Síntesis, caracterización y evaluación de la reactividad de nanopartículas de hierro cerovalente u óxidos de hierro nanoparticulados para el tratamiento de uranio hexavalente en agua
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Comisión Nacional de Energía Atómica. Instituto de Tecnología Sabato
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Tesis para optar al título de Magister en Ciencia y Tecnología de Materiales
In this Thesis, the synthesis, characterization and use of iron nanoparticles for U(VI) removal in aqueous systems was studied. U(VI) treatment in aqueous solution and its transformation in less toxic or easily removable products is a relevant aspect for studies related to the nuclear activity. Particularly, U(VI) removal employing iron nanomaterials is a relevant subject in the literature, but which needs still more detailed studies for its optimization. Furthermore, it is very important the characterization of iron nanomaterials, commercial and prepared in the laboratory as well, with the aim at understanding the processes involved in the removal reactions, together with the comparison of the efficiency of the different materials, especially in order to a potential application for remediation of real waters. First, the synthesis of zerovalent iron nanoparticles (nZVI) was performed in the laboratory, following a widely known procedure, by reducing a Fe(III) salt using sodium borohydride in anoxic atmosphere. Two different experimental setups were tested. The first setup consisted in three coupled modules, with the main reactor being a round-bottom flask, and reagents being inserted through a rubber cap, stirred by an orbital shaker. The second setup consisted in only one module, a jacketed reactor with a PTFE gas tight lid and mechanical stirring, which allowed simplifying the design. This method is still under development, and the optimization of the process is underway. Subsequently, the complete characterization of nanoparticles was performed, in order to know their structural and compositional properties, by using transmission electronic microscopy (TEM), X-ray diffraction (XRD), porosimetry, Raman, XANES and Mössbauer spectroscopies. Additionally, commercial nanoparticles used for removal experiments were characterized by the same techniques. The characterization of both synthesized and commercial materials, in order to elucidate the exact composition of the nanoparticles and to understand the removal mechanisms, is planned for future works. U(VI) removal in aqueous solution by using commercial nZVI and nanomagnetite (nM) was performed in batch experiments with the same U(VI) initial concentration and a range of nanoparticles initial concentration (molar ratio (MR) Fe:U = 1 - 100 for nZVI and MR Fe:U = 4 for nM), in anoxic conditions. Two different anoxicity levels were tested, dissolved oxygen (DO) > 0,1 mg L-1 and DO < 0,1 mg L-1, reached by modifying the setup arrangement. Analysis of species in solution was performed to evaluate the matching with possible mechanisms described in literature. While the results are very good, it is expected in future works to optimize the removal to achieve the allowed levels of U (VI) and Fe regulated in water for diverse applications. Removal experiments using the nZVI synthesized in the laboratory are also pending. Removal experiments employing nZVI under UV-Vis irradiation, and preliminary U(VI) and Cr(VI) joint removal experiments using nZVI have been also studied. The results were encouraging and represent a potential investigation line to continue improving the U(VI) removal systems. In all cases, the solid products obtained after the removal experiments were analyzed by the solid characterization techniques cited before, and preliminary X-ray photoelectron spectroscopy (XPS) analyses were made. Complementary studies of characterization in order to determine with greater accuracy the composition of nanoparticles after the experiments, mainly regarding the uranium oxidation state, are envisaged.
In this Thesis, the synthesis, characterization and use of iron nanoparticles for U(VI) removal in aqueous systems was studied. U(VI) treatment in aqueous solution and its transformation in less toxic or easily removable products is a relevant aspect for studies related to the nuclear activity. Particularly, U(VI) removal employing iron nanomaterials is a relevant subject in the literature, but which needs still more detailed studies for its optimization. Furthermore, it is very important the characterization of iron nanomaterials, commercial and prepared in the laboratory as well, with the aim at understanding the processes involved in the removal reactions, together with the comparison of the efficiency of the different materials, especially in order to a potential application for remediation of real waters. First, the synthesis of zerovalent iron nanoparticles (nZVI) was performed in the laboratory, following a widely known procedure, by reducing a Fe(III) salt using sodium borohydride in anoxic atmosphere. Two different experimental setups were tested. The first setup consisted in three coupled modules, with the main reactor being a round-bottom flask, and reagents being inserted through a rubber cap, stirred by an orbital shaker. The second setup consisted in only one module, a jacketed reactor with a PTFE gas tight lid and mechanical stirring, which allowed simplifying the design. This method is still under development, and the optimization of the process is underway. Subsequently, the complete characterization of nanoparticles was performed, in order to know their structural and compositional properties, by using transmission electronic microscopy (TEM), X-ray diffraction (XRD), porosimetry, Raman, XANES and Mössbauer spectroscopies. Additionally, commercial nanoparticles used for removal experiments were characterized by the same techniques. The characterization of both synthesized and commercial materials, in order to elucidate the exact composition of the nanoparticles and to understand the removal mechanisms, is planned for future works. U(VI) removal in aqueous solution by using commercial nZVI and nanomagnetite (nM) was performed in batch experiments with the same U(VI) initial concentration and a range of nanoparticles initial concentration (molar ratio (MR) Fe:U = 1 - 100 for nZVI and MR Fe:U = 4 for nM), in anoxic conditions. Two different anoxicity levels were tested, dissolved oxygen (DO) > 0,1 mg L-1 and DO < 0,1 mg L-1, reached by modifying the setup arrangement. Analysis of species in solution was performed to evaluate the matching with possible mechanisms described in literature. While the results are very good, it is expected in future works to optimize the removal to achieve the allowed levels of U (VI) and Fe regulated in water for diverse applications. Removal experiments using the nZVI synthesized in the laboratory are also pending. Removal experiments employing nZVI under UV-Vis irradiation, and preliminary U(VI) and Cr(VI) joint removal experiments using nZVI have been also studied. The results were encouraging and represent a potential investigation line to continue improving the U(VI) removal systems. In all cases, the solid products obtained after the removal experiments were analyzed by the solid characterization techniques cited before, and preliminary X-ray photoelectron spectroscopy (XPS) analyses were made. Complementary studies of characterization in order to determine with greater accuracy the composition of nanoparticles after the experiments, mainly regarding the uranium oxidation state, are envisaged.