Niobium and rare earth elements (REE) are considered as strategic metals in industrialised countries, and are mainly derived from carbonatite-related deposits. Indicator mineral methods for carbonatites using of portable XRF and Quantitative Evaluation of Materials by Scanning Electron Microscopy (QEMSCAN®), shows promise in exploration for Nb and REE. Portable XRF analysis of stream sediments from the Aley, Lonnie, and Wicheeda carbonatites identified 125-250 μm as the ideal size fraction for indicator mineral studies. QEMSCAN® provides (with no additional processing) detection and characterisation of indicator minerals (when found in high concentrations) from carbonatite deposits. Preconcentration by Mozley C800 separator is recommended for sediment samples with low concentrations of indicator minerals. Discrimination diagrams for pyrochlore supergroup and columbite-tantalite series minerals show that minerals from carbonatites occupy the pyrochlore field and extend slightly into the betafite field. Columbite-tantalite series minerals from carbonatites have Mn/(Mn+Fe) atomic ratios ≤0.25 and Ta/(Ta+Nb) ≤0.20. The compositional fields for pyrochlore supergroup and colubmite-tanatlite series minerals from different deposit types partially overlap. / Graduate / 0996 / 0411 / 0372

This thesis focuses on the geochemistry of secondary minerals, mainly calcite but also others such as fluorite and Ca/Al silicates, precipitated throughout the last 1.5 billion years in fractures of crystalline rock, SE Sweden. The work was based on previous reconnaissance studies and has been possible thanks to access to high-quality drill cores and associated mapping data provided by the Swedish Nuclear Fuel and Waste Management Co (SKB). Concentrations of rare earth elements (REEs) and occasionally other metals were determined in a variety of secondary minerals from fractures (mainly open systems) and veins (mainly sealed systems) and in primary minerals from the bedrock. Stable-isotope composition was measured in the secondary minerals. The overall aim was to define the sources, uptake and fractionation of REEs in calcite, and a few other co-genetic minerals, precipitated throughout the geological history under conditions ranging from hydrothermal to low temperatures. Collectively, the findings of the individual studies show that there is no easy and straightforward control of REE abundance and fractionation in calcite and other minerals in fractures and veins in crystalline bedrock settings. For example, the REE features in calcite vary extensively within sub-generations of single vein-precipitating events, on micro scale in transects across individual veins, and unsystematically over the geological history characterised by successively decreasing temperatures of mineral formation. Although the REE content in, and release from, the crystalline bedrock can have an influence on REE distribution in calcite and other minerals, it is of overall minor importance within a given bedrock domain. The main advantage of determining REEs in secondary minerals in fractures and veins in crystalline rock is therefore, as revealed in this work, to assess the character and evolution of the conditions (including features of the paleofluids) during confined mineral-precipitating events.

Biosurfactants are compounds that exhibit surface activity (e.g., reduce surface and interfacial tension) and are derived from natural, biological sources. They are considered green substances due to their natural derivation, biodegradability, and relatively low toxicity. Biosurfactants from multiple classes have been shown to interact with metals, and a review of these interactions is provided. Rhamnolipids produced by Pseudomonas aeruginosa are attracting attention for metal remediation applications. The purpose of this dissertation is to evaluate rhamnolipids' ability to complex rare earth elements, determine the environmental compatibility of novel rhamnolipid diastereomers, and assess the efficacy of rhamnolipid as a collector in ion flotation. Previous research shows rhamnolipids selectively bind elements of environmental concern over common soil and water cations, but there had been no examination of transition metals from the f-block of the periodic table. The f-block elements include the rare earth elements, which are a vital component of nearly every modern technology and subject to supply risk. The interaction between monorhamnolipids and the rare earth elements was investigated by determining conditional stability constants using a resin-based ion exchange method. For the 27 metals examined, the conditional stability constants could be divided into three groups, albeit somewhat subjectively: weakly, moderately, and strongly bound. UO22+, Eu3+, Nd3+, Tb3+, Dy3+, La3+, Cu2+, Al3+, Pb2+, Y3+, Pr3+, and Lu3+are strongly bound with conditional stability constants ranging from 9.82 to 8.20; Cd2+, In3+, Zn2+, Fe3+, Hg2+, and Ca2+ are moderately bound with stability constants ranging from 7.17 to 4.10; and Sr2+, Co2+, Ni2+, UO22+, Cs+, Ba2+, Mn2+, Mg2+, Rb+, and K+ are weakly bound with stability constants ranging from 3.95 to 0.96. The uranyl ion is reported twice due to the ion demonstrating two distinct binding regions. The conditional stability constants were demonstrated to be an effective predictor of metal removal order. The metal parameters of enthalpy of hydration and ionic charge to radius ratio were shown to be determinants of complexation strength. Naturally produced rhamnolipids are a mixture of congeners. Synthetic rhamnolipid synthesis has recently enabled production of four monorhamnolipid diastereomers of a single congener. The biodegradability, acute toxicity (Microtox assay), embryo toxicity (Zebrafish assay), and metal binding capacity of the diastereomers was investigated and compared to natural monorhamnolipid. Biodegradability testing showed all the diastereomers were inherently biodegradable. By the Microtox assay, all of the monorhamnolipids were categorized as slightly toxic by Environmental Protection Agency ecotoxicity categories. Out of 22 parameters tested, the zebrafish toxicity assay showed only diastereomer toxicity for the mortality parameter, except for diastereomer R,R which showed no toxic effects. All the monorhamnolipids interacted with both Cd2+ and Pb2+. Ion flotation is one possible technology for metal recovery and remediation of metal contaminated waters. Ion flotation utilizes charged surfactants to collect and concentrate non-surface active ions at the surface of an aerated solution. Rhamnolipid's suitability as a collector in ion flotation was investigated. A flotation column was designed to test monorhamnolipid efficacy as a collector. Monorhamnolipids form foams and effectively remove Cs+, Cd2+, and La3+ from solution. The efficacy of the flotation process relies on the collector:colligend ratio and valency of the colligend. Flotation of metal solutions showed a removal order of Cd2+>La3+>>Cs+ when the metals were present individually and mixed at equimolar concentrations. When mixed at order of magnitude different concentrations, the flotation order was Cd2+>>Cs+>>La3+. These studies show rhamnolipid has potential to be used for environmentally-compatible metal recovery and metalliferous water remediation, especially for the rare earth elements.

Rare earth elements (REE) are an increasingly important group of metals due to their role in the development of modern technologies. Despite being abundant within the Earth’s crust recoverable ores are uncommon, and their mineralization isn’t as well understood as other abundant ore types. In this work, the mineralization of REE occurring in outcrop samples at Hicks Dome, a cryptoexplosive feature that resides in the Wauboukigou Alnöite Province in southeastern Illinois, was studied to determine the mode of mineralization and the origin of the REE. Xenotime-(Y) was identified with a scanning electron microscope in an intrusive breccia and emplaced during or shortly after the uplift which created the oval doming of the Paleozoic section. Whole rock REE concentrations from ultramafic dikes at Hicks Dome closely match global averages of lamprophyres and carbonatites, with a steep La to Lu slope, and enrichment of light rare earth elements. Hicks Dome has unique characteristics relative to the other intrusions in the Province, such as elevated REE, Th, and doming. These traits indicate that the dome was more closely related to an intrusive body at depth that sourced heat, volatile gases, and a suite of rare elements. Based on these data, the REE mineralization and thorium associated with the siliceous breccia is directly related to the alkaline ultramafic intrusion at Hicks Dome. The volatile rich, hot fluids emanating from the ultramafic magma supplied REE and thorium were mixed with the regional fluids responsible for the IKFD.

More resources are being defined as critical, which can be attributed to the linear economy of ‘take, make and dispose’. An alternative is to implement the circular economy (CE) which could reduce several negative effects, among other things resource depletion. The aim of this thesis is to identify what current sustainability indicators are lacking to assess a resource with the CE concept. This is done by developing CE core indicators, which then are compared with sustainability indicators. The life cycle of rare earth elements (REE) is used as a case study to validate the CE core indicators. To achieve this literature studies and comparative analysis will be performed. Existing definitions and indicators of CE were studied to compile a complete set of core indicators. These compiled CE core indicators were then compared with adapted United Nation (UN) sustainability indicators. The UN indicators were chosen after analysing several different sustainability indicator system and their compatibility with the resource perspective. The main differences between the UN indicators and CE core indicators is that the UN indicators does not include economic aspects such as market diversity and social aspects such as consumption behaviour. However, the UN indicator system includes transportation and governance that could be beneficial to include into the CE concept. The economic viability to perform the CE analysis and non-existing CE indicators for companies and countries were identified as two barriers that could hinder development and efficient use of a CE indicator system. A way to increase the economic viability is to use already generated data for the CE indicator analysis, though the economical aspect has to be studied further. The non-existing CE indicators for companies and countries are counted as a barrier due to the risk of sub-optimisation of one resource. Additionally, the CE indicator results could be misinterpreted to blame a few for the problems of the resource instead of using the results to improve all parts of the life cycle. Further research is also needed to investigate how, or even if, social aspects such as culture and society could be indicated within a CE indicator system. In conclusion, the UN indicator system could be a good baseline to develop a CE indicator system for a resource though further research is needed.

This thesis examines the way in which China's share of the rare earths global industry is constructed as a threat. The central argument of the research is that the US discourse presented a new form of danger through the lens of classical geopolitical thinking, thus, creating a new type of prospective conflict derived from resources that are perceived to be scarce and yet relatively abundant. It argues that the construction of this 'threat' that the US faces is a constant articulation of perceived vulnerabilities in shaping geopolitical identities and reinforcing ideologies through which are carried out by different actors. Rare earths are crucial for modern conditions and their applications include commercial, military and green technology but mining and production are neither economical nor environmentally friendly. The People's Republic of China is the principal exporter of these rare metals, but because of a territorial dispute in the South China Sea in 2010 it has been labelled as a monopoly power. This study seeks to examine the constructed threat that China poses to the US. China, here, is not only constructed to be a resource hungry giant but also a malicious state that would utilise its 'monopoly' status as geopolitical leverage. The thesis will employ discourse analysis and wisdoms of...

Neogene land-mammal localities are very rare in the northeastern U.S.; therefore, the late Miocene/early Pliocene Gray Fossil Site in eastern Tennessee can clarify paleoecological dynamics during a time of dramatic global change. In particular, the identification of ancient forests and past climate regimes will better our understanding of the environmental context of mammalian evolution during the late Cenozoic. Stable isotope analyses of bulk and serial samples of fossil tooth enamel from all ungulates present at the Gray site elucidate paleoecological reconstructions. The herbivorous megafauna include taxa of likely North American and Eurasian ancestry including: the tapir Tapirus polkensis, rhino Teleoceras cf. T. hicksi, camel cf. Megatylopus sp., peccary Tayassuidae, and proboscidean Gomphotheriidae. The tapir, rhino, camel, and peccary yield mean stable carbon isotope (δ13C) tooth enamel values of - 13.0‰, - 13.3‰, - 13.8‰, and - 13.1‰, respectively, suggesting forest-dwelling browsers. This range of δ13C values indicates the presence of a C3 dominated ancient local flora. Because δ13C values decline with increasing canopy density, the ancient temperate forests from the Gray site were moderately dense. The lack of significant C4 plant consumption (i.e., tooth enamel δ13C values < - 9‰) suggests the presence of forests large enough to independently support the continued browsing of sustainable populations of browsers from the Gray site. In contrast, bulk and serial δ13C values ranging from - 0.7‰ to 0.3‰ from a gomphothere tusk support a diet consisting of C4 grasses, suggesting the presence of C4 grasslands within the individuals home range. The rare earth element (REE) analyses of the gomphothere tusk and the teeth of Tapirus and Teleoceras indicates that these individuals shared similar depositional environments; thus, demonstrating the concurrent presence of C3 forests and C4 grasslands in the northeast. Stable carbon and oxygen serial sample variation of the tapir, rhino, peccary, and gomphothere is less than 1.5‰, suggesting minor differences in seasonal temperature and/or precipitation. These data support the possibility of a North American forest refugium in the southern Appalachians during a time typified by more open environments.

Rare earth elements (REEs) are a group of 15 elements in the lanthanide series along with scandium and yttrium. They are often grouped together because of their similar chemical properties. As a result of their increased application in advanced technologies and electronics including electric vehicles, the demand of REEs and other critical elements has increased in recent decades and is expected to significantly grow over the next decade. As the majority of REEs are produced and utilized within the manufacturing industry in China, concerns over future supplies to support national defense technologies and associated manufacturing industries has generated interest in the recovery of REEs from alternate sources such as coal and recycling. A solvent extraction (SX) process and circuit was developed to concentrate REEs from dilute pregnant leach solutions containing low concentrations of REEs and high concentrations of contaminant ions. The separation processes used for concentrating REEs from leachates generated by conventional sources are not directly applicable to the PLS generated from coal-based sources due to their substantially different composition. Parametric effects associated with the SX process were evaluated and optimized using a model test solution produced based on the composition of typical pregnant leach solution (PLS) generated from the leaching of pre-combustion, bituminous coal-based sources. Di-2(ethylhexyl) phosphoric acid (DEHPA) was used as the extractant to selectively transfer the REEs in the PLS from the aqueous phase to the organic phase. The tests performed on the model PLS found that reduction of Fe3+ to Fe2+ prior to introduction to the SX process provided a four-fold improvement in the rejection of iron during the first loading stage in the SX circuit. The performances on the model system confirmed that the SX process was capable of recovering and concentrating the REEs from a dilute PLS source. Subsequently, the process and optimized parametric values were tested on a continuous basis in a pilot-scale facility using PLS generated from coal coarse refuse. The continuous SX system was comprised of a train of 10 conventional mixer settlers having a volume of 10 liters each. A rare earth oxide (REO) concentrate containing 94.5% by weight REO was generated using a two- stage (rougher and cleaner) solvent extraction process followed by oxalic acid precipitation. The laboratory evaluations using the model PLS revealed issues associated with a third phase formation. Tributyl Phosphate (TBP) is commonly used as a phase modifier in the organic phase to improve the phase separation characteristics and prevent the formation of a third phase. The current study found that the addition of TBP affected the equilibrium extraction behavior of REE as well as the contaminant elements., The effect on each metal was found to be different which resulted in a significant impact on the separation efficiency achieved between individual REEs as well as for REEs and the contaminant elements. The effect of TBP was studied using concentrations of 1% and 2% by volume in the organic phase. A Fourier Transform Infrared (FTIR) analysis on the mixture of TBP and DEHPA and experimental data quantifying the change in the extraction equilibrium for each element provided insight into their interaction and an explanation for the change in the extraction behavior of each metal. The characteristic peak of P-O-C from 1033 cm-1 in pure DEHPA to 1049 cm-1 in the 5%DEHPA-1%TBP mixture which indicated that the bond P-O got shorter suggesting that the addition of TBP resulted in the breaking of the dimeric structure of the DEHPA and formation of a TBP-DEHPA associated molecule with hydrogen bonding. The experimental work leading to a novel SX circuit to treat dilute PLS sources was primarily focused on the separation of REEs from contaminant elements to produce a high purity rare earth oxide mix product. The next step in the process was the production of individual REE concentrates. To identify the conditions needed to achieve this objective, a thermodynamic model was developed for the prediction of distribution coefficients associated with each lanthanide using a cation exchange extractant. The model utilized the initial conditions of the system to estimate the lanthanide complexation and the non-idealities in both aqueous and organic phases to calculate the distribution coefficients. The non-ideality associated with the ions in the aqueous phase was estimated using the Bromley activity coefficient model, whereas the non-ideality in the organic phase was computed as the ratio of the activity coefficient of the extractant molecule and the metal extractant molecule in the organic phase which was calculated as a function of the dimeric concentration of the free extractant in the organic phase. To validate the model, distribution coefficients were predicted and experimentally determined for a lanthanum chloride solution using DEHPA as the extractant. The correlation coefficient defining the agreement of the model predictions with the experimental data was 0.996, which is validated the accuracy of the model. As such, the developed model can be used to design solvent extraction processes for the separation of individual metals without having to generate a large amount of experimental data for distribution coefficients under different conditions.

Mining activities, as essential as they are for our economy and our society, bring pollutants such as acid mine drainage (AMD) which contains dissolved metal(loid)s into the environment. There are different technologies currently being practiced to treat AMD, but many of these methods are prohibitive in industry due to high energy, material and labor requirements. This study investigated two emerging technologies to treat AMD with high removal rates of some metals. In addition, as AMD contains strategic metals such as rare earth elements (REEs), hydrometallurgical and biosorptive approaches were used to recover REEs from AMD, hydrometallurgical recovery method was also applied for coal by-products for the method developed. A two-chamber bioelectrochemical system (BES) was used to remove different types of metals from AMD. After 7 days, the pH of the cathode solution increased from 2.5 to 7.3. More than 99% of Al, Fe and Pb were removed, and removal rates of 93%, 91%, 89% and 69% were achieved for Cd, Zn, Mn, and Co, respectively, at the biocathode. Energy-dispersive X-ray spectroscopy (EDS) studies revealed the deposition of the various metals on the cathode surface, and some metals were detected in precipitates from the cathode chamber. During the BES operation, ~30-50 mV of closed circuit voltage was obtained for different conditions. A single-chambered BES study was conducted for the removal of Cd, Ni, and Mn in mine drainage. Compared to a double chamber, a single chamber BES is easier to design and operate. The removal process was studied with activated sludge from a local wastewater treatment plant. The effect of applied voltage, time, and initial concertation of these metals on their removal rate was studied. For Cd initial concentrations of 625 and 165 µg/L, 1.0 V showed the highest removal efficiency, and ~93 and 95% of Cd were removed, respectively. For a Ni initial concentration of 2,440 µg/L, 72% was removed under 1.0 V compared to the control of 77%. However, for a lower initial Ni concentration of 190 µg/L, 1.0 V was better compared than other conditions, and it removed 92% of Ni. For a Mn initial concentration of 1,800 µg/L, 1.0 V had a better result, however, only ~19% of the Mn was removed. For a lower Mn initial concentration of 390 µg/L, 1.0 V was favorable only at 24 h and the removal rate was ~37%. Nanoscale zerovalent iron (nZVI) was used to remove contaminants from AMD. These contaminants include transition metals (Co, Ni, Cu, Mn, and Zn), alkali and alkaline earth metals (Li, Mg, and Ca), metalloid (As), nonmetals (Se and S), and active metal (Al). Purchased nZVI in concentrations of 10-6500 mg/L was used for a reaction duration of up to 480 min. The pH of the AMD increased linearly with increasing concentrations of nZVI, with a maximum of 6.0±0.1 at 6500 mg/L of nZVI. Cu and Al had the highest removal rate among all other elements. With 10 mg/L of nZVI, ~100% of Cu was removed within 120 min. Up to ~98% of Al was removed with 5000 mg/L of nZVI in 480 min. Reuse of the purchased nZVI was studied for the first time for AMD treatment; however, after reuse in the second cycle, the nZVI was no longer effective. Lab-made nZVI by the precipitation method was tested for a longer time of 48 h. Removal rates for different elements did not change after ~8 h (e.g., 480 min), and in general, the lab-made nZVI had better removal efficiency compared to the purchased nZVI, with removal rate of ~28-79% when using 80 mg/L of the lab-made nZVI. Besides Cu, Al, Ni, and Co, successful removal of Mg and Ca, as well as S, Co, Li, As, and Se from AMD was reported for the first time by using nZVI. Different coal ranks were examined for REE concentration from coal ash. Maximum REE content of more than 700 mg/kg was observed for the highest-rank coal (anthracite) sample, and that was used for leaching and recovery studies. Hydrometallurgical processes including leaching, solvent extraction, stripping, and precipitation were performed to recover REEs from coal ash. Nitric acid leaching tests were conducted at 95 ℃ using a 4×2×2 factorial design. The results indicated that the highest rate of light REEs (LREEs) recovery was achieved at the highest molarity of the acid solution, lowest solids content and longest retention time. However, the highest rate of heavy REEs (HREEs) recovery needed only an intermediate level of acid molarity. The highest recovery rates of 90% for LREEs and 94% for HREEs were obtained. Recirculation of the leachate was conducted to prepare the REE-concentrated solution for the solvent extraction. After two stages of leaching, a 33 mg/L of TREE concentration was obtained in the leachate. Solvent extraction (SX) tests conducted using three different extractants, namely, TBP, D2EHPA and Cyanex 572, and their combinations showed that D2EHPA was the best extractant for recovering REEs from the nitric acid leachate solution with an extraction efficiency of 99%. Nitric acid and sulfuric acid and their mixture were used in the stripping tests. The effect of solvent concentration (in the SX process) was also studied in the stripping stage. When 50% solvent concentration was used, a maximum of 58% stripping recovery was obtained. Oxalic acid helped precipitate ~94% of total REEs (TREEs) from the above aqueous solution. Calcination of the product was performed to reach a final product of 0.8% rear earth oxides (REOs). The same process flowsheet was also successfully tested for another coal ash sample. To recover REEs from AMD, two different approaches were carried out including hydrometallurgical technique and more environmentally friendly approach- biosorptive recovery. A complete process flowsheet including either solvent extraction or biosorption, followed by stripping, and precipitation was developed to recover REEs from an unconventional source of AMD for the first time. At the natural pH of 2.5 almost all REEs were extracted from the solution. Metal-loaded organic solution was reused for three cycles, and it was shown that after three cycles, there was no major reduction in the capacity of the extractant. Striping with 6.0 M HNO3 recovered 23.9±0.7, 74.7±2.1, and 53.1±1.4% of LREEs, HREEs, and TREEs from the organic phase accordingly. Using oxalic acid, and for pH of 2.0, 92.9±2.8% of LREEs, 10±1.5% of HREEs, and 56.2±1.8% of TREEs were precipitated. In the biosorptive extraction, >99% of TREEs were extracted from the solution. The REE-bearing bacteria was also stripped with 6.0 M HNO3, 2871.3±114.8 µg/L (45.0±1.8%) LREEs, 3851.0±154.0 µg/L (65.0±2.6%) HREEs, and 6722.0±268.9 µg/L (50.0±2.0%) TREEs were obtained. Both hydrometallurgical and biosorptive methods extracted almost all of the REEs in the AMD, though pH was adjusted to 4.0 for the biosorptive method. After stripping, comparable amounts of TREEs were obtained by both methods.

Three phases of work were performed for this study. First a new form of liberation analysis was created and applied to two coal samples from separate formations. This new method of liberation analysis attempts to remove sources of error found in the traditional form of liberation analysis. This new method is capable of producing results comparable to multiple iterations of the traditional liberation analysis while using only one head sample. The new method relies on the mathematical reconstruction of the data to produce the resulting liberation profile. This allows the user to easily expand the method to include more liberation profiles without greatly increasing the amount of head weight needed. The results of this phase confirm that the products of each liberation profile reconstitute the correct feed ash. The second phase of work focused on the evaluation and concentration of rare earth elements (REEs) present in the refuse streams of coal processing plants found in the eastern United States. Twenty plants were sampled for the fleet study. Samples of these plants' refuse streams were collected and their REE and ash contents were determined. Coal from the Eagle seam, Fire Clay seam, and Fire Clay Rider were collected and tested during the concentration phase. Samples of a waste coal from the Pittsburgh seam and a coal combustion by prodcut were also provided by a third party. The separation methods investigated include multi-gravity separation, electrostatic separation, and selective oil agglomeration. Partition curves from x-ray sorting devices were also applied to REE float-sink data as well. The results of this work show that REEs tend to partition with low ash material when viewing the results on an ash basis. Finally, the third phase of this work involved the application of x-ray sorting technology on different coals. This work showed that the x-ray sorting technology in question is capable of effectively treating prescreened feed with a size range of 2" x 1/4". The work also shows that the x-ray sorting technology also has applications in the power generation field, where it can be used to eliminate elements of environmental concern. / Ph. D.