to Th, and is no longer measurable for heavier lanthanides. (authors)

[en] In the framework of studies concerning the uranium migration in soils and rocks, it seems necessary to quantify the uranium(VI) dissolved in solution. In the environmental conditions, the uranium(VI) is present at trace amounts. The most adapted method to this study and easy to carry out is the Adsorptive Stripping Voltammetry. By addition of a compound (ligand) with a reducing and strong complexing power, the uranium(VI) present in solution is reduced into a U(VI)-ligand complex. This specie is then oxidized and adsorbed on the mercury droplet where an electrolytic pre-concentration of the element to determine the quantity of is carried out. At last, a cathodic re-dissolution of the specie adsorbed in the U(IV)-ligand complex is carried out. The chosen analytical method is the differential impulsional voltammetry. With this method, it is possible to quantify low electro-active species quantities (sensitivity ∼25 ppt (10^-10 mol.L^-1) for the uranium). This titration method in solution has been optimized, at first, in a non complexing medium. Then, the uranium in solution has been titrated in media whose composition has been progressively complexed (additions of CO₃^2-, SO₄^2-, Cl^-..) for being at last representative of the environmental interstitial waters. At last, this study has been carried out too by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) in order to compare the analysis sensitivity of these two detection methods. (O.M.)

[en] In order to assess the security of a long-term disposal of nuclear spent fuel, the prediction of radionuclide migration is needed. This paper presents the interaction between uranium(VI) and siderite surfaces, an iron carbonate present both in the near- and far-field of the storage, in carbonate solutions. The amount of uranium on the surface was determined after the interaction by alpha spectrometry. It appeared that the amount of uranium(VI) dropped with high pH and carbonate concentration, likely because of the predominance of UO₂(CO₃)₂^2- and UO₂(CO₃)₃^4- complexes in solution. The U4f X-ray photoelectron spectrum clearly highlighted that uranium present on the film has two different oxidation states and thus that uranium(VI) has been partially reduced by siderite. (orig.)

[en] In the context of long-term nuclear waste management, understanding the migration of a major component of spent fuel, uranium namely, in the environment is of major importance. This study presents the kinetics of uranium(VI) retention and reduction in carbonate solutions by siderite, an iron carbonate present both in the near- and far-field. At pH 9, uranium(VI) is retained at the surface, reduced and then precipitated into UO_2.67. At pH 7, uranium(VI) seems, first, to be incorporated into iron precipitates at the solid/liquid interface and, subsequently, reduced by the Fe(II) contained in the thin layer. (orig.)

[en] Cerium is the only non radioactive element of the f series for which the oxido-reduction reactions between its oxidation degrees three or four, are enough fast to be able to study the corresponding equilibria by different electrochemical techniques. The best results are obtained here by square wave voltametry (SWV) technique on a static mercury drop electrode (SMDE). The differential peak current (ΔI_p) and the peak potential (E_p) of volt-amperometric waves obtained by SWV have respectively allowed the determination of the apparent diffusion coefficient of Ce(IV)(D_IV) and of the apparent normal coefficient of the couple Ce(IV/III)(E⁰'). These two electrochemical constants have been calculated in Na₂CO₃/NaHCO₃ medium of high ionic strength (3.29 mol.L^-1 at 4.39 mol.L^-1 and neutralized [CO₃^2-][HCO₃^-]∼10. The potential E⁰' has been obtained after correction of the effects of the activity coefficients and of the junction potential, the influence of the carbonate concentration (of 1.06 to 1.45 mol.L^-1) reveals the exchange of two carbonate ions (slope of about 2RT/F by unit of ln[CO₃^2-]) between the limit complexes of Ce(IV) and Ce(III), which confirms the stoichiometries: Ce(III)(CO₃)₄^5- and Ce(IV)(CO₃)₆^8-. A light deviation of the slope of the curve E⁰' in terms of [CO₃^2-] is interpreted as an occurrence of the partial dissociation of Ce(IV)(CO₃)₆^8-. It has been possible to deduce Log10K₆^IV=0.42(0.97) at 15 C (50 C). The influence of the temperature on E⁰' has allowed to determine T⁰ Δ_rS ∼- 50 kJ.mol^-1 and Δ_rH ∼-70 kJ.mol^-1 at T⁰=298.15 K. The enthalpic and entropic contributions are then of the same order of value. This study enters into the general framework of the researches aiming at acquiring thermodynamic data to model the behaviour of radionuclides near a disposal or eventual storage of wastes. (O.M.)

[en] A combination of simple processes that may be assumed to be present in a large class of corrosion phenomena taking place in natural environment conditions are described. A heterogeneous chemical reaction coupled with a diffusion reaction process and a precipitation phenomenon is considered, and a simple model for describing a non-uniform corrosion probability introduced. Although extremely simple processes are retained the numerical simulations lead to a large number of types of behaviour. In particular, it is possible to investigate the transition from general to localised corrosion. The model may predict the existence of pseudo-cyclic evolution in the structure of the corrosion front. (authors)