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Comparison of defect-controlled leaching-kinetics modulation of metal-organic frameworks (MOFs) and porous functionalized silica-based materials was performed on the example of a radionuclide and radionuclide surrogate for the first time, revealing an unprecedented readsorption phenomenon. On a series of zirconium-based MOFs as model systems, we demonstrated the ability to capture and retain99% of the transuranic

The extraction of cerium from cotton substrate, as a matrix model, using supercritical CO2 modified with phosphorus extractant and co-solvent/water in wise proportions, has been investigated. Using a recently developed isobutyl amidophosphonate extractant, the aim of this study was to emphasize how besides the usually considered operating parameters (flow rate, pressure and temperature), the efficiency of supercritical CO2 extraction of cerium depends on the concentration of cerium nitrate deposits on the substrate (between 0.27 and 261 mg gcotton−1) and on the presence and composition of co-solvent/water mixture as well. The variations of the extraction efficiency with the nature of the Ce nitrate deposits (aggregates or homogenous layers) are explained by using a deposition model confirmed using SEM and coupled with SAXS data. Extraction is promoted when Ce nitrates deposits are in the form of segregated aggregates instead of homogeneous layers. Phase equilibrium data for CO2-ethanol-amidophosphonate and CO2-isopropanol-amidophosphonate ternary systems have been measured at 40 °C and 25 MPa to investigate the benefit of using a co-solvent. Extraction experiments show that adding a co-solvent and carefully adjusting the water concentration up to 30%wt are crucial to obtain high mass extraction yields, here up to 82%.

In the development of a conditioning process for cesium-bearing sorbents from the decontamination of aqueous waste streams, the treatment of a granular material composed of (Cs,K)2CuFe(CN)6 loaded onto mesoporous silica particles has been investigated in an additive-free two-step conditioning process involving (i) calcination at 1000 °C to remove volatile species and (ii) densification by spark plasma sintering. A 92.0 % dense pellet was obtained after 10 min sintering at 850 °C under 100 MPa. Density and microstructural measurements indicate that densification is first driven by the viscous flow of a vitreous phase containing Cs, formed during calcination. The density of the sample then increases further during sintering by grain boundary diffusion. However, a limited but non negligible part of cesium is lost during densification.

Ferrocyanides with general formulaAIxBIIy[Fe(CN)6], whereAandBare cations, are thought to accept many substitutions on theAandBpositions. In this communication, the synthesis and crystal structure of Cs2Sr[Fe(CN)6] are reported. The latter was obtained from K2Ba[Fe(CN)6] particles, put in contact with caesium and strontium ions. Hence, a simultaneous ion-exchange mechanism (Cs for K, Sr for Ba) occurs to yield Cs2Sr[Fe(CN)6]. The synthesis protocol shows that K2BaFe(CN)6particles can be used for the simultaneous trapping of radioactive caesium and strontium nuclides in water streams. Cs2Sr[Fe(CN)6] adopts the cryolite structure type and is isotypic with the known compound Cs2Na[Mn(CN)6] [dicaesium sodium hexacyanidomanganate(III)]. The octahedrally coordinated Sr and Fe sites both are located on inversion centres, and the eightfold-coordinated Cs site on a general position.

It is well known that the physical properties of nanoparticles can be tuned by controlling synthetic factors such as pH, temperature, reactant ratio or type of stabiliser used. In this work, the reactant ratio is varied to produce batches of copper(II) hexacyanoferrate(II) (Cu-HCF) with different cyano decomposition temperatures. This is accomplished by controlling the number of Fe(CN) 6 4− site vacancies throughout the structure. By reducing the number of vacancies and consequently the need for water to complete the structure, the thermal decomposition temperature of Cu-HCF can be increased. In addition to this, we also note that the guest ion similarly contributes to the decomposition temperature. By exchanging K+ with Cs+, an increased resistance to thermal decomposition is realised. As the incorporation of Cs+ ions into the structure does not alter the number of Fe(CN) 6 4− site vacancies, this enhancement is attributed to a change in the geometry of the copper coordination sphere.

International audience; Radioactive 137Cs is one of the most common and problematic radionuclides in nuclear wastes. Decontamination typically involves passing the waste in continuous flow through an agitated or fixed bed reactor containing an efficient sorbent. There are many articles in the literature describing a broad spectrum of highly efficient sorbents. However, comparing their properties is often difficult, mainly because the experimental conditions used differ. We describe the series of experiments that need to be performed to characterize Cs sorbents and illustrate by comparing three of these that, for the extraction of trace elements, the kinetics and selectivity of the exchange process are far more important than the maximum extraction capacity of the material.

A green solvent-free approach, using a heating/grinding method, was employed to produce grey colored Ag functionalized mesoporous silica (here SBA-15). This material consisted of Ag0 nanoparticles with diameters of around 1.5 ± 0.45 nm inside the pores of SBA-15, and aggregated silver nanoparticles on the outside of the SiO2. Indeed due to a lack of a strong stabilizer the degree of particle aggregation is high. This easy to handle powder was then used to extract molecular Iodine. The resulting yellow powder was examined by Ultraviolet–Visible (UV–Vis) and Fourier-transform Infrared spectroscopies, X-rays diffraction, thermogravimetric analysis (TGA) and scanning and transmission electron microscopy (SEM/TEM). It was found that the aggregates of individual Ag nanoparticles disaggregate as AgI quantum dots are formed, explaining the high I2 capacity exhibited by these materials, almost 1:1 Ag to I. Despite numerous washing steps with a range of solvents (ranging from cyclohexane to water) no leaching was observed. Finally, TGA demonstrated an increased melting point for the AgI dots indicating a degree of protection from the silica support.

Multiscale, hierarchical, porous materials are promising nuclear wasteform materials with potential for efficiently adsorbing and sequestering radionuclides. However, fundamental understanding of such complex micro- and meso-structures on radionuclide diffusion and uptake kinetics is lacking, which is essential for designing advanced nuclear wasteform materials. In this work we develop a microstructural-dependent diffusion model that accounts for three-dimensional (3D) microstructural features, including heterogeneous thermodynamic and kinetic properties, to predict radionuclide uptake kinetics in complex porous structures. Na+ and Sr2+ ionic exchange in LTA zeolite multiscale materials in batch tests is taken as a model system to demonstrate the model and its application to hierarchical materials with multiscale porosity. It is found that the reduction of ionic mobility associated with chemistry, structure, and/or phase changes has more profound impact on the uptake kinetics in a large 3D porous particle than that in a small one. Uptake kinetics in large particles are limited by two diffusion processes: bulk diffusion and surface layer transport. Decreasing particle size and increasing mesoscale pore volume fraction changes the uptake kinetics from two diffusion processes to a single process and dramatically increases the uptake kinetics. Predicted uptake kinetics and the effect of microstructures on the effective capacity of radionuclides and uptake efficiency are consistent with results observed in Na+/Sr2+ exchange experiments. The results demonstrate that the developed model should be adaptable to transport problems in other hierarchical material systems.

International audience; Silica monoliths loaded with hexacyanoferrate (HCF) nanoparticles were designed and synthesized to selectively remove Cs+ ions from an aqueous saline solution within a continuous flow set-up. The decontamination and hydrodynamic efficiency of this smart material was compared to other granularly supported HCF. Finally, a thermal treatment was applied to transform the HCF functionalized monolith into a final waste form matrix.

Vacuumable gels have been developed in the nuclear industry to decontaminate solid surfaces with little or no mechanical operations and without producing any liquid effluents. These gels can be spread on the contaminated surface and rapidly trap the radio-contaminants by sorption after corroding the substrate down to several tens of microns if necessary. The gel then dries and eventually fractures into a non-powdery solid that is easily removable by brushing or vacuum cleaning. This process was initially developed for the nuclear decontamination of metallic surfaces but innovative formulations are being developed for wide range of applications. This paper introduces two such formulations designed to remove sticky organic layers, bitumen in this study. We show that adding an organic bio-solvent, limonene, allows bitumen layers to be dissolved, absorbed in the liquid state into the gel matrix, and then removed from the substrate as solid waste after drying. Substituting an organic co-solvent (ethanol) for some of the limonene improves the overall efficiency of the process by decreasing the drying time of the gel and limiting the diffusion of the dissolved bitumen without affecting the dissolving power of the gel. Finally, the performance of these gels is demonstrated for the removal of nuclear contaminated (137Cs) bitumen stains.

International audience; Xanthan gum is used to stabilize aqueous foams in a wide number of commercial and industrial processes and is one of the numerous hydrosoluble polymers used to slow foam drainage. The slowing effects of viscosity on drainage flow have been well studied but the situations leading to a drainage delay are poorly described in the literature. The aim of this study was to shed light on the mechanisms governing drainage delay and drainage initiation. Drainage delay seems to be the result of liquid retention caused by the confinement of xanthan molecules in the Plateau borders, which increases local yield stress. Drainage begins when the bubbles and Plateau borders grow above a certain threshold size that allows liquid to flow through the foam.

International audience; Removal of brominated flame retardants (BFRs) from polymers before disposal or recycling will alleviate negative environmental effects and ensure safe usage of recycled products. Extraction of BFRs in supercritical CO$_2$ is appealing but also presents challenges to industries due to limited solubility and lack of kinetic studies. For a more comprehensive evaluation of supercritical extraction potentialities, we (i) developed an on-line pressure apparatus that is compatible with both the FTIR and UV-vis spectrometers to enable kinetic and thermodynamic studies; (ii) studied kinetic extraction involving three conventional and two novel BFRs as well as three typical polymeric matrix. Solubilities were determined using the gravimetric method or X-ray fluorescence. FTIR exhibited a superior applicability compared to UV-vis in the following BFR extraction’s time-dependency binary and ternary systems. We observed that faster stirring speed, higher temperature, and finer particle size can accelerate the overall extraction kinetics. In binary systems, it took less than 2 hours to achieve equilibrium for each BFR at 60 °C, 25 MPa and 1000 rpm. In the presence of polymeric matrix, slower extraction kinetics were observed due to the occurrence of competitive dissolution and molecular diffusion within the matrix. Mathematical models derived from irreversible desorption and Fick’s diffusion laws fitted well with the observed extraction kinetics of BFRs, thus enabling us to identify the rate-determining step. The high solubilization rate coefficients that we measured for BFRs revealed that the dynamic extraction process in up-scaling design could compensate for the low solubility with flowing supercritical CO$_2$.

Plastics in waste electronics (E-plastics) account for approximately 20% of the entire global electronic waste (E-waste) stream. Most of the E-plastics are not recycled as the presence of toxic additives (e.g. heavy metals, brominated flame retardants (BFRs), antimony, etc.) have associated environmental and health concerns. However, the majority of the studies are focused on quantitative assessment of the toxic constituents in E-plastics, while empirical information regarding the potential toxic effects in humans is largely lacking. To gain a deeper appreciation into the toxicological profile of E-plastics, in situ time-dependent exposures of 6 different human cell lines to a panel of 8 representative E-plastics recovered from liquid crystal displays (LCD), keyboards, screen frames, and wire insulators were conducted. Although several hazardous elements (e.g. Pb, As, Sb, Zn, Cu, etc) were detected at concentrations that far exceed the limit values permitted by the Restriction of Hazardous Substances Directive and EU Directives in the panel E-plastics, in-depth analysis of the 144 unique cell viability data points and live-dead staining experiments suggest that the acute and sub-chronic toxic effects of E-plastics in direct contact with human cells are negligible. These observations agreed with the inductively coupled plasma-optical emission spectrometry data, which revealed that leaching of these toxic additives into the biological milieu is not sufficiently high to trigger a cytotoxic response up to a continuous culture period of 2 weeks. The novel insights gained from this study are posited to further clarify the uncertainty associated with the safety and circular economy implementation of E-plastics. Ministry of National Development (MND) Nanyang Technological University National Environmental Agency (NEA) National Research Foundation (NRF) This work was financially supported by a grant award from “Singapore eCEA Alliance for Research in Circular Economy (SCARCE)”, which is a joint lab set up between Nanyang Technological University (NTU, Singapore) and the French Alternative Energies and Atomic Energy Commission (CEA, France). SCARCE is supported by the National Research Foundation, Prime Minister’s Office, Singapore, the Ministry of National Development, Singapore, and National Environment Agency, Ministry of the Environment and Water Resource, Singapore under the Closing the Waste Loop R&D Initiative as part of the Urban Solutions & Sustainability e Integration Fund (award number USS-IF-2018-4).

Cs2Sr[Fe(CN)6] was synthesized. It is a potential phase to trap simultaneously caesium and strontium radionuclides. The crystal structure is isotypic with Cs2Sr[Mn(CN)6]., Ferrocyanides with general formula A I xB II y[Fe(CN)6], where A and B are cations, are thought to accept many substitutions on the A and B positions. In this communication, the synthesis and crystal structure of Cs2Sr[Fe(CN)6] are reported. The latter was obtained from K2Ba[Fe(CN)6] particles, put in contact with caesium and strontium ions. Hence, a simultaneous ion-exchange mechanism (Cs for K, Sr for Ba) occurs to yield Cs2Sr[Fe(CN)6]. The synthesis protocol shows that K2BaFe(CN)6 particles can be used for the simultaneous trapping of radioactive caesium and strontium nuclides in water streams. Cs2Sr[Fe(CN)6] adopts the cryolite structure type and is isotypic with the known compound Cs2Na[Mn(CN)6] [dicaesium sodium hexa­cyanidomanganate(III)]. The octa­hedrally coordinated Sr and Fe sites both are located on inversion centres, and the eightfold-coordinated Cs site on a general position.

A new route for the synthesis of silver-phosphate based sorbent beads as precursors of final iodine waste form is proposed here. This sorbent is used to entrap gaseous iodine produced during the reprocessing of spent nuclear fuels and to be directly transformed into materials composed of a silver phosphate glass phase considered as high efficient iodine containment matrix for long-term storage in deep geological repository. Using sacrificial organic template method (alginate) and well controlled calcination of the obtained silver phosphate grains materials, this innovative synthesis makes in-situ formation of metallic silver inside them. Ag0 then can easily entrap iodine when in contact with gaseous iodine. The obtained sorbent were tested for iodine trapping in static conditions. They showed great performances with a catch rate of 480 mg.g−1. The iodine-loaded sorbent were finally heat treated at 650 °C with an iodine loss lower than 3% wt. The resulted materials shows the presence of the expected silver phosphate glass matrix with a great iodine incorporation of 9% mol.

The delamination of photovoltaic modules with supercritical CO2 is an interesting approach to integrate photovoltaics into a circular economy. This article describes the first phase of this process: the absorption of CO2 into poly(ethylene-co-vinyl acetate) (EVA-28), one of the layers in a photovoltaic module. The swelling of the polymer, determined by an on-line coupling between high pressure cell and an optical method using digital camera, under 60–200 bar at 60, 75 and 90 °C, was well reproduced by a modified Sanchez-Lacombe equation of state. The diffusion coefficient of CO2 into EVA-28 was determined using the same approach and was found to range, at 130 bar, from 1.1 × 10−9 m2·s−1 at 60 °C to 1.8 × 10−9 m2·s−1 at 90 °C. A preferential CO2 diffusion at the rear side of the cell, due to a high porosity, and at the “backsheet” interface was highlighted.

The removal of cesium contamination is a critical issue for the recycling of concrete rubble in most decommissioning operations. The high solvent strength and diffusivity of supercritical CO2 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 rubble contaminated with 137Cs. 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 rubble, the temperature of supercritical CO2, the residual water and initial cesium concentrations, and the amounts of extractant and modifier used. The yields from direct extraction were low (

The silica templating of Cu-HexaCyanoFerrate (HCF) is a classical technique which is often used to control the size and monodispersity thereby increasing the exposed surface area, and therefore the Cs sorption efficiency of what are normally highly aggregated nanoparticle systems. However, here we show that long term magnetic agitation of unfunctionalised aggregated Cu-HCF nanoparticles leads to a uniform and stable colloidal dispersion. This, we believe, is due to the intrinsic magnetic nature of Cu-HCF as seen by low temperature SQUID measurements. In this work we see that the Cs kinetics of magnetically dispersed Cu-HCF show a remarkable increase in the rate Cs sorption due particle disaggregation. Finally, the Cs sorption kinetics of these magnetically disaggregated particles proved similar to a chemically similar monodisperse silica templated sample.

Multiscale porous silica monoliths functionalized with potassium/copper hexacyanoferrate (HCF) have been evaluated for the column extraction of cesium from natural water. Compared with commercial silica gel particles, results show that the hierarchically porous architecture of the monoliths improves the bed efficiency in column extraction, and the selectivity, distribution coefficient and exchange kinetics in batch extraction. Cesium breakthrough experiments show that these preferable properties of the monolithic structure are maintained in column operation. This analysis of the batch and breakthrough experiments is supported by scanning and transmission electron microscopy data, residence time distributions, and reactive transport modeling assuming dispersive flow in the macroporous intraskeletal channels and diffusion inside the walls of the structure and the HCF aggregates.

This perspective focuses on the synthesis, characterization, and modeling of three classes of hierarchical materials with potential for sequestering radionuclides: nanoparticles, porous frameworks, and crystalline salt inclusion phases. The scientific impact of hierarchical structures and the development of the underlying crystal chemistry is discussed as laying the groundwork for the design, local structure control, and synthesis of new forms of matter with tailored properties. This requires development of the necessary scientific understanding of such complex structures through integrated synthesis, characterization, and modeling studies that can allow their purposeful creation and properties. The ultimate practical aim is to provide the means to create novel structure types that can simultaneously sequester multiple radionuclides. The result will lead to the creation of safe and efficient, long lasting waste forms for fission products and transuranic elements that are the products of nuclear materials ...

Radioactive wastewater contaminated with 137Cs and 90Sr are produced at different stages of the nuclear fuel cycle. Transferring these radionuclides to a stable solid matrix is crucial for safe wastewater management and long-term storage. Sitinakite Crystalline silicotitanates (CSTs) are among the most selective mineral ion exchangers for Cs and/or Sr depending on the pH of the medium and the CST chemical composition (Nb doping). To better understand how their microstructure affects their sorption properties, CSTs with different morphologies (consisting of submicronic to micronic particles) and Nb contents (from 0% to 25%) were synthesized and characterized in terms of their Sr2+ and Cs+ sorption properties at moderately basic pH. The Sr2+/Na+ and Cs+/Na+ equilibrium exchange diagrams obtained highlight the presence of two kind of sorption sites with different selectivities and sorption capacities. The first, kind of site, highly selective for Sr and less selective for Cs at moderately basic pH, was attributed to “tunnel” sites in the CST structure. The second one, less selective for Sr and Cs, seems to be a surface site. Although Nb doping was found to promote Cs sorption and hinder Sr sorption at moderately alkaline pH, the accessibility and selectivity of these two sites was found to depend more strongly on the microstructure of the CSTs. Results indicate that the more highly crystalline, micronic particles, with fewer structural defects, are more selective for Sr, but that the larger specific surface areas (greater number of surface sites) afforded by the submicronic particles are associated with larger sorption capacities.

Chemical, biological, radiological and nuclear (CBRN) accidents or attacks typically disseminate contaminants inside and outside buildings and structures whose surfaces have to be decontaminated. This paper describes an innovative colloidal gel formulation and its effects against CBR threat agents and also against prion contaminations. The gel’s rheological properties ensure it remains attached even to vertical surfaces. The gel then dries with the contaminants trapped inside, leaving behind non-dusting solid residues that are easy to recover by brushing or vacuum cleaning. The results obtained here on different formulations show that decontamination proceeds in two steps. Contaminants are first solubilized or absorbed into the gel thanks to the efficient wetting of the surface by the gel. Chemical and biological agents are then neutralized by the NaOH and hypochlorite ions in the gel. This article demonstrates the efficiency of this CBR gel against Bacillus anthracis, the chemical agents sulfur mustard, VX, and soman, 137Cs, and prion proteins.

The shaping of powdery zeolites into hierarchical materials is an objective for numerous applications. Emulsions can be used as a soft template to create porous and monolithic materials, but a fine understanding and control of the microstructure of the emulsions is crucial. By relating rheological, microscopic observations and microstructural properties, this study highlights the influence of the zeolite content (1–8 wt%) on the microstructure of high internal phase emulsions (HIPEs) stabilized by tetradecyltrimethylammonium bromide (TTAB)-covered zeolite particles. Pickering oil-in-water (O/W) emulsions are obtained at low surfactant/zeolite weight ratios (

The demand for effective and inexpensive treatment for decontamination of waters from radionuclides, such as 137 Cs, is presently high. In this context a selective adsorbent material for Cs (SORBMATECH 1 202) was designed, consisting of potassium/copper ferrocyanide nanoparticles deposited in the mesoporosity of silica grains. Several batch experiments were carried out in order to obtain kinetic and thermodynamic data concerning the ion exchange. Isotherms and measurements of distribution coefficients (K d,Cs ) in waters of increasing salinity (pure water, Ca-bicarbonate fresh water and seawater) were conducted in a radioactive environment. This study shows a fast ion-exchange kinetics (

Porous silica particles functionalized by potassium copper hexacyanoferrate (KCu-HCF@silica) are investigated as selective sorbents to remove radioactive cesium from contaminated effluents. This article reports the thermal behavior of Cs:KCu-HCF@silica particles at the laboratory scale, in view of developing hot isostatic pressing processes to compact the Cs-loaded particles into dense waste forms. The data show that the spent particles cannot be hot-pressed directly because the release of volatile compounds does prevent compaction. Preliminary calcination in air leads to (i) the decomposition of Cs:KCu-HCF, (ii) the closure of the mesopores of silica and a reduction in the particles’ specific surface area, (iii) the crystallization of silica into cristobalite, all without significant Cs loss. This retention of Cs is due to the in-situ formation of a Cs based silicate glass with the siliceous particles.

International audience; Industrial-scale rare earth extraction is typically performed by liquid-liquid extraction with large amounts of solvents, acids and organophosphorus ligands. An alternative is to use these extractants in supercritical CO$_2$ (SC-CO$_2$), where the crucial operating parameter is their solubility. Different molecules with amidophosphonate backbones have been synthesized and investigated in view of improving their solubility in SC-CO$_2$ and thereby their cerium extraction capacity. The CO$_2$-philicity of these extractants was adjusted by attaching branched or linear alkyl chains with four, six and eight carbons. Using a dynamic gravimetric setup, the solubility and cerium extraction capacity of these molecules were measured to vary from 1.56 to 2.47 mmol$_{ligand}$.mol$_{CO2}$$^{-1}$ and 0.25 to 0.46 mmol$_{Ce}$.mol$_{ligand}$$^{-1}$, respectively.The two properties were correlated and in both cases the highest values were obtained with a diisobutylamine chain. Solubility measurements between 313 and 331 K and between 13 and 28 MPa shows that optimal condition is (320 K ; 28 MPa).

International audience; As a step toward synthesizing zeolite-based porous materials, this study demonstrates for the first time the feasibility of stabilizing oil-in-water (O/W) high internal phase emulsions (HIPEs) using a cationic surfactant (tetradecyltrimethylammonium bromide, TTAB) and “homemade” submicronic Linde Type A zeolite particles. The zeolite particles are hydrophilic and therefore do not attach to dodecane-water interfaces but surface tension measurements and electrochemical data show that their surface can be activated by the electrostatic and subsequent hydrophobic adsorption of TTAB. Comparing the adsorption isotherm of TTAB and zeta potential of the particles with the droplet sizes and rheological properties of the emulsion shows that the stabilization mechanism depends on the TTAB/zeolite weight ratio. At low TTAB/zeolite weight ratios (≤ 0.2 wt %), gel-like O/W Pickering HIPEs form but at intermediate TTAB concentrations, the zeolite particles become more hydrophobic leading to phase inversion and the stabilization of W/O emulsions. At high TTAB/zeolite weight ratios (> 1.25 wt %), a second phase inversion occurs and creamy O/W HIPEs form through a different stabilization mechanism. In this case indeed, the zeolite particles are fully covered by a bilayer of TTAB and remain dispersed in the aqueous phase with no adsorption to the dodecane-water interface. The emulsion is stabilized by electrostatic repulsion between the highly positively charged zeolite particles and the cationic surfactant adsorbed at the dodecane-water interface.

International audience; Ion exchange resins (IERs) are used to treat radioactive liquid effluents from nuclear industry. Today, the management of spent IERs as nuclear waste is an issue. We propose here the use of hydrothermal and leaching treatments to transfer radioactivity from organic solid phase to aqueous phase, in order to connect to existing outlet systems. Co, Cs, Sr and Eu were chosen as α and βγ radionuclide surrogates. The efficiency of the treatment was assessed in terms of extraction yields and contaminant concentrations in wastewaters. The highest extraction efficiencies of 90–100 % were obtained in supercritical water in batch and semi-dynamic mode in the presence of oxidant. In subcritical conditions, yields adequate are lower but suitable with the disposal criteria for the residual solid waste. Complete extraction was also achieved by leaching with ethylenediaminetetraacetic acid solutions. The optimal choice between all these processes is therefore discussed with regards to the requirements of effluent treatment plant including post-treatment steps such as coprecipitation and advanced oxidation.

The removal of cesium contamination is a critical issue for the recycling of concrete rubble in most decommissioning operations. The high solvent strength and diffusivity of supercritical CO

Various functionalised silica materials have been investigated as uranium extractants from sulfuric acid solutions. Silica was grafted with zero, one or two amido and phosphonate groups either directly or by peptide coupling. The role of the residual functions (silanol, amine and amide) was evaluated. Our results show that the uranium extraction efficiency of materials bearing residual silanol or amide groups may be affected by the presence of molybdenum. Comparing the performance of materials with different numbers of phosphonic acids on the phosphonate group revealed that only those with a monoacid function extract uranium efficiently. Among these materials, those with a diamido phosphonate ligand demonstrated the highest selectivity for uranium versus iron. Adjusting the length and steric hindrance of the alkyl chains of the amido and the phosphonate group, the best extraction capacity and selectivity versus iron were achieved with a butyl group on the phosphonate and an ethyl group on the ternary amide of the diamido phosphonate ligand. Finally, the [ligand]/[U] ratio was found not to vary with the alkyl chain at the end of the amido group or with the bridge length between the carbamoyl monophosphonate extracting group and the amidopropyl anchor to the silica, suggesting that the extraction mechanism remains unchanged.

International audience

International audience; We study the extraction of strontium by sodium nonatitanate powder from nitrate strontium and acetate sodium mixture. Experiments show that adsorption is quantitative. The excess Gibbs free energy has been modeled by various models (ideal, 2D Coulomb, regular solution model) for the solid phase. We find that the free energy of the solid phase is controlled by short-range interactions rather than long-ranged Coulombic forces. The selectivity is the consequence of a competition between the liquid and solid phases: both phases prefer strontium rather than sodium but the solid contribution is predominant.

International audience; The feasibility of extracting uranium from natural ores has been studied, using supercritical CO2 and either commercial extractants (PC88A, Cyanex 301®) or an amidophosphonate molecule (named DEHCNPB). The impact of the process parameters has been evaluated. The uranium extraction yield was optimal at the lowest temperature (40 °C) and highest pressure (25 MPa) tested here. For a given CO2 flow rate, a compromise should be established between the amounts of extractant, acid and oxidant used. Uranium was successfully extracted directly from natural ore using DEHCNPB with a good selectivity over metal impurities such as iron, titanium and vanadium and yields up to 97%. Moreover, using Fe2(SO4)3 as an oxidant allows to minimize the water usage of the process. The mechanism of extraction using supercritical CO2 has been elucidated thanks to electrospray ionization mass spectrometry.

International audience; Sodium nonatitanate powder is a layered material containing some potential exchangeable sodium ions between layers. In this work, sorption mechanism of this material has been studied and modeled at the solid-liquid interface. In particular, the ion-exchange mechanism is up to now not entirely known and especially the role of the pH on sorption properties. To investigate this latter, the solid is first equilibrated with inert acidic and base (nitric acid and triethylamine) for which the co-ions nitrate and triethylammonium do not penetrate the solid. The exchange between proton or divalent ions (strontium or calcium), and the sodium initially located in the sodium nonatitanate, is characterized through capillary ionic chromatography and conductivity experiments. To understand and explain the sorption properties, we modeled the equilibrium constant of different exchange reactions as a function of the solution pH. The equilibrium constants of the strontium/sodium and the calcium/sodium exchange have been obtained. We have shown the important role of the pH on the sorption rate of the strontium and moreover the hydrolysis rate of the sodium nonatitanate is calculated. We found that one eighth of sodium is spontaneously hydrolysed in aqueous phase whereas seven-eighths are exchanged by different divalent cations (strontium or calcium). Strontium and calcium exhibit similar exchange curves and competition with the proton adsorbed is modeled with global equilibrium constant. The prediction is in agreement with the conductivity experiments and the global extraction isotherms.

International audience; This 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.

A series of five silica supports with different pore diameters were functionalized in two steps by post-grafting, producing three types of material: (1) initial supports with pores smaller than 4 nm are heterogeneously functionalized because of steric effects; (2) when the pores range from 5 to 20 nm in diameter, a homogeneous organic monolayer is grafted onto the silica skeleton; and (3) when the pores are larger than 30 nm, an organic multilayer covalently linked to the surface is obtained. These hybrid materials were then used to extract uranium from a sulphuric solution. Our results show that the efficiency, capacity and selectivity of the extraction can be controlled through the effect the initial pore size has on the organic structures that form therein. After regeneration moreover, these materials can be reused with the same efficiency.

International audience; Growing interest in radioactive effluent treatment, especially after the Fukushima nuclear accident, has led to the development of new, increasingly efficient mineral sorbents. The sorbents currently attracting the most attention are materials dedicated to strontium extraction. The Ba-titanate material investigated here, combining several sorption mechanisms, has a high capacity and selectivity for strontium with a distribution coefficient, K$_d$, of 863 mL g$^{−1}$, obtained from a batch sorption test with seawater ([Sr] = 9 × 10$^{−5}$ mol L$^{−1}$; titanate concentration, 1 g L$^{−1}$). This K$_d$ is six times higher than that of Na-titanate, one of the strontium sorbents used for multi-nuclide removal at the Fukushima-Daiichi nuclear power station. Upon contact with the sulfate-containing effluent, Sr extraction proceeds by ion exchange with the Ba ions inserted in the material and by coprecipitation with insoluble barium sulfate formed at the surface of the titanate grains.