Natural sintering of carbonate powder for use as a carbon-14 immobilization matrix

International audienc

Remediation of 137^{137}Cs-contaminated concrete gravels by supercritical CO2_2 extraction

International audienceThe removal of cesium contamination is a critical issue for the recycling of concrete gravel in most decommissioning sites . The high solvent strength and diffusivity of supercritical CO$_2$ make it an attractive choice as vector for extractant system in this context. Experimental extraction runs have been carried out in a radioactive environment on gravels contaminated with $^{137}$Cs. The best extraction system was found to be CalixOctyl (25,27-Bis(1-octyloxy)calix(4)arene-crown-6, 1,3-alternate) with pentadecafluorooctanoic acid as a modifier. The effects of various operating parameters were investigated, namely the coarseness of the gravel, the temperature of SC-CO$_2$, the residual water and initial cesium concentrations, and the amounts of extractant and modifier used. The yields from direct extraction were low (< 30percent), because of the virtually irreversible sorption of Cs in concrete. The best extraction yield of $\sim$55percent was achieved by leaching the concrete gravel with nitric acid prior to supercritical CO$_2$ extraction

The effect of pore diameter in the arrangement of chelating species grafted onto silica surfaces with application to uranium extraction

International audienc

Effect of composition on ionic transport in SiO2-B2O3-Na2O glasses

International audienceIonic diffusion was investigated in the SiO2B2O3Na2O glass system over a wide composition range by impedance spectroscopy measurements. The Na+ cation transport mechanism was described by an interstitial pair migration model based on Frenkel defects in ionic crystals. The activation energy of the static electrical conductivity is shown to be correlated with the boron coordination number in these glasses. Published 11B NMR results were used to calculate the activation energies of sodium cations acting as charge compensators for the (BO4-2)- tetrahedron and of sodium cations bonded to nonbridging oxygen atoms . These values are in agreement with the activation energies of the Na2OB2O3 and Na2OSiO2 binary systems, respectively

Effects of Impregnated Amidophosphonate Ligand Concentration on the Uranium Extraction Behavior of Mesoporous Silica

A series of solid-phase uranium extractants were prepared by post-synthesis impregnation of a mesoporous silica support previously functionalized with octyl chains by direct silanization. Five materials were synthesized with 0, 0.2, 0.3, 0.4 and 0.5 mmol of the amidophosphonate ligand DEHCEBP per gram of functionalized solid, and the effect of the ligand concentration on the uranium extraction efficiency and selectivity of the materials was investigated. Nitrogen adsorption&ndash;desorption data show that with increasing ligand loadings, the specific surface area and average pore volume decrease as the amidophosphonate ligand fills first the micropores and then the mesopores of the support. Acidic uranium solutions with a high sulfate content were used to replicate the conditions in ore treatment leaching solutions. Considering the extraction kinetics, the equilibration time was found to increase with the ligand concentration, which can be explained by the clogging of micropores and the multilayer arrangement of the DEHCEBP molecules in the materials with their highest ligand contents. The fact that the equilibrium ligand/uranium ratio is about 2 mol/mol regardless of the ligand concentration in the material suggests that all the ligand molecules remain accessible for extraction. The maximum uranium extraction capacities ranged from 30 mg&#8729;g&minus;1 at 0.2 mmol&#8729;g&minus;1 DEHCEBP to 54 mg&#8729;g&minus;1 in the material with 0.5 mmol&#8729;g&minus;1 DEHCEBP. These materials could therefore potentially be used as solid-phase uranium extractants in acidic solutions with high sulfate concentrations

Solubility and solution enthalpy of a cesium-selective calixarene in supercritical carbon dioxide

International audienceThis paper investigates the solubility of the cesium-selective extractant 25,27-Bis(1-octyloxy)calix[4]arene-crown-6, 1,3-alternate (CalixOctyl) in supercritical CO$_2$ (SC-CO$_2$). A dynamic setup with a solvent loop was used, avoiding any plugging of the solute and allowing precise quantification by UV/visible spectrophotometry. The solubility measurements were carried out between 10.3 and 27.4 MPa at 314, 324 and 334 K. The solubility of CalixOctyl in SC-CO$_2$ ranged from (0.20 $\pm$ 0.02)·10$^{−6}$ mol·mol$^{−1}$ at 334 K and 10.4 MPa to (72.78 $\pm$ 0.31)·10$^{−6}$ mol·mol$^{−1}$ at 324 K and 27.4 MPa, approximately 100 times higher than that of simple $p-t$-butylcalix[4,6,8]arenes and calix[4]arene. The solution enthalpy of CalixOctyl in SC-CO$_2$ was also studied. The heat flow during solubilization at 24.0 MPa and 314, 324 and 334 K was measured by differential scanning calorimetry. The temperature dependence of the solution enthalpy and its extrapolation to any pressure are discussed

Solubility of Perfluoropentanoic Acid in Supercritical Carbon Dioxide: Measurements and Modeling

International audienceThe solubility of perfluoropentanoic acid in supercritical carbon dioxide was investigated for a broad range of pressures (10 to 26 MPa) and at three temperatures: 314, 324, and 334 K. A dynamic gravimetric device was used for the high pressure measurements. The solubility ranges from (24.7 +/- 0.3) kg.m(-3) at 334 K to 10.2 MPa to (103.9 +/- 7.7) kg.m(-3) at 314 K and 20.1 MPa. Density-based models, notably the dimensionless version of the Adachi-Lu model, fit the experimental data accurately. The latter model was employed to calculate the solubility over a wide range of CO2 densities

Tuning the thermal stability of copper(II) hexacyanoferrate(II)

International audienceWhile it is well recorded that the family of transition metal hexacyanoferrates efficiently, and selectively, extract Cs ions from what should be highly competitive environments, the why of this efficiency is still somewhat unclear. In this work Potassium-Copper (II) Hexacyanoferrate (II), before and after, Cs/K exchange was examined using a number of spectroscopic techniques including solid UV-Vis, FT-IR, TGA, Elemental Analysis, XRD, EXAFs and PDF. Definite long range and local structure changes were observed when Cs was introduced into the Cu-HCF system. Gathering these various spectral observations together we propose a possible Cs sorption mechanism for Cu-HCF in which a type of Jahn-Teller distortion (common within copper complexes) is removed as the Cs is selectively sorped. These spectral changes were not observed when the K+ guest ions were exchanged for H+ ions, adding credence to our believe that the changes are unique to Cs exchange

Monolithic zirconia foams synthesis from emulsion stabilized by colloidal clusters

International audienc

Simultaneous lanthanides and surfactants micelles removal from aqueous outflows by complexation and sol–gel chemistry

International audienc