Appearance of dark neurons following anodal polarization in the rat brain.

An anodal direct current of 3.0 microA or 30.0 microA was unilaterally applied for 30 min or 3 h to the surface of the sensorimotor cortex of rats, and the effects of polarization on the morphology of brain cells were examined by light microscopy. After five repeated anodal polarization trials, dark neurons appeared mainly in the polarized neocortex regardless of the intensity and duration of the polarizing currents. Such dark neurons were scarce in the control animals or the animals receiving only one trial of polarization. The dark neurons were most abundant in the second to fourth layers of the ipsilateral superior-lateral convexity of the frontal cortex, but a few were present in the contralateral cortex. The dark neurons began to appear 24 h after the last polarization; thereafter almost all of these neurons gradually reverted to their normal morphological profiles through a transitory state within 1 month of the last trial of repeated polarization. No morphological changes were apparent in any of the brain structures other than the cerebral cortex. These findings indicate that repeated anodal polarization has reversible morphological effects on the cortical neurons, suggesting that the appearance of dark neurons after anodal polarization is an important index for evaluation of cortical plastic change induced by polarization.</p

The REPUTER project for Ni-MH battery recycling

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Élaboration de matériaux hybrides fonctionnalisés de type MOF pour l'extraction sélective de l'uranium

International audienc

Rare earth recovery and separation using diglycolamides

International audienceRare earth elements (REE) have become essential for our modern economy, in relation to the development of new energy and communication technologies. Depending on their technical-economic efficiency and environmental footprint, hydrometallurgical processes enabling the recovery of separated elements could be of particular interest.Typically these processes include a first pre-treatment (crushing, milling and sieving) and an acidic leaching step (with eventual selective precipitation sub-steps), followed by a solvent extraction (SX) step aimed at the separation and purification of REE. Recently, diglycolamides (DGA) appeared as a very interesting group of extractants for the selective recovery of trivalent REE from nitric acid solutions, particularly in the presence of transition metal ions commonly found in various waste products. In this work, the TODGA extractant was successfully used for designing an efficient REE recovery process. The process integrates the mechanical and physico-chemical treatment of waste, followed by a solvent extraction step for the recovery and intra-separation of REE. Based on the experimental batch data, a phenomenological model has been elaborated taking into account the various distribution equilibria. The model has been implemented in our simulation code and used for calculation of various flowsheets, which have been tested at our pilot facility using compact continuous counter-current mixer-settlers. Experimental SX and modeling data allowing the recovery of >99.95% pure Dysprosium solution will be discussed in this paper. Preliminary technical-economic assessment and life-cycle analysis have also been conducted. Following this first successful demonstration, several novel dissymmetrical DGA have been developed and their solvent extraction behaviour in different acid media has been studied. Indeed, most processes use symmetrical DGA such as TODGA. The present work improves upon the classic design and demonstrates that novel dissymmetrical extractants display a remarkable improvement on REE extraction efficiency compared to reference TODGA in various acid media. Furthermore, the REE separation factors towards major impurities such as Fe3+ are substantially enhanced.The development of novel DGA with increased efficiency paves the way for the recovery and separation of high value REE from different streams. This opens new market opportunities since the effluent treatment has often an important impact either in the CAPEX or the OPEX of a solvent extraction plant. With some DGA extractants adapted to sulfuric acid media, the resulting effluent treatment plant could be cheaper than it would be using nitric acid media. Furthermore, their enhanced performance at low concentration should reduce the price of reagents in the OPEX

Development of MOF-type Hybrid Functionalized Materials for Selective Uranium Extraction

International audienceDifferent types of materials have been developed for the solid/liquid uranium extraction processes, such as functionalized organic polymers, hybrid silica or inorganic adsorbents. In general, these materials exhibit a moderate affinity for uranyl ions and poor selectivity against impurities like iron, vanadium or molybdenum. Moreover, the structural organization deficiency of these materials generates ion diffusion issues inside the material. Therefore, the aim of our study is to developed novel efficient and organized materials, stable in the acid media encountered in uranium extraction processes.Metal organic frameworks (MOFs) are hybrid crystalline materials consisting of an inorganic part (cluster or metal ions) and tailored organic linkers connected via coordination bonds. These hierarchical materials have exceptional surface area, thermal stability and a large variety of tunable structures. However, due to the reversibility of constitutive coordination bonds, MOFs have moderate stability in strongly complexing or acidic media. Only few of them are known to be stable in aqueous media and only one example is described in strong acidic media. However, these conditions are very often encountered in the environmental pollution remediation of mine wastewaters. To tackle the challenge of developing MOFs adapted for uranium extraction from acid mine waters, we have investigated the stability of several materials. To ensure a good stability we have synthetized and characterized different materials based on highly coordinated metal clusters, such as LnOFs and Zirconium based materials. Among the latter, the UiO family shows a great stability in sulfuric acid media even in the presence of 1.4 M sodium sulfate at pH 2. However, the stability in phosphoric media is reduced due to the high affinity between zirconium and phosphate ligand. Based on these results, we have developed a tertiary amine functionalized MOF denoted UiO-68-NMe2 particularly adapted for the extraction of anionic uranyl(VI) sulfate complexes mainly present in the acid mine solutions. The adsorption capacity of the material has been determined upon varying total sulfate concentration, contact time and uranium concentration. The extraction tests put in evidence different phenomena due to the complexity of the extraction media and the interaction between the MOF and sulfate anion. Finally, the extraction mechanisms and the interaction between uranyl and the MOF structure have been investigated. The functionalized material UiO-68-NMe2 has been characterized in the presence and absence of uranium by FT-IR, UV and Raman techniques. Moreover, the stability of the protonated amino functionalized MOF has been evaluated. The synthesis, characterization and evaluation of this type of hybrid material, particularly adapted for uranium extraction in sulfuric acid media by an anionic exchange mechanism, paved the way for the development of novel metal organic frameworks functionalized by different other chelating motifs, such as bifunctional ligands showing an enhanced affinity and selectivity for uranium in acid and complexing media. Work in this direction is currently in progress

Optimization of novel bifunctional ligand design for uranium extraction

International audienceUranium is recovered from natural primary and secondary resources by hydrometallurgical processes including ore leaching and purification. Different processes are available for uranium extraction and separation from the associated elements, but the most widely used remains the liquid-liquid extraction. Improving the performance of current processes through the design of more efficient, selective and robust extractants is particularly important. To optimize the liquid-liquid extraction of uranyl (UO$_2$$^{2+}$) from highly complexing sulfuric or phosphoric acid solutions, an approach based on the design of bifunctional extractants combining in the same molecular architecture both cation exchanger and neutral-donor functionalities has led to the development of a new family of ligand molecules containing a pyridine $N$-oxide ring and an acidic phosphonate function. Several novel molecules have been synthesized using an optimized strategy. The affinity and selectivity of the extractants were evaluated by batch liquid-liquid extraction tests and very high distribution ratios of uranium(VI) were measured (D$_U$ > 4200) in the presence of large concentrations of complexing anions such as sulfates. However, the separation factor of U(VI) versus Fe(III) is low.To establish structure-activity correlations and understand the lack of selectivity of this family towards Fe(III), the molecular environment around U(VI) and Fe(III) cations has been investigated using a combination of experimental (UV-vis and FT-IR spectroscopy, ESI-MS spectrometry) and theoretical approaches. Density functional theory (DFT) calculations coupled to infrared spectroscopy have been performed in order to identify the chemical functions contributing to the uranyl (UO$_2$$^{2+}$) coordination environment. The acidity (p$K_a$) and the complexation constants (log$\beta$) of these new ligands were measured using UV spectroscopy. The influence of the molecular design on the efficiency of the molecules to selectively extract U(VI) versus Fe(III) from sulfuric and phosphoric acid solutions was thus established. The present studies will contribute to a better understanding of the factors influencing the extraction properties and will lead on the longer term to the development of improved uranium extraction processes by organic ligands

Design of optimised chelating agents for cesium extraction in supercritical CO2_2

International audienc

Development of a new process for the selective rare earth recovery from used permanent magnets

International audienceAlbeit being considered today as the most critical raw materials group with the highest supply risk, the recycling of rare earth elements (REE) from permanent NdFeB magnets is almost inexistent. Therefore, a large research effort is needed for over-coming the current scientific and technological barriers and improving the recycling efficiency. Innovative, profitable and eco-designed processes have to be developed, which require extensive R&D effort from basic research to technological developments. The CEA has gained a world-class expertise in the field of separation processes by hydrometallurgy and pyrometallurgy, several solvent extraction processes being developed and industrially implemented for the nuclear fuel cycle. In this communication, an efficient combined hydro- and pyrometallurgical process aimed at REE recovery and separation from used or refurbished NdFeB permanent magnets will be presented. The process integrates the mechanical and physico-chemical treatment of NdFeB magnets, followed by a solvent extraction step for the recovery and intra-separation of REE using a selective extracting molecule with excellent affinity for heavy REE (Dysprosium) which are today the most critical REE. A solvent extraction flow sheet was calculated and tested in laboratory-scale mixer-settlers from a genuine solution of permanent magnets leached in nitric acid. More than 99.9% of dysprosium and neodymium were recovered in two different streams with purities higher than 99.99%. A subsequent pyrometallurgical treatment via molten chloride salt electrolysis allowed the isolation of pure Dy metal with excellent faradic yields. Based on these results, a first techno-economic analysis was made to scale-up the process at an industrial scale and will be presented in the paper. This is one of the first examples of an effective, closed-loop REE recovery and separation process, starting from magnet scrap down to individual pure REE as metals, which paves the way for future developments in the field

A combined hydro- and pyrometallurgical process for REE recovery from used permanent magnets

International audienceRare earth elements (REE) have become essential for our modern economy, in relation to the development of new energy and communication technologies. Albeit being considered today as the most critical raw materials group with the highest supply risk, the recycling of REE from electronic waste and end-of-life products (permanent NdFeB magnets, Ni-MH batteries etc.) is almost inexistent. Therefore, a large research effort is needed for overcoming the current scientific and technological issues and improving the recycling efficiency. Innovative, eco-designed processes have to be developed, which require extensive RandD effort from basic research to technological developments

Future challenges in hydrometallurgy for critical metal recovery and recycling RadioChemistry and Processes Department CEA Marcoule

International audienceThe demand for certain critical metals including rare-earths has recently increased, in relation to the development of new energy and communication technologies. Various initiatives such as recycling and prospection of new resources have been launched to reduce the European dependence on foreign suppliers. Hydrometallurgy is essential for the valorization of these poly-metallic resources in which the critical elements are often in low concentrations among numerous impurities. Innovative and environmental-friendly processes have to be developed to recover these elements, which require extensive RetD from basic research to technological developments.The CEA has gained a world-class expertise in the field of separation processes by hydrometallurgy. Several solvent extraction processes have been developed and industrially implemented for the nuclear fuel cycle. More recently, CEA developed processes to support the recycling of critical materials for energy technologies (Li-ion batteries, fuel-cells). In this framework, the RECAPE project aims to develop an efficient recovery process of heavy rare-earth elements by hydrometallurgy from used permanent magnets. Experimental and modeling results will be presented in this paper. More generally, CEA aims to enhance the coordination and integration of the European community in the field of RetD on critical materials recovery and recycling. This strategy will include both the creation of a European Institute of Hydrometallurgy to allow the industrial qualification of separation processes and the launching of a European research network to support innovation in the field of critical metals