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Extraction, caractérisation, réactivité chimique des substances humiques naturelles avec les phosphates de Hahotoe-Kpogame et leurs propriétés photodégradantes

Abstract : The need to increase agricultural yields has been leading to widespread and intensive utilization of agrochemicals for soil fertilization and plants protection as well. Irrational use of these various chemicals causes pollution of soil, surface water bodies and ground water. For this reason, the search for green fertilizers and the assessment of the behaviour and fate of organic pollutants in soil have become major research topics. It was in this regard that the present work was undertaken. In step one of this work, natural humic substances extracted from a soil sample in Lomé (AHSL, AFSL), Badou (AHSB, AFSB) and from a compost sample (AHC, AFC). Were characterized through chemical analysis and by physicochemical methods including ultraviolet and visible rays absorption, Electronic scan microscopy and Infra Red spectroscopy. Results of these different characterizations proved the organic and humic characters of these samples. In the second step of the work, dissolution of rock phosphates of Hahotoé - Kpogamé (Togo) by in solutions of conventional mineral and organic acids and natural humic substances as well was carried out. The results showed that: - dissolution of apatite in strongly acid solutions was due to the phosphate rock attack by hydronim ions. That was the only dissolution effect by mineral acidic solutions; - dissolution of the phosphate ore in slightly acidic and alkaline organic solutions was due to the complexation of the metal ions (Ca 2+) by the functional groupings. The mechanism of this dissolution was evidenced by conductimetric and potentiometric measurements. The complexing capacity of these solutions increased with increasing of pH. Metal ions in general and calcium in particular complexing by humic substances may serve as a method to elaborate new types of organic fertilizers from biodegradable organic matter and rock phosphate. Continuing the investigation of the reactivity of humic substances, the third and last step of this work is dealing with the assessment of the ability of humic substances to photodegrade organic pollutants. Experimental results clearly showed that these substances were effective inductors of pollutant photodegradation under solar excitation. This photodegradation was due to the formation of reactive species by organic matter like oxygen singlet, hydroxyl radicals and triplet excited states. As an application of these experimental findings, the photodegradation by humic substances of Profenofos ((O-4-bromo-2-chlorophenyl) O-ethyl S-propylphosphorothioate), an organochlorinated polluting pesticide used in the cotton cultivation in Togo was carried out. Physicochemical analysis realised after reaction showed the effective transformation of the pollutant. This transformation was slow in deoxygenized humic solutions in the presence of propan-2-ol which traps hydroxyl radicals generated by humic substances under irradiation. A reasonable conclusion was that these radicals were responsible for the pollutant photodegradation. Identification of intermediates under the various experimental conditions helped us propose chemical structures for the detected photodegadation products.
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  • HAL Id : tel-00719333, version 1

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Moursalou Koriko. Extraction, caractérisation, réactivité chimique des substances humiques naturelles avec les phosphates de Hahotoe-Kpogame et leurs propriétés photodégradantes. Chimie organique. Université Blaise Pascal - Clermont-Ferrand II; Université de Lomé, 2010. Français. ⟨NNT : 2010CLF22023⟩. ⟨tel-00719333⟩

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