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Abattement des phosphates des eaux usées par adsorption sur des géomatériaux constitués de Latérite, grès et schistes ardoisiers

Abstract : Wastewaters are often loaded in phosphate from human activities. The discharge of such wastewater without adequate treatment leads to rapid eutrophication of water bodies. The main of the present thesis was to characterize and investigate the removal efficiency of phosphate from water by natural geological material available in large amount in Ivory Coast. Ultimately, it has ambition to valorize geological material without mining interest for environmental purposes. For this research, the laterite, sandstone and shale were selected and prepared by mechanical crushing to obtain fine fractions below 80 µm. Detailed study to characterize these three rocks powder was performed, thus several mineralogical and physico-chemical properties were determinated by means of : X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), N2-adsorption/desorption techniques (BET), energy dispersive x-ray spectroscopy (EDX), particle size distribution, cation exchange capacity and chemical analyses by atomic emission spectrometry (ICP-AES) and mass spectrometry (ICP-MS). Data shows high percentages of iron, aluminum and calcium oxides and oxyhydroxides for these three materials. This composition confer to the fine fraction the specific surface of 34; 4.7 et 16.5 m2/g for laterite, sandstone and shale respectively. In addition, the mineral structures of these materials reveal the presence of meso-and microporosity. These materials were then evaluated in the batch treatment of synthetic liquid effluents containing pure KH2PO4. The optimal dosage and equilibrium times were detected. After, isotherms were built at 20, 30 and 40°C. It was shown that phosphate affinity for the three absorbents is more important for laterite, sandstone and shale. The absorption process is strongly depends on pH. Phosphate retention rate on sandstone seem not to depend on temperature, on the other hand, those of laterite increase on the contrary way of the temperature and vice versa for schist. Several kinetic models (pseudo first order, pseudo second order, Elovich and diffusion models) were evaluated as well as thermodynamic parameters. Absorption reactions are perfectly described by the pseudo second order. Absorption equilibrium data allow defining interval where Langmuir and Freundlich model seems perfect. The proposed retention mechanism suggests the existence of two kinds of sites. DRIFTS analyses of adsorbents after adsorption revealed chemical interaction on adsorption process onto laterite and sandstone. This study demonstrated that laterite, sandstone and shale are an effective adsorbent for phosphate removal from aqueous solution. However, laterite shows a strong potentiality compared to the two others adsorbents
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Sandotin Lassina Coulibaly. Abattement des phosphates des eaux usées par adsorption sur des géomatériaux constitués de Latérite, grès et schistes ardoisiers. Autre. Université de Lorraine, 2014. Français. ⟨NNT : 2014LORR0065⟩. ⟨tel-01751154⟩

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