SummaryX-ray absorption spectroscopy has been used to establish polymer formation of Tc(IV) in aqueous solutions of NaAs the molybdenum chemistry show similarities to that of technetium, we used MoOIn 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 TcOCombination of these results with XANES led to attribute Tc

Pyrite (FeS2) is a mineral phase often present as inclusions in temperate soils. Moreover, it turns out to be a sorption sink for certain radionuclides in deep geological disposals. The present study was thus initiated to determine the capacity of pyrite to immobilize selenide (Se(-II)). Due to the fact that pyrite surface oxidizes readily, potentials were applied in order to minimise its surface evolution, and ensure the reducing conditions necessary for stabilizing Se(-II). The sorption experiments were carried out in NaCl electrolyte and were amperometrically controlled. After only several minutes of reaction, at least 97% of Se(-II) initially present in solution was disappeared. The Kd values vary from 7–65 L/g and the isotherm curve shows site saturation at higher initial selenide concentrations and no pH-dependence. By means of several spectroscopic techniques, the reaction mechanism was investigated. The XRD and in situ XANES results indicate the presence of Se(0) on pyrite surface, which explain the rapid disappearance of Se observed in the sorption experiments. Moreover, XPS results obtained from Se-reacted pyrite particles reveal cleavage of S–S bonding which resulted in formation of S2− on pyrite surface. Thus, we conclude that Se(-II) can be immobilized by pyrite via surface redox reaction: ≡FeS2 + HSe− ⇔ ≡FeS + Se(0) + HS−

Iodide sorption experiments were conducted on clay stone samples originating from the Callovian-Oxfordian formation under experimental conditions as close as possible to in situ conditions. The total natural iodine content of the formation is shown to be very constant throughout the formation, ranging from 2 to 3 ppm. This range is in agreement with a past iodine accumulation in the marine organic matter of the sediment before and during deposition, and early diagenesis. At variance with total iodine, the leached iodine concentrations are variable. If leached iodine is considered to represent porewater solute iodine, its concentration can be calculated and ranges from 0 (below detection limit) to ~60 µmol/L and represents 0 to 25 % of the total iodine. The reason for this variability is not understood. Sorption isotherms were determined either for natural 127 Isolutions or for 131 Ispiked 127 Isolutions, with concentrations ranging from 10-9 to 10-3 mol/L at solid to liquid ratios from 10 to 200 g/L. No or little sorption was encountered, Kd values being in the range 0-0.5 L/kg with statistical and analytical error bands being greater than the Kd values, with the exception of one experiment at low solid to liquid ratio (10 g/L), showing significant Kd values of ~25 L/kg. In sorption experiments with natural 127 Iand at the lowest added iodide concentrations (< 10-6 mol/L) an apparent negative Kd was obtained due to the iodide content in the solid porewater that was leached once the solid was suspended. The low affinity of iodide for argilite is thus confirmed. However, based only on these results and given the extent of the error bands, one cannot discard a limited iodide uptake. Literature data on iodide diffusion on similar rock materials have already shown that iodide does not behave like chloride. The retention mechanism of radio-iodide is discussed in the light of the present results and diffusion data. A model involving isotopic exchange between the natural iodine content of the geological formation and radio-iodine allows all of the results to be described. 2 Not all the iodine in the formation appears to participate in isotopic exchange reactions with the solution. A quantification of the isotopically labile fraction of iodine would allow the effect of isotopic exchange on radio-iodide migration throughout the Callovian-Oxfordian formation to be assessed and predicted.

The yields of the radiolytic oxidation of U(IV) and of the U(VI) formation, measured by spectrophotometry, are found to be the same (G(-U(IV))(N2O) = G(U(VI))(N2O) = 8.4 x 10(-7) mol J(-1)) and almost double the H(2) formation yield (G(H(2)) = 4.4 x 10(-7) mol J(-1)) in the (60)Co gamma radiolysis of N(2)O-aqueous solutions in the presence of 2 mol L(-1) Cl(-) at pH = 0 (HCl). According to the mechanism of U(IV) radiolytic oxidation, we show that under the conditions of our experiments the U(V) ions do not disproportionate, but undergo a stoichiometric oxidation into U(VI) by H(+) with forming H(2).