Le craton archéen de l’In Ouzzal représente une succession d'événements intrusifs et métamorphiques depuis l’Eburnéen qui en font un marqueur important des processus géodynamiques à travers les temps géologiques. La région d’Ihouhaouene située au N-W du terrane de l’In Ouzzal en Algérie est unique de par la présence d’intrusions protérozoïques de carbonatites associées à des roches alcalines saturées. Ces carbonatites intracontinentales comptent parmi les plus anciennes et inhabituelles de par leurs diversités et la présence de minéraux à terres rares. Les carbonatites sont pegmatitiques ou bréchiques avec des fragments de syénite. Elles sont des calciocarbonatites composées de calcite (>50 vol.%), apatite, clinopyroxène et wollastonite et sont associées à des syénites rouges ou blanches présentes sous forme massive. Les syénites sont composées d’alternance de niveaux clairs de feldspaths alcalins rouges ou de wollastonites associées aux feldspaths blancs et de niveaux sombres d’apatites et de clinopyroxènes. Les carbonatites et syénites forment une suite cogénétique caractérisée par une augmentation en SiO2 et une diminution en CaO et CO2. Les carbonatites ont des compositions en silice comprises entre 5 et 35 pds.%, 28 et 53 pds.% CaO et 11 à 36 pds.% CO2. Les syénites montrent une forte teneur en K2O (12 pds.%) et des teneurs très faibles en Na2O (1 pds.%). Les carbonatites et syénites sont riches en éléments incompatibles avec des teneurs en REE supérieures à 7000 fois les chondrites et 1000 fois les chondrites dans les syénites, respectivement, et de fortes teneurs en U, Sr et Th. Les éléments en trace dans les minéraux magmatiques (apatite et pyroxène) mettent en évidence des processus complexes à l’origine de ces roches impliquant plusieurs étapes de cristallisation fractionnée et d’immiscibilité à partir d’un magma mélilititique riche en CO2. Les minéraux des carbonatites riches en silice et des syénites blanches ont des signatures géochimiques similaires et se caractérisent par des rapports élevés en Nb/Ta typiques de magmas riches en carbonate par immiscibilité. Les syénites rouges ont des caractéristiques de liquides silicatés évolués par différentiation. Les minéraux des carbonatites pauvres en silice ont des rapports Nb/Ta très variables, sub-chondritiques (<10), indiquant une cristallisation à partir de liquides très évolués et la présence de magmas carbonatitiques tardifs. Les apatites, en particuliers, enregistrent divers épisodes magmatiques et également supergènes. Elles présentent dans certaines roches une redistribution et un enrichissement en terres rares variables qui se caractérisent par des exsolutions de britholite dans les carbonatites riches en silice et monazite dans les carbonatites pauvres en silice. Ces exsolutions traduisent des rééquilibrations locales sub-solidus avec des fluides tardi-magmatiques de composition riche en Cl-Th-REE pour l’exsolution de la britholite et S-Ca-P-CO2 pour les inclusions de monazite. L’apatite et le zircon présents dans ces roches alcalines et carbonatites, ont permis de déterminer l’âge de mise en place du complexe magmatique de Ihouahouene à 2100 Ma syn-métamorphique et de confirmer l’âge panafricain de son exhumation. L’étude pétrologique, géochimique et géochronologique des carbonatites et syénites d’Ihouhaouene a permis de mettre en évidence l’origine magmatique de ces roches et de définir les interactions fluides-roches supergènes à l’origine des enrichissements en REE. Les carbonatites et syénites d’Ihouahouene proviennent d’un faible taux de fusion partielle d’un manteau Précambrien riche en CO2. Plusieurs étapes de cristallisation fractionnée et d'immiscibilité ont permis la genèse de ces roches hybrides, piégées le long de grandes zones de cisaillement durant la période de transition Archéen /Eburnéen dans un régime extensif à l’In Ouzzal caractérisé par un environnement granulitique d’ultra-haute-température. / The In Ouzzal Archaean craton represents a succession of intrusive and metamorphic events since Eburnean, and an important marker of geodynamic processes through geological time. The Ihouhaouene area located in the N-W of In Ouzzal terrane in Algeria is unique by the presence of Proterozoic carbonatite intrusions associated with silica-saturated alkaline rocks. These intracontinental carbonatites are among the oldest and exceptional because of their diversity and the presence of unusual rare earth minerals. Carbonatites are pegmatitic or brecciated with fragments of syenite. They are calciocarbonatites with calcite (> 50 vol.%), apatite, clinopyroxene and wollastonite and are associated with red or white syenites in massive outcrops. Syenites are composed of alternating light levels of red alkaline feldspar or wollastonite associated with white feldspar and dark levels of apatite and clinopyroxene. Carbonatites and syenites form a cogenetic suite characterized by an increase in silica and decrease in calcium and CO2 content. The carbonatites have silica content ranging from 5 to 35 wt.%, 28 to 53 wt.% CaO, and 11 to 36 wt.% CO2. Syenites have high K2O (12 wt.%) and low Na2O content (1 wt.%). Carbonatites and syenites have high incompatible element concentrations with high REE content (7000*chondrites and 1000*chondrites, respectively) and high U, Pb, Sr and Th content. Trace elements (eg. Rare Earths, Nb-Ta, Zr-Hf) in magmatic minerals (apatite-pyroxene) of carbonatites and syenites reveal complex magmatic processes at the origin of these rocks involving several stages of fractional crystallization and immiscibility from a CO2-rich melilititic magma. Silica-rich carbonatites and white syenites are characterized by high Nb/Ta, Y/Zr and Rb/Sr ratios, typical of carbonate-rich magmas by immiscibility. The red syenites have characteristics of immiscible differentiated silicate melt. Silica-poor carbonatite minerals have variable subchondritic Nb/Ta (<10) indicating crystallization from highly evolved liquids and the presence of late carbonatitic magmas. Apatites, in particular, record various magmatic and supergene processes. They present, in some rocks, redistribution and enrichment in rare earth elements, which are characterized by exsolutions of britholite in silica-rich carbonatites and monazite-quartz-calcite inclusions in silica-poor carbonatites. These minerals reflect local sub-solidus re-equilibration with late-magmatic fluids rich in Cl-Th-REE for the exsolution of britholite and S-Ca-P-CO2 for monazite inclusions. The apatite and zircon present in these alkaline and carbonatite rocks, allow determination of the syn-metamorphic crystallization age of the Ihouahouene magmatic complex at 2100 Ma and confirm the pan-African age of its exhumation. The petrological, geochemical and geochronological study of Ihouhaouene carbonatites and syenites highlights the magmatic origin of these rocks and constrains the fluid-rock interactions at sub-solidus conditions leading to REE-enrichment. The carbonatites and syenites result from a low partial melting rate of a CO2-rich Precambrian mantle. Several fractional crystallization and immiscibility stages allowed the genesis of these hybrid magmas, trapped along large shear-zones during the Archean/Eburnean transition period in the In Ouzzal terrane, characterized by extensive deformation in ultra-high-temperature granulitic environment.

The diploma thesis is focused on the study of pressure-induced changes in a behavior of RECo2-type compounds. HoCo2 and its substitution of Si instead of Co in Ho(Co1-xSix)2, x = 0,025 were chosen as a representative compounds from this family of materials. Measurements of electric resistivity, heat capacity, magnetization and AC magnetic susceptibility under ambient pressure showed presence of three magnetic transitions for both samples: the change of the easy magnetization direction at TR ~ 16 K, the Curie temperature TC ~ 80 K and the flipping of magnetization of Co magnetic moments into the parallel direction with Ho magnetic moments at Tf ~ 125 K for HoCo2. Under hydrostatic pressures up to 3 GPa, the TR shifts to higher temperatures whereas TC and Tf, both decrease. This probably occurs due to the weakening of the Co magnetism and the strength of exchange interaction between Ho-Co sublattices. The experiment of muon spin rotation demonstrates a pressure influence to the decay of Co magnetic clusters, which occurs at lower temperatures with increasing pressure. It is evident that the hydrostatic pressure directly influences the exchange interaction between Co-Co.

Magnetic properties of RCo2 compounds have been studied since the sec- ond half of the last century. However, there was recently observed new mag- netic state, so-called parimagnetism. The aim of this thesis was to find the real behavior of TmCo2, which exhibits many discrepancies in the published results, by means of preparation of high-quality single-crystals, its characteri- zation around the ordering temperature and to study parimagnetic behavior. Obtained results showed differences between the samples, which should be caused by the instability of Co and Tm magnetism. It might be the reason of discrepancies in the literature. The results however show the same struc- ture of measured curves with two present phase transition. We suggest two possible interpretations: a) magnetic reorientation of Tm magnetic moments below the ordering temperature of the Tm sub-lattice or b) consequent or- dering of the rare-earth sub-lattice followed by ordering of the Co sub-lattice at lower temperature, which seems to be more realistic. We observed pari- magnetic anomalies at 38 K, 80 K, 168 K only in the case of single-crystals containing small amount of impurity phase, which probably affects the for- mation of magnetic clusters. 1

In this work we report on physical properties of Nd2RhIn8 and Nd2IrIn8 rare-earth intermetallic compounds from the RmTnX{2n+3m} compound family. The compounds crystallize in the P4/mmm space group. Both compounds are anti-ferromagnetic with Néel temperatures TN of 10.8 K, 12.5 K respectively and their magnetization curves show characterisic step-like transitions at low temperatures. The measured M(T) and/or M(H) magnetization curves were used to determine magnetic phase diagrams for field along the c-axis. The specific heat of Nd2IrIn8 was analyzed at temperatures T<TN with respect to the dimensionality of the magnetic excitations. In the T>TN region the Schottky specific heat and susceptibility were compared to calculations based on the crystal field scheme in Nd2IrIn8 obtained by ab-initio methods. Powered by TCPDF (www.tcpdf.org)

Masters of Science / Rare-earth (RE) compounds have been an attractive subject, based on the unique electronic structures of the rare-earth elements. In particular, the RETX (RE = rare-earth, T = 3d/4d/5d, transition metals, and X = p – block elements) series is a large family of intermetallic compounds which crystallizes in different crystal structure depending on the constituents. Most of these compounds crystalize in the hexagonal, orthorhombic, and tetragonal crystal structure. On the other hand, the family of compounds RET2X2 adopted the tetragonal crystal structure of the ThCr2Si2 or the CaBe2Be2 with different space groups. Owing to the different crystal structure, these compounds show versatile magnetic and electrical properties such as Kondo effect, complex magnetic behaviour, valence fluctuation, unconventional and conventional superconductivity, heavy fermion behaviour, Fermi and non – Fermi liquid behaviour, metamagnetism, spin – glass, memory effect, crystal electric field (CEF), magnetoresistance and magnetocaloric effect. The history of magnetism reveals that it is closely related to practical applications and magnetic materials from the most vital components in many applications. These are memory devices, permanent magnets, transformer cores, magneto-mechanical devices and magneto-electronic devices. Recent additions to this list include magnetic refrigeration through the studies of magnetocaloric effect as well as spintronics. Magnetic refrigeration (MR) is an emerging technology and shows real potential to enter conventional markets and the principles of MR obeys the magnetocaloric effect (MCE), which is based on the effect caused by a magnetic field on the materials that accept the property of varying the magnetic entropy, as well as its temperature when varying the magnetic field. In this thesis, we report giant magnetocaloric effect and magnetic properties of NdPd2Al2 and RECuGa (RE = Nd, Dy, and Ho) compounds. These investigations were done through measurements of X – ray diffraction (XRD), magnetic susceptibility, ((T)), magnetization, (M(H)), isothermal magnetization, (M(H, T)), heat capacity, (Cp(T)) and electrical resistivity, ((T)). MCE has been studied from the isothermal magnetization and heat capacity measurements.The first chapter of the thesis describes the theoretical background from which the experimental results have been analyzed and interpreted. This is followed by the chapter which presents experimental details and methodology carried out in this thesis. Chapter three presents the results and discussion of the transport, magnetic and magnetocaloric properties of NdPd2Al2 compounds. XRD studies confirm the tetragonal CaBe2Ge2 – type structure with space group P4/nmm (No. 129). The results of (T), (T) and Cp(T) indicate a putative antiferromagnetic (AFM) phase transition at low temperature at, TN = 3 K. On the other hand, (T) data at high temperatures follow the Curie – Weiss relationship giving an effective magnetic moment close to that expected for the trivalent Nd3+ ion. The magnetization results indicate metamagnetic – like transition at a low field that bears a first-order character which corroborates with the Below – Arrott plots. Giant MCE was obtained for the NdPd2Al2 compound similar to those reported for potential magnetic refrigerant materials. Chapter four discusses the magnetic and thermodynamic properties of the series of compounds RECuGa where RE = Nd, Dy, and Ho. XRD studies indicate the orthorhombic CeCu2 – type crystal structure with space group Imma (No. 74) for all three compounds. Magnetic measurements indicate a putative AFM phase transition below 𝑇𝑁 = 7.1, 8.5, and 3.7 K for Nd, Dy, and Ho compounds, respectively. The high-temperature (T) data for all three compounds follow the Curie – Weiss relationship giving an effective magnetic moment close to that expected for the trivalent rare-earth ion. Again, large MCE were obtained for all three compounds similar to those reported for materials that can be used as magnetic refrigerant materials.

The Solid oxide membrane (SOM) electrolysis is an innovative green technology that produces technologically important metals directly from their respective oxides. A yttria-stabilized zirconia (YSZ) tube, closed at one end is employed to separate the molten salt containing dissolved metal oxides from the anode inside the YSZ tube. When the applied electric potential between the cathode in the molten salt and the anode exceeds the dissociation potential of the desired metal oxides, oxygen ions in the molten salt migrate through the YSZ membrane and are oxidized at the anode while the dissolved metal cations in the flux are reduced to the desired metal at the cathode. Compared with existing metal production processes, the SOM process has many advantages such as one unit operation, less energy consumption, lower capital costs and zero carbon emission. Successful implementation of the SOM electrolysis process would provide a way to mitigate the negative environmental impact of the metal industry. Successful demonstration of producing ytterbium (Yb) and silicon (Si) directly from their respective oxides utilizing the SOM electrolysis process is presented in this dissertation. During the SOM electrolysis process, Yb2O3 was reduced to Yb metal on an inert cathode. The melting point of the supporting electrolyte (LiF-YbF3-Yb2O3) was determined by differential thermal analysis (DTA). Static stability testing confirmed that the YSZ tube was stable with the flux at operating temperature. Yb metal deposit on the cathode was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). During the SOM electrolysis process for silicon production, a fluoride based flux based on BaF2, MgF2, and YF3 was engineered to serve as the liquid electrolyte for dissolving silicon dioxide. YSZ tube was used to separate the molten salt from an anode current collector in the liquid silver. Liquid tin was chosen as cathode to dissolve the reduced silicon during SOM electrolysis. After electrolysis, upon cooling, silicon crystals precipitated out from the Si-Sn liquid alloy. The presence of high-purity silicon crystals in the liquid tin cathode was confirmed by SEM/EDS. The fluoride based flux was also optimized to improve YSZ membrane stability for long-term use.

The lower Mount Rogers Formation (LMRF) is described by Rankin (1993) as a sequence of intercalated metabasalts and volcanogenic sediments with minor metarhyolite. We have chosen to examine the sequence of the LMRF units exposed along Elk Garden Ridge, a high shoulder between the summits of Whitetop Mountain and Mount Rogers in the Mount Rogers National Recreation Area in SW Virginia. This sequence represents an uplifted block of LMRF units enclosed by exposures of Whitetop and Wilburn metarhyolites. In the field, progressive lithologic changes can be observed walking up-section along Elk Garden ridge that are indicative of changes in lava compositions and eruptive environments. From the bottom of the section, massive basalts with distinctive 1-2 cm long swallowtail plagioclase phenocrysts grade into vesicular basalts, then into sheet flow basalts, followed by a thick sequence of aphyric and amygdaloidal pillow basalts. Further up section, eruptive products transition into rhyolitic ignimbrites and ash and lapilli tuffs. Boulders of cobble conglomerates near the middle of the sequence and sedimentary layers in between individual sheet flows suggest short periods of relative eruptive quiescence. The only unit broken out in the LMRF by Rankin (1993), Fees Rhyolite, is not observed in the field area, suggesting local differences in topography, eruptive products and eruptive styles across the outcrop area during the deposition of these eruptive products. Petrographically, the rocks reflect the regional greenschist facies metamorphic conditions with chlorite and epidote as primary metamorphic minerals, and unakite-like zones of mineralization. Relict plagioclase and pyroxene phenocrysts persist, as do primary igneous textures and structures. Compositionally, all of the rocks in the Elk Garden Ridge sequence are strongly enriched in alkali metals, with elevated Na2O and K2O contents, and high TiO2 in the basalts. Major and trace element systematics suggest that the chemical signatures of the metabasalts are primary controlled by shallow-level crystallization processes. The LMRF metabasalts share many compositional affinities with later (~570 Ma) rift-related basalts preserved in the Appalachians, suggesting that all of these lavas were formed by melting of a compositionally uniform mantle source, followed by shallow crystallization, despite being separated from one another by large stretches of time and space.

Recycling and recovery of materials and energy from waste is a key factor to mitigate virgin material demands and reduce resource consumption by utilising waste as a resource for new products. However, some critical materials, such as neodymium, are barely recycled because of missing information on amount and disposition of these critical materials within the waste streams. The goal of the study is to quantify recycling potentials from small and electric motors originating from end-of-life vehicles (ELV), electric bicycles and industrial machinery in Germany and the EU with focus on currently lost rare earth elements. Furthermore, innovative approaches to improve recycling of these motors shall be investigated. Therefore, a calculation model to predict current and future waste streams and the incorporated recycling potentials has been developed. The results show an increasing trend of recycling potentials from small and electric motors for all waste streams. The recycling potential of neodymium is estimated at a range of 150 t to 240 t in 2020 in Germany. However, data inaccuracy and the calculation model are likely to cause overestimation of actually available recycling potential and have to be interpreted carefully. In conclusion, disassembly of small and electric motors from ELV and electric bicycles in combination with a subsequent specific recycling process has been identified as promising to improve utilisation of the recycling potentials of rare earth elements from small and electric motors. However, in case recycling quotas are the prior goal of improvement, the application and further optimisation of post shredder technology is more relevant.

<p>Rare earth elements (REEs) are 15 elements in the lanthanide series plus scandium and yttrium. They are essential for clean energy, defense, and other high-tech industries. Production of high-purity REEs, however, is limited to a few countries, posing great supply risks. Separation of crude REE mixtures into individual REEs is the most challenging step because of similar physical and chemical properties of the REEs. Conventional REE purification processes are based on solvent extraction methods, which are inefficient, require thousands of separator units, and produce large amounts of waste. Chromatography methods are inherently more efficient than solvent extraction methods because of orders of magnitude higher interfacial area per unit volume. Low-cost chromatography sorbents, however, do not have sufficient selectivity for REE purification. </p><p>In this dissertation, ligand-assisted displacement (LAD) chromatography was developed for the separation and purification of REEs from complex mixtures. A ligand, which is selective for REEs, can be added in the mobile phase or immobilized in the sorbent to achieve REE separation and purification. Constant-pattern design methods and a general zone splitting strategy were developed for producing high-purity REEs with high yields and high productivities from complex mixtures. The new methods were tested for producing three high-value REEs, called the magnets REEs, which are the key ingredients in permanent magnets, neodymium (Nd), praseodymium (Pr), and dysprosium (Dy), from waste magnets, bastnäsite concentrates, and monazite concentrates. </p><p>A two-zone LAD was designed and tested for recovering high-purity <a>neodymium (Nd), praseodymium (Pr), and dysprosium (Dy) </a>from waste magnets. Three-zone LAD was designed to recover high purity Nd and Pr from bastnäsite and monazite concentrates. High purity REEs (>99.5%) were produced with high yields (>99%) and high productivities (>100 kg REEs/m³/day). </p><p>Compared to conventional solvent extraction methods, the LAD methods are inherently safer and greener, since they do not require flammable organic solvents or toxic extractants and generate much less waste. LAD methods require only a few zones with a small number of columns. They have more than 10 times higher productivity, or less than10 time the footprint, than solvent extraction. The LAD methods are also versatile and adaptable to a wide range of product purity requirement, feedstock composition, or production scale. </p><p>The LAD methods have the potential to transform the conventional solvent extraction methods with low efficiency and high environmental impact into more efficient and environmentally friendly chromatography methods. They can enable the production of the magnet REEs domestically and provide a driving force to change the current linear path of the REEs, from ores to permanent magnets, to landfills, into a more sustainable circular REE economy.</p>

The dissertation is comprised of three manuscripts presenting rare earth element (REE) and neodymium (Nd) isotopic analyses for the groundwaters, surface waters, sediments, and bedrocks of two estuaries along the eastern coast of the United States: Indian River Lagoon, Florida, and Pettaquamscutt Estuary, Rhode Island. This research was performed to understand the behavior of REEs in subterranean estuaries, the REE SGD fluxes, and the Nd isotopic composition of SGD. The selection of these sites offers contrasting geology (carbonate/sand matrix aquifer versus glacial till aquifer sourced from granitoids) and contrasting subterranean estuary structure. In the first site, the flux of REEs to the Indian River Lagoon, FL is comprised of a nearshore source of terrestrial SGD displaying a HREE-enriched fractionation pattern, and LREE- and MREE-enriched sources that originate from the reductive dissolution of Fe (III) oxide/hydroxides in the subterranean estuary and transported by bioirrigation to the overlying lagoon. The εNd(0) value the Indian River Lagoon groundwater is much more radiogenic than those of the surface water and sediments which could be due to the use of fertilizers in adjacent communities. The surface waters Nd isotopic composition appears to be a mixture of weathering of the Anastasia Formation and dissolution of eolian-transported Saharan Dust. In contrast at the second site, phosphate minerals control the surface and groundwaters of the Pettaquamscutt estuary, RI. The weathering of apatite and precipitation of secondary REE phosphate minerals most likely produce the MREE-enriched fractionation patterns of the Pettaquamscutt groundwaters. The further precipitation of the secondary REE phosphates in the surface waters of the Pettaquamscutt yields HREE-enriched fractionation patterns. The radiogenic Nd isotopic ratios of the Pettaquamscutt waters relative to the bedrock further suggest that apatite is the source of REEs. The Nd flux of SGD for both sites is roughly equal to the respective river fluxes; however, the Nd flux of SGD to the Pettaquamscutt is approximately 3 times greater than the SGD flux to the Indian River Lagoon. More research is needed in both environments to evaluate the impact of SGD on the Nd isotopic budget of the oceans. / acase@tulane.edu