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A vertical-flow unit containing four filters filled with shale was used to study the removal of phosphorous, nitrogen and organic matter of an urban residual wastewater during a period of 90 days. The influence of both the shale granulometry and the plant density of Panicum Maximum were studied. The decrease of the shale granulometry led to a significant improvement of all the measured parameters, while the presence of plants did only influence the phosphate retention with a lower extent. By comparing the results to previous studies, we hypothesised that the effect of the root system of Panicum maximum would be different depending on the size and the depth of the reactors. For practical application, adjusting the material granulometry was proposed to be the most important parameter for improving the filtration efficiency. Concomitantly, adjusting the plant density helps to control the clogging percentage of the filters.

International audience; This article reports for the first time the synthesis of an LDH using only manganese as the divalent and trivalent metallic ion. Analysis of the pH, redox potential, and chemical composition during the oxidation of a manganese basic salt using persulfate indicates the oxidation of 1/3 of the initial MnII ions, in agreement with the paramagnetic structure and XPS analysis. Infrared, Raman spectra and thermogravimetric analysis results were similar to the ones obtained with Fe-LDH also known as green rust. X-Ray diffractograms and Rietveld refinement were used to determine the structure of this solid. Thermodynamic considerations predict that this solid could reduce nitrate into gaseous nitrogen without further reduction to ammonium or ammonia unlike what is observed for Fe-LDH.

Understanding the mechanisms of the interactions between zinc-based layered double hydroxides (LDHs) and bacterial surfaces is of great importance to improve the efficiency of these antibiotic-free antibacterial agents. In fact, the role of surface interactions in the antibacterial activity of zinc-based LDH nanoparticles compared to that of dissolution and generation of reactive oxygen species (ROS) is still not well documented. In this study, we show that ZnAl LDH nanoparticles exhibit a strong antibacterial effect against

Infections by pathogenic bacteria have been threatening several fields as food industries, agriculture, textile industries and healthcare products. Layered double hydroxides materials (LDHs), also called anionic clays, could be utilized as efficient antibacterial materials due to their several interesting properties as ease of synthesis, tunable chemical composition, biocompatibility and anion exchange capacity. Pristine LDHs as well as LDH-composites including antibacterial molecules and nanoparticles loaded-LDHs were proven to serve as efficient antibacterial agents against various Gram-positive and Gram-negative bacterial strains. The achieved antibacterial effect was explained by the following mechanisms: (1) Direct contact between the materials and bacterial cells driven by electrostatic interactions between positively charged layers and negatively charged cell membranes, (2) Dissolution and gradual release over time of metallic ions or antibacterial molecules, (3) Generation of reactive oxygen species.

International audience

Synthesized palladium-coated iron-iron oxide (Fe@FeOx/Pd) nanoparticles (NPs) using the successive salt reduction method are tested for their activity and stability toward formate oxidation (FO) and electrochemical CO2 reduction to formate (eCO2RF). The experimental results for FO show a current density at 0.12 V vs. Ag/AgCl of 1.65 mA/cm2 over 1 h, which is 16 times higher than that for Pd NPs. Furthermore, the same catalyst displays a higher current density with a faradaic efficiency (FE) of 95.6 % toward the eCO2RF, and exhibits a lower degree of CO adsorption. The iron-iron oxide interaction with the overlayer palladium is characterized by TEM/EDX, XPS/UPS, Mossbauer spectroscopy, and electrochemical techniques such as cyclic voltammetry (CV) and chronoamperometry (CA). NMR is used to estimate the amount of formate produced by the eCO2RF. A positive binding energy shift of the Pd 3d peak and the upshift of the d-band center as measured by XPS compared to monometallic homemade Pd NPs confirm that the electronic perturbation of the catalyst surface plays a major role in enhancing the performance of Fe@FeOx/Pd for both FO and eCO2RF. Furthermore, the work function as measured by UPS for the Fe@FeOx/Pd material is lower than that for monometallic Pd confirming a change in chemical properties of the catalyst surface. Finally, Mossbauer spectroscopy is used to determine the composition, structure and nature of all sites of the Fe@FeOx substrate before use and the perturbation of their intrinsic properties by the Pd overlayer. This change in intrinsic properties of the Pd coated material provides additional explanations for the electrochemical improvement measured for this catalyst toward both FO and eCO2RF

Layered double hydroxides (LDHs) have been intensively studied for phosphate (Pi) removal but suffer from poor stability and low sorption affinity under ambient conditions. In this paper, well crystallized MnIIFeIIFeIII-Cl, MnIIFeIII-CO3 and novel MnIVFeIII-CO3 LDHs were synthesized. The LDHs show fast Pi sorption with 90 % uptake within 20 min, and high Pi sorption capacity of 11 mg P/g at low solution Pi concenrations of 0.1 mg P/L, corresponding to a very high Pi sorption affinity (Kd 1.1 × 105 L/kg). Fast MnII dissolution from the MnIIFeIIFeIII-Cl LDHs and formation of MnFe2O4 at pH 7 were observed in aqueous suspensions of non-oxidized material where up to 70% of total Mn was released within 2 h. However, when interlayer Cl- was exchanged with CO32−, much lower Mn dissolution (5.4%) was observed. Furthermore, after oxidation of MnII to MnIV, the obtained MnIVFeIII-CO3 LDH maintained the layered structure of LDH and the particles were surrounded by birnessite nanorods. The MnIVFeIII-CO3 LDH showed excellent stability but lower Pi sorption capacity. However, a high sorption affinity was maintained which is attributed to more positively charged Fe-centered sorption sites. XPS and ATR-FTIR data together with DFT calculations demonstrated that Pi was mainly sorbed via the formation of mononuclear mono- and bidentate Pi surface complexes on planar LDH particle surfaces.

International audience; It is expected that during a titration using a basic NaOH solution, the pH can only increase. In this article the formation of two different solids during the precipitation of a MnSO 4 solution is discussed. The formation of a new compound Mn 4 (OH) 6 SO 4 • nH 2 O instead of Mn(OH) 2 is evidenced by the quantification of the remaining ions in solution as well as by X-Ray Diffraction, Raman and infrared spectroscopies. The transformation of this solid into Mn(OH) 2 after a sursaturation of the solid in OHcan explain a drop of the pH in the titration curve.

A vertical-flow unit containing four filters filled with shale was used to study the removal of phosphorous, nitrogen and organic matter of an urban residual wastewater during a period of 90 days. The influence of both the shale granulometry and the plant density of

Iron and cobalt monometallic Layered Double Hydroxide (LDH), combining divalent and trivalent cations of the same chemical element, are commonly used respectively for nitrate reduction and oxygen evolution reaction. This article reports the first synthesis of a LDH using only manganese as metallic ion. X-Ray diffractograms, infrared and Raman spectra show that the structure obtained through the oxidation of a basic Mn II salt with persulfate is comparable to the structure of Fe-LDH also known as Green Rust. XPS shows that in this solid coexist Mn II and Mn III states. Thermodynamic considerations predict that this solid can reduce nitrate into gaseous nitrogen without further reduction into ammonium or ammonia unlike what is observed for Fe-LDH. Keywords Mn 6 (OH) 12 SO 4 • LDH • Mn • Green rust • Mn basic salts • XPS • XRD • Raman • IR • SEM • Monometallic LDH • Water remediation • Nitrate reduction • Pourbaix diagram • Thermodynamic calculation

Iron and manganese are ubiquitous in the natural environment. FeII-FeIII layered double hydroxide, commonly called green rust (GR), and MnIII-MnIV birnessite (Bir) are also well known to be reactive solid compounds. Therefore, studying the chemical interactions between Fe and Mn species could contribute to understanding the interactions between their respective biogeochemical cycles. Moreover, ferromanganese solid compounds are potentially interesting materials for water treatment. Here, a {Fe(OH)2, FeIIaq} mixture was oxidized by Bir in sulphated aqueous media in the presence or absence of dissolved O2. In oxic conditions for an initial FeII/OH&minus, ratio of 0.6, a single GR phase was obtained in a first step, the oxidation kinetics being faster than without Bir. In a second step, GR was oxidised into various final products, mainly in a spinel structure. A partial substitution of Fe by Mn species was suspected in both GR and the spinel. In anoxic condition, GR was also observed but other by-products were concomitantly formed. All the oxidation products were characterized by XRD, XPS, and M&ouml, ssbauer spectroscopy. Hence, oxidation of FeII species by Bir can be considered as a new chemical pathway for producing ferromanganese spinels. Furthermore, these results suggest that Bir may participate in the formation of GR minerals.

Developing low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min–1 and an initial phosphate concentration of 25 mg L–1 showed a breakthrough point at a V/Vp value of ~17, where V is the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.

Qu’est-ce qui fait un refugie ? Est-ce meme le juste terme ? Pourquoi pas migrant, sans papier, apatride, demandeur d’asile… ? Telles sont les questions a l’origine de cet ouvrage. Qui choisit tel terme pour designer telle personne, et ce terme dit-il vraiment quelque chose sur l’individu qu’il est cense designer ? Questions qui ne sont pas simples a resoudre, lorsqu’il s’agit des etrangers et des crises de leur reception sur le territoire (ici francais, mais cela pourrait etre etendu). Non s...

Layered double hydroxides (LDH) and their magnetic composites have been intensively investigated as recyclable high-capacity phosphate sorbents but with little attention to their stability as function of pH and phosphate concentration. The stability of a Fe3O4@SiO2-Mg3Fe LDH P sorbent as function of pH (5–11) and orthophosphate (Pi) concentration (1–300 mg P/L) was investigated. The composite has high adsorption capacity (approx. 80 mg P/g) at pH 5 but with fast dissolution of the LDH component resulting in formation of ferrihydrite as evidenced by Mössbauer spectroscopy. At pH 7 more than 60% of the LDH dissolves within 60 min, while at alkaline pH, the LDH is more stable but with less than 40% adsorption capacity as compared to pH 5. The high Pi sorption at acid to neutral pH is attributed to Pi bonding to the residual ferrihydrite. Under alkaline conditions Pi is sorbed to LDH at low Pi concentration while magnesium phosphates form at higher Pi concentration evidenced by solid-state 31P MAS NMR, powder X-ray diffraction and chemical analyses. Sorption as function of pH and Pi concentration has been fitted by a Rational 2D function allowing for estimation of Pi sorption and precipitation. In conclusion, the instability of the LDH component limits its application in wastewater treatment from acid to alkaline pH. Future use of magnetic LDH composites requires substantial stabilisation of the LDH component.

International audience; Single phase Casingle bondFe layered double hydroxide (LDH) minerals containing Cl− species in the interlayer was synthesized by coprecipitation with a CaII: FeIII ratio of 2: 1. In both phosphate (PO4) free water and at low aqueous PO4 concentration, the LDH was fully transformed into a mixture of a “ferrihydrite-like” material, calcite and soluble calcium species. Mössbauer spectroscopy and transmission electron microscopy showed that phosphate was removed by the “ferrihydrite like” phase that contained a significant quantity of Ca. At high phosphate concentration the Ca species released from the LDH precipitated to form hydroxyapatite leading to a maximal removal capacity of ~ 130 mg P-PO4 g−1. The Casingle bondFe LDH was deposited onto a pozzolana volcanic rock in order to perform a column experiment under hydrodynamic conditions for 70 days. A high removal capacity was observed, a qB of ~ 4 mg P-PO4 g−1 was measured at the breakthrough of the column, however the pH in the outflow was measured to be higher than 11. Such an increase was due to the very high solubility of the Casingle bondFe LDH.

Birnessite is a ubiquitous natural Mn oxide. This layered material is involved in a large variety of ion-exchange and redox reaction in soils and sediments. Synthetic Na-triclinic birnessite with a general formula [MnIII0.35 MnIV0.65 O2][Na+0.35 0.7H2O] was converted into hexagonal birnessite by acidic treatment at pH = 3.5. Both solids were fully characterized by TEM, SEM, PXRD, FTIR, Raman scattering, 23Na as well as the first 1H MAS NMR birnessite spectra were reported. The surfaces of both forms were fully analyzed by XPS: a particular attention was paid to the determination of the oxidation state of Mn derived from the fitting of XPS Mn 3p or Mn 2p3/2 features. An excess of reduced Mn at the surface in comparison to the bulk materials was evidenced.

Il est necessaire de reprendre la question de l’emancipation a l’egard de la figure du spectateur d’art d’exposition. Autant parce que le theme de l’emancipation appartient au champ de l’esthetique des sa constitution que parce que l’« emancipation » s’y entend aussi dans les quatre sens advenus depuis les Lumieres : en sus des sens juridique et historien, le sens prete par les Lumieres (l’emancipation par la critique) est battu en breche par un autre sens acquis au sein des philosophies de l’histoire (l’emancipation critique), puis dans la signification pretee par l’ecole de Francfort et, enfin, dans l’emancipation-subjectivation a la Jacques Ranciere. L’interet du travail de ce dernier est de souligner que, lorsqu’on parle de l’emancipation-subjectivation, il ne s’agit ni de changer de place afin de mieux voir le spectateur, ni de le changer de place, de l’agiter ou de deplacer son corps ailleurs, ni d’echanger le point de vue du spectateur pour un autre point de vue.

A destination des etudiants, les instruments du travail intellectuel – textes reduits, expliques, commentes, surlignes… – foisonnent, le plus souvent entre reduction des theories au minimum vital pour survivre a un examen et reiteration de ce que tout le monde repand dans les manuels les plus divers. L’ideal pedagogique, pour ne pas dire la justification, en est toujours d’aider les etudiants a reussir leurs concours et autres epreuves ecrites et orales. Le manque d’originalite en cette matie...

International audience; Ultrathin iron oxide particles are of high interest due to their large surface areas and unusual physical and chemical properties. Previous works have shown that single sheet iron oxides (SSI) can be formed via delamination of oxidized layered iron (hydr)oxides (green rusts, GR) interlayered by dodecanoate. However, there is considerable uncertainty on the true structure of both starting material and final products, and the reaction pathway. In this work, we describe a robust method for SSI synthesis and provide detailed structural characterization of the initial, intermediate and final phases to decipher the reaction mechanism. The SSI product has the formula FeO0.82(OH)1.38·0.7H2O, and consists of platelets with a height of 1 nm and lateral dimensions of 20 to 100 nm as observed by Atomic Force Microscopy and Transmission Electron Microscopy. Mössbauer spectroscopy from 300 to 9 K shows that SSI is distinct from goethite, ferrihydrite and feroxyhite. Pair distribution function (PDF) analysis of high energy X-ray scattering data reveals that SSI has two distinct nearest neighbor FeFe distances in contrast to the single distance in the parent FeII-FeIII (hydr)oxide composed of entirely edge-sharing octahedra. Modeling of the SSI PDF data indicates that oxidation of FeII to FeIII of dodecanoate-intercalated green rust results in displacements of Fe atoms perpendicular from the parent iron (hydr)oxide layer, forming a material that consists of iron polyhedra linked by both corner- and edge-sharing. This model which is different from the previously published model, matches the measured SSI thickness and electron diffraction pattern. This elucidated reaction pathway confirms that the dodecanoate interlayers in GR hinders Fe polymerization across interlayers and thus restrict chemical transformations to largely two-dimensional space. The increase of single- and double- coordinated O/OH groups in the SSI compared with the parent GRs is expected to give a high reactivity of SSI as surface complexation sorbents.

International audience; Aqueous phosphate removal by three geomaterials from Ivory Coast was evaluated to determine their potential application as low-cost phosphate adsorbents in wastewater treatment. Batch experiments showed that phosphate uptake strongly depended on pH. Laterite and sandstone dissolution was less pronounced compared to shale. A correlation between concentrations of aqueous cation species released from shale and phosphate uptake was observed. The kinetics were well described using the pseudo-second-order model. Isotherms displayed a saturation level on shale, while phosphate uptake continuously increased for laterite and sandstone. The removal efficiency decreased in the following ranking order: laterite > sandstone > shale. Laterite was also the most efficient adsorbent in column experiments. The high phosphate removal efficiency of laterite (8.3 mg PO4 g−1) was attributed to the presence of superparamagnetic low grain sizes of goethite. Laterite is a particularly promising material for further investigation in wastewater treatment technology such as constructed wetlands.

International audience; In the anoxic conditions of nuclear waste deep geological repository, the main iron corrosion products formed at the surface of the carbon steel overpacks are siderite (FeIICO3) and magnetite (FeIIFeIII2O4) that form a rather protective layer. The originality of this work is the consideration of the bacterial metabolism of nitrate-reducing bacteria (NRB), often overlooked in corrosion processes. Klebsiella mobilis was used as a model of NRB and incubated with ferrous carbonates/magnetite corrosion bilayers under anoxic conditions. As a consequence of a combination of biotic and abiotic processes magnetite was reduced to mackinawite (FeIIS) and subsequently transformed to greigite (FeIIFeIII2S4).

Mossbauer spectroscopy characterizes “Green rust related minerals” of the fougerite group within the hydrotalcite supergroup (Mills et al. Mineral. Mag. 76(5), 1289–1336, 2012) in locations on Earth quite different from the original studies done in a temperate climate such as Brittany- France, Western Europe. Two examples are described, the gley at the bottom of Tatkul Lake in South Urals (Russia), which is representative of permafrost conditions, and a gley at the bottom of Yanga Lake, a reservoir in the Murray River catchment (NSW-Australia), which is representative of warm and desert conditions. Complementary information is obtained from XRD patterns.

International audience; Magnetite ((FeFe2O4)-Fe-II-O-III) is often considered as a stable end product of the bioreduction of Fe-III minerals (e.g., ferrihydrite, lepidocrocite, hematite) or of the biological oxidation of Fe-II compounds (e.g., siderite), with green rust (GR) as a mixed Fe-II-Fe-III hydroxide intermediate. Until now, the biotic transformation of magnetite to GR has not been evidenced. In this study, we investigated the capability of an iron-reducing bacterium, Shewanella putrefaciens, to reduce magnetite at circumneutral pH in the presence of dihydrogen as sole inorganic electron donor. During incubation, GR and/or siderite ((FeCO3)-C-II) formation occurred as secondary iron minerals, resulting from the precipitation of Fe-II species produced via the bacterial reduction of Fe-III species present in magnetite. Taking into account the exact nature of the secondary iron minerals and the electron donor source is necessary to understand the exergonic character of the biotic transformation of magnetite to GR, which had been considered to date as thermodynamically unfavorable at circumneutral pH. This finding reinforces the hypothesis that GR would be the cornerstone of the microbial transformations of iron-bearing minerals in the anoxic biogeochemical cycle of iron and opens up new possibilities for the interpretation of the evolution of Earth's history and for the understanding of biocorrosion processes in the field of applied science.

International audience; Ca-Fe layered double hydroxide (LDH) intercalated with chloride and nitrate ions has been synthesized with varying Ca-II:Fe-III molar ratios of the initial solution. Phase pure LDH is observed with Ca-II:Fe-III molar ratio of 2:1 and a mixture of LDH and Ca(OH)(2) is formed for Ca-II:Fe-III molar ratios higher than 2:1. Vibrational spectroscopies (Raman and IR) were used successfully to understand the interaction between the cationic and anionic sheets. The Raman bands positions at lower frequencies (150-600 cm(-1)) are intimately correlated to the nature of the divalent and trivalent ions but also to the nature of the anions. Indeed, a shift of similar to 9 cm(-1) is observed for the Raman double bands situated in the 300-400 cm(-1) region when comparing Raman spectra of CaFe-LDH containing either nitrate or chloride ions. Two types of nitrate environments are observed namely free (non-hydrogen bonded) nitrate and nitrate hydrogen bonded to the interlayer water or to the `brucite-like' hydroxyl surface. Multiple types of water structure are observed and would result from different hydrogen bond structures. Water bending modes are identified at 1645 cm(-1) greater than the one observed for LDH intercalated with chloride anions (1618 cm(-1)), indicating that the water is strongly hydrogen bonded to the nitrate anions.

The preparation optimization of a filter material intended to be used as a phosphate sorbent in flow-through conditions is investigated. The mixing of ferrihydrite (Fh) and pozzolana (Pz) using a “dry contact method” is found to be the most efficient and leads to the formation of a micrometric thick Fh coating deposited into the honeycombed structure of Pz. The maximal Fh content of ~8.5 wt.% is significantly higher than the quantity deposited on other classical substrates such as sand. The phosphate sorption kinetics and isotherms, under dynamic conditions in batch experiments, are best described by pseudo-second-order and Freundlich models respectively. Moreover, under static conditions, sorption kinetics reveals intra-aggregate diffusion process. Phosphate ion retention in packed columns, and especially the breakthrough point, can be adequately predicted when coupling the classical convection dispersion equation and the surface complexation model. Breakthrough curves of phosphate ions are strongly dependent on flow rate; which is important for future industrial applications. Finally, and unexpectedly, a high value of phosphate adsorption capacity (80 mg PO4 g−1) is observed when phosphate-containing wastewater is used as feed solution. This is mostly explained by soluble calcium ions, which favors the phosphate fixation onto the filter material surface. Keywords: Ferrihydrite, Pozzolana, Phosphate, Flow through, Adsorption

The ease of preparation as well as the fine tuning of their chemical composition makes layered double hydroxides (LDH) very attractive for a large variety of applications. The aim of this feature article is to provide the keys that permit to finely tune the structure of the materials in controlling simple parameters involved in the synthesis procedures. In a first part, the influence of the synthesis parameters on the crystallinity and morphology of MII-FeIII LDH (MII = NiII, MgII and CoII) is studied. In a second part, further insight into the variability of composition of the layer is proposed to explain the interdependence between the cationic nature of the layer and its layer charge flexibility. The third part is devoted to the anion exchange property of LDH. We showed that a previously proposed method for anionic exchange can be successfully applied to all couple of cations in their range of composition. Finally, a molecular description of the interlayer organisation is given.

Il y a bien du langage partout, pensait Honore de Balzac. Tout objet compose une partie du vaste poeme qui est le poeme de la societe s’ecrivant elle-meme, dans la multitude des signes. Honore de Balzac deploie alors un programme linguistique et geologique de degagement des couches et de lecture des objets comme hieroglyphes ou fossiles exprimant les epaisseurs des mœurs et de l’histoire. Ce n’est sans aucun doute plus de cette maniere que les sociologues prennent la question des objets, mais...

On peut prendre sur les institutions culturelles bien des points de vue. Mais ce n’est pas uniquement une affaire de choix de perspectives scientifiques (sociologie, histoire, psychologie...), parfois croisees ou non. C’est aussi le resultat necessaire des veritables mutations subies par ces institutions ces dernieres annees, a l’instar des changements sociaux plus globaux. Mutations qui concernent autant le rapport des institutions a elles-memes que celui a un public au moins amplifie, sinon...

International audience; Mixed-valent iron [Fe(II)-Fe(III)] minerals such as magnetite and green rust have received a significant amount of attention over recent decades, especially in the environmental sciences. These mineral phases are intrinsic and essential parts of biogeochemical cycling of metals and organic carbon and play an important role regarding the mobility, toxicity, and redox transformation of organic and inorganic pollutants. The formation pathways, mineral properties, and applications of magnetite and green rust are currently active areas of research in geochemistry, environmental mineralogy, geomicrobiology, material sciences, environmental engineering, and environmental remediation. These aspects ultimately dictate the reactivity of magnetite and green rust in the environment, which has important consequences for the application of these mineral phases, for example in remediation strategies. In this review we discuss the properties, occurrence, formation by biotic as well as abiotic pathways, characterization techniques, and environmental applications of magnetite and green rust in the environment. The aim is to present a detailed overview of the key aspects related to these mineral phases which can be used as an important resource for researchers working in a diverse range of fields dealing with mixed-valent iron minerals.

The ammonium cation interaction with Na-birnessite in aqueous alkaline medium was studied. Solution and solid analysis give evidence that birnessite is not only acting as a cationic exchanger toward NH4+. The surface analysis performed by XPS showed that N1s spectra are characterized by the existence of two different environments: one assignable to an interlayer NH4+ and the second to a chemisorbed N-species. Structural and chemical transformations were observed on birnessite with nitrogen mass balance deficit. The monitoring of NH4+, Na+, Mn2+, NO3- and NO2- and solid changes (average oxidation state of Mn, cation exchange capacity, solid nitrogen content and symmetry evolution identified by XRD and FTIR) indicate unambiguously that NH4+ reacts chemically with the birnessite.

Bienveillante ou non, la lecture de l’article du sociologue Eric Maigret (2013) oblige a se poser deux series de questions. La premiere concerne l’ordre d’exposition privilegie par l’auteur et la defense et illustration des cultural studies entreprise par lui. La seconde concerne les classifications mises en œuvre. Il n’empeche, il s’avere aussi que, du point de vue philosophique qui est le notre, son article reveille des questions centrales posees par et dans notre travail portant sur la constitution de soi comme « spectateur » dans une histoire culturelle europeenne du spectateur, et la critique des assignations esthetiques. Relevant d’un champ d’etudes desormais de plus en plus important, ce travail ne se preoccupe pas de savoir s’il releve de la science ou non, ou de quelque modele de scientificite. Il se preoccupe plutot d’essayer de faire voir, avec circonspection, ce que nous pensons etre un element de discussion neglige dans le champ des sciences, de la politique et de l’art, la question du sensible.

The new mineral mössbauerite (IMA2012−049), Fe63+O4(OH)8[CO3]·3H2O, is a member of the fougèrite group of the hydrotalcite supergroup. Thus, it has a layered double hydroxide-type structure, in which brucite-like layers [Fe63+O4(OH)8]2+ are intercalated with CO32− anions and water molecules. Mössbauerite is the fully oxidized analogue of fougèrite and trébeurdenite, related to them chemically by the exchange of (Fe3+O2−) with (Fe2+OH−). Mössbauerite, intimately intergrown with trébeurdenite, was discovered in intertidal gleys from Mont Saint-Michel Bay, France, along with quartz, feldspars and clay minerals. Mössbauerite is formed by the oxidation of the other members of the fougèrite group. Like them, it occurs as μm-scale platelets in gleys with restricted access to atmospheric O and decomposes rapidly when exposed to air. Identification and characterization of these minerals has relied on an electrochemical study of synthetic analogues and Mössbauer spectroscopy, which inspired the name of the new mineral.Unlike fougèrite and trébeurdenite, which are blue-green, pure synthetic mössbauerite is orange in colour. Detailed optical and other physical properties could not be determined because of the small platelet size and instability. The hardness is probably 2−3, by analogy with other members of the supergroup and the density, calculated from unit-cell parameters, is 2.950 g/cm3. Synchrotron X-ray data indicate that the natural material is a nanoscale intergrowth of 2T and 3T polytypes; the latter probably has the 3T7 stacking sequence. The corresponding maximum possible space group symmetries are Pm1 and P3m1. Unit-cell parameters for the 3T cell are a = 3.032(7) Å, c = 22.258(4) = 367.420 Å and Z = ½.Mössbauer spectroscopy at 78 K indicates that two distinct Fe3+ environments exist in a 2:1 ratio. These are interpreted to be ordered within each layer, but without the development of a threedimensional superlattice. Mössbauerite undergoes gradual magnetic ordering at 70−80 K to a ferromagnetic state, below which it splits into three sextets S1m, S2m and S3m, as measured at 15 K, and shows the same intensity ratio ½:⅙:⅓ as the three doublets for fougèrite D1f, D2f, D3f in the paramagnetic state at 78 K. This suggests that there is also short-range coupling of interlayer carbonate anions with respect to the octahedral layers and that the 2D long-range order of carbonates in interlayers remains unchanged.

International audience; The objective of this study was to characterize phosphate adsorption onto synthetic 2-lines ferrihydrite using surface analysis by X-ray Photoelectron Spectroscopy and batch experiments. Surface analysis of ferrihydrite samples before phosphate sorption gives very reproducible Fe:O surface ratios of (1:3 +/- 0.1). Phosphate sorption onto ferrihydrite was investigated by means of pH, initial phosphate concentration, and ionic strength effects. Additionally, potential background electrolyte influence on phosphate adsorption was also determined. Phosphate uptake by ferrihydrite significantly increases with decreasing pH, with a maximum uptake of 104.8 mg PO4 g(-1) obtained at pH = 4. Phosphate removal increases with the enhancement of ionic strength in agreement with the formation of inner-sphere complexes. The presence of chloride, nitrate, and sulfate showed no competing effect on phosphate removal efficiency. Sorption kinetics follow a pseudo-second order model (R-2 > 0.99) and the Freundlich isotherm model adequately describes sorption (R-2 = 0.995). The careful examination of high resolution Fe 2p, O 1s, and P 2p spectra before and after phosphate sorption allows the characterization of the modifications occurring onto the ferrihydrite surface. The binding energy of the P 2p peak agrees well with that observed in Fe-PO4 compounds. Additionally, binding energy shifts in the Fe 2p spectra combined to variations in the relative intensity of the components in the high resolution O 1s spectra illustrate well the formation of chemical bonding between iron and phosphate anions at the ferrihydrite surface.

Quelles fins vise l’introduction d’une education artistique a l’ecole ? Selon la reponse donnee a cette question, ce sont des voies d’enseignement differentes qui se profilent. Si l’on choisit d’eviter les anciennes visees du consensus, et si l’on refuse de se contenter d’en faire la critique, comment reorienter le debat ? L’article propose de focaliser un tel enseignement sur la parole suscitee par les œuvres, dans la mesure ou elle temoigne de trajectoires de spectateurs aspirant a des compositions avec les autres.

International audience; The annual population growth rate of African cities is on average 5 %. This situation leads to increasing quantities of wastewater generated in most cities. For example, in the Ivorian capital Abidjan, the daily volume of collected wastewater is actually ~ 190 000 m 3. The Abidjan wastewaters only undergo a passive treatment prior to discharge into the Ebrié lagoon. Moreover, excess of orthophosphate is at the origin of eutrophication that leads to strong perturbation of the lagoon biodiversity. Therefore, there is a growing interest to identify easily available minerals for performing tertiary treatment of dephosphatisation [1]. In this study, samples of shale were collected from Toumodi region (i.e. Lomo North site) in the Center of Ivory Coast. The solid samples were characterized by several techniques including XRD, Mössbauer spectroscopy, SEM-EDX, XPS and ICP-MS. The major minerals of the shale are silicates and phyllosilicates, i.e. quartz, albite, muscovite and clinochlore. Structural Fe III and Fe II species are present in substitution of other cations of the clays minerals and a minor part of the Fe III species is present in goethite -FeOOH. The reactivity of the shale with phosphate (PO 4) was studied in both homogeneous suspension (" batch reactor ") and in hydrodynamic conditions (" column reactors "). A particular attention was devoted to determine both residual phosphate and metal species (Ca 2+ , Mg 2+ , Al 3+ and total iron) released in solution after phosphate sorption. Kinetics experiments in " batch reactors " showed that the saturation of the shale surface by PO 4 occurred after  24 hours of contact time. Adsorption isotherms led to a maximal PO 4 adsorption capacity of  0.4 mg g-1 at neutral pH. The PO 4 removal capacity decreased with increasing pH and reached a minimum around pH= 10. In strong alkaline conditions an increase of the PO 4 removal capacity was observed that was linked to an increase of the aluminum solubility. During the column experiments, the phosphate solution circulated continuously during a five days period and then was stop during 2.7 days to study the effect of residence time on phosphate removal. This sequence was repeated several times in order to reach a quasi-saturation of the column by PO 4. The PO 4 breakthrough of the column was strongly dependent on the contact time. Interestingly, a correlation between the increase of PO 4 removal rate observed at longer contact time with an increase of Ca 2+ and Mg 2+ solubility was established. Therefore, these species could play a more important role than iron in the PO 4 removal mechanism of shale. In conclusion the shale of Ivory Cost is an interesting material for PO 4 removal from wastewater. Nevertheless, it should be compared in terms of removal efficiency and cost to other readily available natural compounds, e.g. laterite and sandstone, or recently developed synthetic Fe III nanocomposites [2]. [1] Kõiv, M., Bavor, H.J., Chazarenc, F., Mander, Ü. (2011) Filter materials for phosphorus removal from wastewater in treatment wetlands-A review. Ecological Engineering, 37(1), 70-89. [2] Ruby, C. Barthélémy, K., Hanna, K. Mallet, M. Naille, S. (2015) Synthesis process and hydrodynamic behavior of a new filtration material for passive wastewater dephosphatation, Materials and Design, 86, 168-177.

Ruby Christian. L'émancipée / L'émancipé ! Mais quelle émancipation ?. In: Raison présente, n°185, 1er trimestre 2013. Émancipation plurielles. pp. 69-76.

Ruby Christian. Radioscopie de l'approche du spectateur d'art. In: Raison présente, n°187, 3e trimestre 2013. Figures de spectateur. pp. 17-26.

International audience; Background: The activated sludge treatments combined to the addition of ferric chloride is commonly used to eliminate nitrate and phosphate from waste water in urban area. These processes that need costly infrastructures are not suitable for rural areas and passive treatments (lagoons, reed bed filters…) are more frequently performed. Reed bed filters are efficient for removing organic matter but are not suitable for treating phosphate and nitrate as well. Passive water treatments using various materials (hydroxyapatite, slag…) were already performed, but those allowing the elimination of both nitrate and phosphate are not actually available.Methods: The goal of this work is to identify the most suitable iron based materials for such treatments and to determine their optimal use conditions, in particular in hydrodynamic mode. The reactivity of the iron based minerals was measured either by using free particles in suspension or by depositing these particles on a solid substrate.Results: Pozzolana, a volcanic rock, that is characterized by a porous sponge-like structure suits for settling a high amount of iron oxides. In addition, the experimental conditions enabling to avoid any ammonium formation when green rust encounters nitrate were also determined within the framework of a full factorial design. The dephosphatation and denitrification process is divided into two steps that will be performed inside two separated reactors. Indeed, the presence of phosphate inhibits the reduction of nitrate by green rust and the dephosphatation process must precede the denitrification process.Conclusion: In order to remove phosphate, ferrihydrite coated pozzolana is the best materials. The kinetics of reaction of green rust with nitrate is relatively slow and often leads to the formation of ammonium. In this process, it is interesting to favor the accumulation of nitrite in a first step, these species react much more quickly with green rust and do not transform into ammonium.