As Terras Raras (TRs), particularmente a série dos lantanídios, são consideradas elementos estratégicos da tecnologia moderna devido ao seu papel essencial na catálise petroquímica, lasers, materiais luminescentes, e na fabricação de superimãs necessários para conversão de energia em carros elétricos e geradores eólicos. Atualmente, o comércio internacional de TRs é dominado pela China (> 90%). O Brasil apresenta um enorme potencial em termos de reservas de TRs, mas o país ainda carece de uma tecnologia competitiva para o processamento mineral, incluindo a separação e produção de elementos. Processos hidrometalúrgicos baseados na extração por solvente e troca iônica são normalmente empregados pelos produtores, mas os processos são bastante caros e poluentes, envolvendo centenas de reatores e colunas para superar as propriedades químicas muito similares dos elementos. Esta tese relata uma tecnologia alternativa verde chamada Nanohidrometalurgia Magnética (NHMM), que faz parte dos nossos esforços para introduzir a nanotecnologia na área mineral. A tecnologia é baseada em nanopartículas superparamagnéticas, previamente projetadas com um revestimento protetor e um agente complexante específico, como o DTPA, para sequestrar os elementos estratégicos da solução lixiviada. NHMM permite a captura e processamento de elementos metálicos diretamente a partir de solução aquosa, sem empregar solventes orgânicos. Depois de confinar o elemento com o uso de um ímã externo (Nd2Fe14B), ele pode ser facilmente separado da mistura e liberado pela aplicação de condições ácidas leves, enquanto as nanopartículas magnéticas retornam ao processo, para um novo procedimento em lote. Na escala laboratorial, todo o procedimento pode ser realizado no mesmo reator, cumprindo, além das instalações de processamento e recuperação, os requisitos mais importantes da Química Verde. Esta tese foi concentrada na extração e separação de elementos de lantanídios da monazita. Um estudo detalhado termodinâmico e cinético foi realizado para compreender o processo. O intrigante comportamento magnético das nanopartículas magnéticas revestidas de lantanídios também foi investigado, fornecendo um ensaio crítico de seu comportamento magnetoforético em solução aquosa. O comportamento magnetoforético das nanopartículas superparamagnéticas permitiu monitorar sua interação direta com os íons lantanídeos, ilustrando uma nova perspectiva no processo de separação. / Rare earths (RE), particularly the lanthanide series, are considered strategic elements in modern technology because of their essential role in petrochemical catalysis, lasers, luminescent materials, and in the fabrication of strong magnets required for energy conversion in electric cars and aeolic generators. Currently, the international RE commerce is dominated by China (> 90%). Brazil exhibits a huge potential in terms of RE reserves but the country still lacks a competitive technology for mineral processing, including the element separation and production. Hydrometallurgy processes based on solvent extraction and ionic exchange are normally employed by the producers, but the processes are rather expensive and polluting, involving hundred reactors and columns to overcome the challenge of dealing with elements exhibiting very similar chemical properties. This thesis reports an alternative green technology named Magnetic Nanohydrometallurgy (MNHM), reinforcing our attempts and efforts to introduce Nanotechnology in the mineral area. The MNHM technology is based on superparamagnetic nanoparticles, previously engineered with a protecting coating and a specific complexing agent, such as DTPA, for sequestering the strategic elements from the lixivia solution. MNHM allows the capture and processing of metal elements directly from aqueous solution, without employing organic solvents. After confining the element with the use of an external magnet (Nd2Fe14B), it can be easily separated from the mixture, and released by applying mild acidic conditions, while the magnetic nanoparticles return to the process, for a new batch procedure. At the laboratory scale, the entire procedure can be performed in the same reactor, fulfilling, in addition to the processing and recovery facilities, the most important requisites of Green Chemistry. This thesis was concentrated on the extraction and separation of lanthanide elements from monazite. A detailed thermodynamic and kinetic study was carried out to support the ideas, leading to a new separation technology, capable of obtaining and processing the lanthanides under green and sustainable conditions. The magnetophoretic behavior of the superparamagnetic nanoparticles allowed to monitor their direct interaction with the lanthanide ions, illustrating a new perspective in the separation process.

Les travaux de cette thèse concernent la compréhension à l'échelle atomique des processus physico chimiques intervenant aux interfaces et dans des phases diluées. Pour commencer, nous avons étudié l'interaction entre la molécule 1,4-diazabicyclo [2.2.2]octane (DABCO) et un atome de gaz rare (He, Ne, Ar, Kr). Nous avons effectué une analyse systématique de ces systèmes, et nous en avons conclu que la méthode MP2 associée à une base diffuse est suffisamment précise pour décrire le système DABCO – Ar. Les surfaces d'énergie potentielle des complexes DABCO – gaz rare ont été calculées, ce qui nous a permis de réattribuer les spectres expérimentaux de ces espèces. Ensuite, nous nous sommes concentré sur les complexes DABCO – Arn (avec n = 2, 3, 4) neutres et ioniques. Nous avons montré que le DABCO interagi avec les atomes d'argon, et subit des déformations dues à l'effet de cette interaction faible sur ses modes de vibration. Par la suite, nous avons étudié les plus bas états électroniques du DABCO – Arn (n = 1, 2, 3). Nos résultats pourront être étendus à l'interprétation qualitative des études spectroscopiques et dynamiques des molécules de DABCO absorbés dans de grands agrégats d'argon. Enfin, nous avons étudié l'interaction entre l'imidazole et une couche d'or en présence de CO2. Nous avons montré que la molécule d'imidazole se fixe à l'agrégat d'or par une liaison covalente entre l'atome d'azote et un atome d'or, ainsi que des interactions faibles de type van der Waals entre les atomes d'hydrogène et la surface d'or. Nous avons déterminé que le site préférentiel pour l'interaction imidazole – or est le site top. Cette interaction permet un transfert de charge de l'imidazole vers la surface d'or, ce qui affecte la capture du CO2 (environ 50% plus faible par rapport à l'interaction Im(seule) – CO2). Mais l'augmentation du nombre de molécules d'imidazole à la surface de la couche d'or pourrait permettre une liaison plus forte entre le CO2 et l'imidazole / This thesis concern the understanding at the atomic level of physicochemical processes occurring at interfaces and dilute phases. First, we studied the interaction between the 1,4- diazabicyclo [2.2.2] octane (DABCO) molecule and a rare gas atom (He, Ne, Ar, Kr). We conducted a systematic analysis of these complexes, and we concluded that the MP2 method with a diffuse basis set is accurate to describe the system DABCO – Ar. The potential energy surfaces of DABCO – rare gas complexes were calculated, which allowed us to reatribuate the experimental spectra of these species. Then, we focused on DABCO – Arn (n = 2, 3, 4) neutral and ionic clusters. We have shown that the DABCO interacted with argon atoms and undergoes deformation due to the effect of the weak interaction on his vibrational modes. Subsequently, we studied the lowest electronic states of DABCO – Arn (n = 1, 2, 3). Our results can be extended to the qualitative interpretation of spectroscopic and dynamic studies of absorbed DABCO in large argon clusters. Finally, we studied the interaction between imidazole and a gold surface with CO2. We have shown that the imidazole molecule binds to the gold surface by a covalent bond between the nitrogen atom and a gold atom, and van der Waals interactions between hydrogen atoms and the gold surface. We determined that the preferred site for the imidazole – gold interaction is the top site. This interaction allows a charge transfer from the imidazole to the gold surface, which affects the capture of CO2 (about 50% lower compared to the interaction Im – CO2). But increase number of imidazole molecules on the gold surface could lead to a stronger bond between CO2 and imidazole

La perte auditive est le trouble sensoriel le plus commun avec 40 % des personnes de plus de 65 ans affectées, entraînant, chez ces patients une dégradation de leur qualité de vie et un isolement sociale. Les principales causes sont le vieillissement ou l'exposition au bruit, mais les mutations génétiques sont aussi à l'origine de déficits auditifs. Parmi ces surdités, le Syndrome de Chudley McCullough (CMCS) est une maladie rare caractérisée par une surdité sévère et précoce associée à des anomalies cérébrales (Chudley et al., 1997). Récemment, des mutations du gène GPSM2 (G protein signaling modulator 2) ont été décrites comme étant responsables de cette pathologie sans que l'on en connaisse les mécanismes (Walsh et al., 2010). A l'aide d'un modèle d'étude murin de cette pathologie, nous avons identifié les bases moléculaires de la pathologie ainsi qu’une nouvelle fonction moléculaire pour Gpsm2 sur la modulation du cytosquelette d’actine. La perturbation de cette fonction affect à la fois la maturation des cellules auditives et la croissance des jeunes neurones, pouvant expliquer les surdités et l’hypoplasie du corps calleux décrits chez ces patients (Mauriac et al., 2017). De plus, nous avons identifié les partenaires de Gpsm2, les protéines Gαi, comme indispensables à la fonction auditive (Beer-Hammer et al., 2018). Au niveau moléculaire, nous avons découvert une nouvelle interaction de Gpsm2 avec une protéine essentielle à la maturation des cellules auditives et impliquées dans les surdités de type Usher, la Whirlin.Par conséquent, notre étude a permis de clarifier l’étiologie du CMCS et de montrer que sa complexité et son aspect multisyndromique sont dus au rôle multifonctionnel du complexe Gpsm2/G⍺i non seulement sur la dynamique de la tubuline dans des cellules en prolifération et en post-mitotiques (Ezan et al., 2013), mais aussi sur la dynamique d’actine (Mauriac et al., 2017). / Hearing loss is the most common sensory disorder, affecting 40% of people over 65 years old, leading for these patients, to the deterioration of their quality of life and to their social isolation. The main causes are aging or exposure to noise. However, many genes can also cause deafness. Among these deafnesses, the Chudley McCullough Syndrome (CMCS) is a rare disease characterized by severe and early deafness associated with brain abnormalities (Chudley et al., 1997). Recently, mutations in the GPSM2 (G protein signaling modulator 2) gene were found to be causative of this pathology, but the molecular basis were unknown (Walsh et al., 2010). Using a murine model of this pathology, we identified the molecular basis of this pathology as well as a new molecular function for Gpsm2 on the modulation of actin cytoskeleton. The disruption of this function leads to defect of the maturation of auditory hair cells and the reduction of the outgrowth of young neurons which may explain the deafness and the hypoplasia of the corpus callosum described in these patients (Mauriac et al., 2017). In addition, we identified partners of Gpsm2, Gαi proteins, as essential for auditory function (Beer-Hammer et al., 2018). At the molecular level, we have discovered a new interaction of Gpsm2 with a protein essential for the maturation of auditory cells and involved in Usher type deafness, Whirlin.Therefore, our study clarified the etiology of CMCS and show that the complexity and multisyndromic aspect of this pathology is due to the multifunctional role of the complex Gpsm2/G⍺i not only on tubulin dynamics in proliferating cells and post-mitotic cells (Ezan et al., 2013), but also on actin dynamics (Mauriac et al., 2017).

Graduation date: 1998

Rare-earth oxides used in oxide dispersion strengthening are known to provide excellent strength and deformability over ordinary dispersion strengthening. It has been suggested that this may be due to the development of molybdate compounds instead of pure dispersed oxide particles. These alloys are produced by dispersing particles of certain rare-earth oxides in a molybdenum matrix and forming the mixture into a composite ingot. During the high-temperature consolidation process, the oxides are converted into rare-earth molybdates. With subsequent processing, these molybdate phases undergo deformation to form high-surface-area ribbons that serve to inhibit dislocation movement, thus improving the mechanical properties of the molybdenum matrix. It is still unknown what specific compounds, phases, and crystal structures provide these metal-oxides with their high strength and deformability. Because the molybdate phases are formed at high temperatures and low oxygen partial pressures, little is also known of the high-temperature phase equilibria of the REO-Mo systems under these conditions. The primary goal of this study was to deifine phase equilibria on systems of Mo with rare-earth oxides. The project aimed to identify compounds, phases, and specific oxidation states of molybdenum at various processing conditions. Systems of LaO1.5-MoOx, YO1.5-MoOx, and ZrO2- MoOx were investigated at temperatures of 1000??nd 1200??and O2 partial pressures ranging from 10-4 Pa to 10-13 Pa. Samples were prepared using powder starting materials of Mo and rare-earth oxides were combined in stoichiometric ratios. The samples were then electrically heated in a ceramic tube furnace in which the oxygen partial pressure was controlled by means of a combined flow of H2 and CO2 gas. Characterization was performed using x-ray diffraction, with published powder diffraction files for phase identification.

Thesis (M.S.)--North Carolina State University, 2003. / Title from PDF t.p. (viewed on Dec. 8, 2005). Vita. Includes bibliographical references (p. 97-103).

Thesis (Ph.D.)--McMaster University (Canada), 1990. / Source: Dissertation Abstracts International, Volume: 62-13, Section: A, page: 0000.

Thesis (M.S.)--University of Tennessee, Knoxville, 2004. / Title from title page screen (viewed Feb. 2, 2005). Thesis advisor: Randall L. Small. Document formatted into pages (viii, 73 p. : ill. (some col.), maps). Vita. Includes bibliographical references (p. 39-44).

Thesis (Ph. D.)--Montana State University--Bozeman, 2003. / Typescript. Chairperson, Graduate Committee: Rufus L. Cone. Includes bibliographical references (p. 361-380).

Thesis (M.E.S.)--Evergreen State College, 2009. / "June 2009." Title from title screen (viewed 4/8/2010). Includes bibliographical references (leaves 26-32).