Interaction entre des matériaux argileux et un milieu basique riche en calcium

Les matériaux argileux peuvent être utilisés dans le domaine cimentaire pour leur effet pouzzolanique (après deshydroxylation) ou encore comme charge inerte pour combler en partie la porosité ouverte. L étude des interactions entre les produits cimentaires et les argiles est donc essentielle pour optimiser la valorisation de ces matériaux. Les interactions entre trois argiles (kaolin, illite et montmorillonite) et une solution d hydroxyde de calcium Ca(OH)2) ont donc été étudiées. Les résultats obtenus montrent que toutes ces argiles pie gent simultanément les ions calcium et hydroxyle. Cette adsorption est fonction de la surface spécifique de l argile et de la basicité de la solution. Le calcium se révèle être un coagulant pour le kaolin et un dispersant pour l illite en milieu basique. Le cas de la montmorillonite est plus complexe du fait d échange interfoliaire. Les résultats ont pu être interprétés en prenant en compte le caractère donneur ou accepteur des atomes des diverses surfaces et le omportement de la sphère d hydratation des ions calcium. L utilisation de dispersants organiques est également présentée.Clay materials can be used in cementitous materials for their pozzolanic effect (after deshydroxylation) or like inert load to partly fill open porosity. The study of interactions between the cement based materials and clays is thus essential to optimise the valorisation of these materials. Surface reactivity of three clays (kaolin, illite and montmorillonite) in calcium hydroxide based dispersions (Ca(OH)2) was thus studied. The results obtained show that all these clays trap simultaneously calcium and hydroxyl ions. This adsorption is a function of the specific surface of clay minerals and the alkalinity of the dispersion. The calcium proves to be a coagulant for the kaolin and a dispersant for the illite in a basic medium. The case of montmorillonite is more complex because of interfoliar exchange. The results could be interpreted by taking into account the donor or acceptor character of atoms of various surfaces. The effect of organic dispersants is also discussed.LIMOGES-BU Sciences (870852109) / SudocLIMOGES-ENSCI (870852305) / SudocSudocFranceF

Physicochemical characterization of edible clays and release of trace elements

International audienceThe mineralogical composition of seven edible clays from West Africa (Ivory Coast, Guinea and Senegal) was determined by X-ray diffraction, thermal (DTA, TGA and DSC) and chemical (ICP-MS and ICP-OES) analyses and measurement of specific surface areas and density. The major compounds were kaolinite, illite, muscovite, quartz and feldspars. Electrochemical analysis of clay suspensions by voltamperometry (SnO2:F) yielded no results at 6.5 < pH < 7 and pH ≈ 8.3. However, ionic species transfer was revealed at pH ≈ 1.8 by an anodic peak. The analysis by X-ray diffraction of the metal cation layers which were deposited on the blades (SnO2:F), showed the presence of mineral elements having therapeutic implications such as Fe and Zn

Mineralogical and Chemical Characteristics of Clays Consumed in the District of Abidjan (Côte D’Ivoire)

International audienceClay materials of the quarry of Bingerville (district of Abidjan) have been characterized by chemical analysis, X-rays diffraction, infrared spectroscopy and thermal analysis. These materials contain kaolinite (41% - 84%), illite (4% - 10%), quartz (14% - 27%), goethite (2% - 5%) and small amount of rutile (1%) that are not toxic minerals. They also contain some heavy metals which are beneficial to human biological activity (cobalt, copper, molybdenum, zinc) in tiny quantities. Some other heavy metals (lead, cadmium) which are considered as poisonous for human are present in very low content. The samples characterized by relatively fine grains are moderately crystallized. Their specific surface area varied from 26 to 43 m2∙g−1. The mineralogical and physicochemical characteristics of these samples are like ones known for their healing properties. The consumption by internal way of studied materials, although it may be beneficial, requires a sifting to remove coarse grains (ϕ > 2 μm) and a previous microbiological control

Influence of dispersants on the rheological behaviour of kaolin and illite suspensions in concentrated calcium hydroxide medium

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Surface modifications of illite in concentrated lime solutions investigated by pyridine adsorption

International audienceThe surface properties and functionality of an illite-containing clay mineral in alkaline solutions containing increasing quantities of calcium hydroxide were investigated using FTIR monitored pyridine adsorption at various temperatures. Results showed that the binding behavior of electron donor pyridine molecules to illite platelets is mostly governed by electron acceptor sites located at the edges of the clay particles. The binding of bulky hydrated calcium ions at the surface of the illite platelets decreases the surface area of illite. Moderate thermal treatments up to 450 °C do not affect the structure of the clay mineral but strongly decrease the number of Lewis and Brönsted sites available at the edges of the clay platelets

Comparison of surface properties between kaolin and metakaolin in concentrated lime solutions

International audienceThe surface adsorption of calcium hydroxide onto kaolin and metakaolin was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clays to calcium hydroxide solutions of various concentrations. Both clays adsorb calcium and hydroxyl ions but differently. Kaolin adsorbs calcium hydroxide not only at the edges of the clay particles but also onto the basal faces. The adsorbed hydrated calcium ions form a layer on the clay particle surfaces, preventing further dissolution of the clay mineral platelet. Metakaolin shows high pozzolanic activity, which provides the quick formation of hydrated phases at the interfaces between metakaolin and lime solutions. The nature of the hydration products has been investigated using X-ray diffraction (XRD) and differential thermal analysis (DTA). The most important hydrated phases like CSH (hydrated calcium silicate) and C2ASH8 (gehlenite) have been identified

Surface properties of kaolin and illite suspension in concentrated calcium hydroxide medium

International audienceThe adsorption behaviour of calcium hydroxide onto illite and kaolin clay minerals was investigated by monitoring with atomic emission spectroscopy and pH measurements the amounts of ions left in solution after exposing clay minerals to calcium hydroxide solutions of various concentrations. Both clay minerals can adsorb calcium and hydroxyl ions. Rather than just considering proton exchanges at the clay mineral surfaces, the adsorption is explained by an approach based on Lewis description of molecules. With this approach, a mechanism for calcium hydroxide adsorption not only at the edges of the clay particles but also onto the faces is proposed. In order to gain a better insight onto the active groups at the surface of the studied clay minerals, adsorption of pyridine and ammonia on illite and kaolin was followed by FTIR spectroscopy. These measurements gave the signature of edges, which are marginally involved in interactions with calcium ions

Analyse GC-MS des polyphénols totaux extraits des racines de Glyphaea brevis (Spreng.) MONACHINO (Tiliaceae) et évaluation de leur potentiel anti-prolifératif: GC-MS analysis of total polyphenols extracted from the roots of Glyphaea brevis (Spreng.) MONACHINO (Tiliaceae) and assessment of their anti-proliferative activity

International audienceLe terme « cancer » caractérise un large éventail de pathologies impliquant une prolifération cellulaire anormalementimportante et non régulée au sein d’un tissu normal de l’organisme. Les cellules se divisent et se développent demanière incontrôlée, formant des tumeurs malignes et envahissantes des zones proches. Dans cette étude, nous avons montré le potentiel antiprolifératif des polyphénols totaux contenus dans la fraction n-butanol issue des racines de Glyphaea brevis, une plante de la flore ivoirienne, contre les cellules MDA-MB-231, DU145, MDA-MB-435, B16F10. Toutefois, ladite fractionreste inactive contre les cellules HuH7. L’analyse GC-MS a révélé la présence des acides benzoïque, protocatéchique etvanillique dans la fraction d’étude

HPLC Analysis and Cytotoxicity of n-Butanol Extract from Glyphaea brevis Roots Against C6 Glioma Cells

International audienceThe n-butanol extract of the roots of Glyphaea brevis was analysed. HPLC analysis suggested the presence of phenolic compounds like protocatechuic acid (PCA). The extract showed moderate cytotoxic activity against C6 glioma cells (EC50 > 1 mg/ml)

Understanding the strengthening of a lateritic "geomimetic" material

International audienceThe present work aimed to investigate the interactions that control the strengthening of ''geomimetic'' materials. The raw lateritic clay used mainly contained kaolinite, goethite, quartz and hematite. The processing involved a 24 h-reaction with fulvic acid followed by neutralization with lime or with NaOH prior to the curing at 60 C for 18 days under water saturated atmosphere. The compressive strength and thermal conductivity after consolidation were respectively 0.7 MPa and 0.19Wm 1 K 1 for lime-based products, and 0.78 MPa and 0.3Wm 1 K 1 for soda-based products. The latter exhibited low durability in water. Such differences could be related to the high degradation of kaolinite particles when using NaOH, leading to the formation of sodalite, cancrinite and nontronite, which phases did not act as binder. Cementitious CAH and CSH phases were obtained when using lime. Rheological measurements performed on lime-based samples indicated that a shear-thinning behavior prevails up to the 7th day of curing. Above this period, the samples reached a determinant step whereby a solid-like behavior became predominant. The occurrence of binding precursors during the first 7 days of curing conducted to a progressive increase of the yield stress and consistency from 1 to 53 Pa and from 0.2 to 2.3 Pa s, respectively