No description available.

Attenuation of uranium (U) and rare earth elements (REEs) has been observed in stream and wetland sediments, but the geochemical and mineralogical processes involved in sequestering these elements in natural systems are not well understood. The decommissioned Bicroft Uranium Mine near Bancroft, ON uses a modified stream and wetland system to reduce the concentrations of U and other metals in tailings pond effluent to levels below the Provincial Water Quality Objectives. The Bicroft Mine was operated from 1957 to 1963, and processed low-grade (~0.17 wt% U3O8), disseminated U hosted by pegmatite dykes in amphibolite gneiss, forming 2,284,421 tonnes of tailings, deposited into two tailings impoundments. The Bicroft site has since operated as a passively attenuating stream and wetland remediation system for 55 years, demonstrating the potential longevity and viability for long-term sequestration of U and REEs through natural attenuation. To identify U and REE hosts and their stability in the natural environment, colloids, tailings, stream and wetland sediments were analyzed using various methods, including tangential flow filtration (TFF), ICP-ES/MS, scanning electron microscopy, and synchrotron techniques (bulk and µXANES, µXRF, and µXRD). The results show that Fe- and Mn-oxyhydroxides, goethite, and birnessite are the main mineral hosts for U and REEs in both the colloids and sediments. In addition, detrital grains of U- and REE-bearing minerals were found >200 m downstream in colloids and wetland sediments, showing the potential for long range transport of colloids and particulates in the stream system. Seasonal influences on the stability of trace metals in sediments were observed, and may demonstrate the limitations of passively attenuating remediation systems as a viable method for attenuation. Changes in the redox state of the stream system were observed to influence the attenuation of U and REEs, however, changes in the redox state with depth in the wetland sediments were not observed, and showed no direct influence on the attenuation of U and REEs. The results of this study will help to develop better monitoring strategies for U tailings sites and should reduce the impacts of future U mining operations. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2013-05-06 07:44:03.327

Erbium, a rare earth element, has been shown to exhibit characteristic luminescence at 1.54mum due to its internal 4f transition from the first excited state (4pi3/2) to the ground state (4pi5/2). As this emission wavelength falls inside the maximum transmission window of silicon based optical fibers, erbium doped silicon might lead to the opportunity of silicon based optoelectronics. The introduction of erbium in silicon allows excitation through electron-hole recombination and subsequent radiative emission from the rare earth centers. The works reported here describe the structural, electrical and optical properties of crystalline silicon codoped with erbium and boron by ion implantation technique. Four sets of samples, co-implanted with erbium and boron at different Er dose, implantation energy and at different conditions, were prepared. Post-implantation annealing has been performed to recover the implantation damage to an acceptable value and to activate the dopant atoms optically and electrically. PL and EL measurements have been performed in the temperature range between 80K to room temperature. The sample with the lowest erbium concentration and energy gives the best PL and EL results. The observed emission peaks in both PL and EL measurements were at around 1.129mum, ~1.303mum, 1.50mum and 1.597mum at 80K. At higher temperatures, a broader peak at around 1.50mum with long tail towards the both end of wavelength has been observed. The peak at 1.129mum corresponding to the Si band edge emission, the reason for the peaks at around l.303mum has not been identified while the remaining two peaks correspond the Er3+ emission. Virtually no temperature quenching of Er luminescence is observed in some samples rather room temperature intensity is higher than that at 80K. The improvement of the temperature quenching effect on Er luminescence at room temperature has been attained in our results, which is significant improvement in comparison to the result found in the literature. The structural properties were studied by TEM in both cross-sectional and plan view configurations. TEM analyses showed dislocation loops and other defects of random size and distribution from the surface to 600nm below the surface. Er precipitates defects were also seen in the sample doped with Er comparatively at higher dose (1x1015Er/cm2) and energy (1.0 MeV). No detectable room temperature PL and EL signals were observed from the sample implanted at higher doses and energies.

No description available.

The Hoidas Lake Rare Earth Element (REE) Deposit is one of several REE showings which are spatially associated with a regional-scale fault system that cuts through the Rae Province in northern Saskatchewan. The showings occur along the Hoidas-Nisikkatch fault, believed to be a subsidiary of the Black Bay Fault, and consist of multiple REE-enriched veins. Surface outcrops and drilling have delineated a vein system, called the JAK zone, which extends for over 1 km along strike, with the system remaining open both along strike and down dip. The majority of the REE are hosted by fluorapatite and allanite-(Ce), although there are also minor amounts of monazite, bastnaesite and chevkinite which can contain significant concentrations of REE. The veins are dominantly LREE-enriched, specifically La, Ce, and Nd.<p> The mineralization at Hoidas Lake is complex, with the chemical and mineralogical compositions changing with each vein generation. The earliest veins consist of REE-bearing allanite and chevkinite which occur in association with clinopyroxene, titanite, and hyalophane. The allanite-rich veins are followed by veins dominated by red or green apatite, both of which are typically brecciated. Finally, there is a late apatite which crosscuts all previous vein generations. Each of the distinct apatite generations shows discrete chemical variations, particularly in their light rare earth element content, with the total rare earth oxide content ranging from approximately 1.5% in the oldest apatite to as much as 5% in the green apatite.<p> The majority of the apatite and allanite crystals are strongly zoned, reflecting the chemical changes in the mineralizing system through time and, particularly in the earliest vein generations, there are signs of hydrothermal alteration. The early apatite generations typically show the development of monazite inclusions which suggests interaction with hydrothermal fluids, as do the REE-poor rims and bastnaesite alteration observed in the majority of the allanites.<p> The veins are fault controlled and are interpreted to be late magmatic- hydrothermal in origin, with the fluid derived from a magmatic source at depth. Although the exact source of the fluids remains uncertain, the high concentration of REE, as well as Sr and Ba, and a relative depletion in high field strength elements suggests that the mineralization may be related to either an alkali or carbonatitic source.

The Hoidas Lake Rare Earth Element (REE) Deposit is one of several REE showings which are spatially associated with a regional-scale fault system that cuts through the Rae Province in northern Saskatchewan. The showings occur along the Hoidas-Nisikkatch fault, believed to be a subsidiary of the Black Bay Fault, and consist of multiple REE-enriched veins. Surface outcrops and drilling have delineated a vein system, called the JAK zone, which extends for over 1 km along strike, with the system remaining open both along strike and down dip. The majority of the REE are hosted by fluorapatite and allanite-(Ce), although there are also minor amounts of monazite, bastnaesite and chevkinite which can contain significant concentrations of REE. The veins are dominantly LREE-enriched, specifically La, Ce, and Nd.<p> The mineralization at Hoidas Lake is complex, with the chemical and mineralogical compositions changing with each vein generation. The earliest veins consist of REE-bearing allanite and chevkinite which occur in association with clinopyroxene, titanite, and hyalophane. The allanite-rich veins are followed by veins dominated by red or green apatite, both of which are typically brecciated. Finally, there is a late apatite which crosscuts all previous vein generations. Each of the distinct apatite generations shows discrete chemical variations, particularly in their light rare earth element content, with the total rare earth oxide content ranging from approximately 1.5% in the oldest apatite to as much as 5% in the green apatite.<p> The majority of the apatite and allanite crystals are strongly zoned, reflecting the chemical changes in the mineralizing system through time and, particularly in the earliest vein generations, there are signs of hydrothermal alteration. The early apatite generations typically show the development of monazite inclusions which suggests interaction with hydrothermal fluids, as do the REE-poor rims and bastnaesite alteration observed in the majority of the allanites.<p> The veins are fault controlled and are interpreted to be late magmatic- hydrothermal in origin, with the fluid derived from a magmatic source at depth. Although the exact source of the fluids remains uncertain, the high concentration of REE, as well as Sr and Ba, and a relative depletion in high field strength elements suggests that the mineralization may be related to either an alkali or carbonatitic source.

Micrometer-thin rims of hydrothermally altered zircon preserve significant geological information regarding the timing and nature of fluid infiltration. The research presented in this thesis details an investigation of the isotopic and geochemical composition zircon rims from deformed Archean meta-sedimentary rocks proximal to the world class Musselwhite gold deposit. A continuous ablation Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb technique is proposed in conjunction with Secondary Ion Mass Spectrometry (SIMS) U-Pb and LA-ICP-MS REE depth profile methods. These techniques are capable of identifying and analyzing isotopic and chemical modification of zircon rims that are <5 μm thick by ablating directly into the surface of unpolished crystals. The age of analyzed rims is >100 m.y younger than crystal interiors and corresponds to periods of regional magmatism and hydrothermal activity. The measured thickness of rims is variable across single grains and between grain suites suggesting that they do not form as a uniform mantle around the crystal interior. Instead the interacting fluids exploit pre-existing structural weaknesses caused by sedimentary transport and the α-decay of uranium. A novel LA-ICP-MS single element grain 2-dimension mapping technique for unpolished zircon demonstrates preferential element mobility along fractures and in isolated patches. Pressure-temperature experiments were conducted on a zircon reference material under lower greenschist facies conditions to better understand the low temperature incorporation of REEs into the zircon structure. LA-ICP-MS element mapping of unpolished grains reveals that zircon are chemically modified under these conditions, as characterized by an increase in Ce and Y concentration (up to an order of magnitude enrichment) in CePO4-bearing and YPO4-bearing experiments, respectively, when compared with the concentrations of unaltered primary grains. The integration of these micro-analytical techniques on unpolished zircon can provide insight into the timing of low- to moderate-temperature history of supracrustal rocks which would remain otherwise undefined.

No description available.

No description available.

Recent studies funded by the US Department of energy have shown that coal and coal byproducts contain elevated contents of Rare Earth Elements (REEs), making them a potential resource for these critical materials. The approach employed in this research focused on the concentration and extraction of REEs from fine coal refuse derived from various preparation plants in the Appalachian coal basin of the United States. Initial efforts in this research focused on the identification and characterization of REEs in various fine coal refuse streams from nine distinct industrial preparation plants in Appalachia. The average REE content in these materials was determined to be approximately 200 ppm, but the REE content showed a strong correlation to the aluminum content, suggesting that the REEs are closely associated with the clay minerals present in the refuse. Given the relatively low REE concentrations, initial efforts sought to concentrate the REEs through decarbonization and dispersive liberation steps. In these tests, high-shear agitation in the presence of a polyelectrolyte, followed by sedimentation was able to isolate the REE-enriched fine clay particles from siliceous gangue minerals. Following the dispersive liberation step, all samples were found to have an REE content greater than 300 ppm, a benchmark used for many initial exploratory studies. In one case, the REE content was increased by more than 125%. Subsequent extraction tests initially utilized a direct ion-exchange leaching approach with ammonium sulfate as lixiviant. In all cases, the simple ion-exchange leaching process failed to recover significant quantities of rare earth elements, ultimately suggesting that the REEs in fine coal waste may be passivated or bound in a colloidal phase. To access this colloidal phase, several alternative approaches were evaluated, including leaching with alternative ion-exchange lixiviants, reductive leaching, gas-purged leaching, and others. The approach that showed the most promise was strong alkaline pretreatment, followed by ion-exchange leaching with ammonium sulfate at pH 4. A combination of strong alkali and high-temperatures treatment successfully liberated the REEs, converting them to a form amenable to ion-exchange leaching. The highest REE recovery achieved with this method was determined to be 39%. Lastly, bench-scale solvent extraction tests were used to further concentrate REEs in the leach solution and demonstrate that mixed rare earth concentrates can be successfully produced from fine coal refuse. / Master of Science / Since the introduction of personal electronics, rare earth elements (REEs) have become essential raw materials for modern life. They are used in many common household goods such as cell phones, computers, and flat screen TVs. They are also vital components in various industrial, medical, and military applications. Currently, the majority of the world's supply is obtained from China, which has raised concerns on the vulnerability of the supply chain and the potential impacts of supply disruption on clean energy technologies. In light of this risk, the US Department of Energy has classified a number of REEs as critical elements and has subsequently funded research to investigate ways to diversify the supply chain through alternative resources. The approach employed in this research seeks to extract and recover REEs from fine coal refuse. This industrial waste is a byproduct of the coal mining and beneficiation processes. Given the long legacy of coal mining in the Appalachian region, hundreds of millions of tons of fine waste are currently being stored in surface impoundments, and millions of tons of additional fine coal waste is being produced each year from active mining and beneficiation operations. By valorizing this waste material through REE recovery, mining companies will be incentivized to reprocess existing impoundments, ultimately promoting superior economic and environmental outcomes. Despite their name, rare earths are not "rare" from the standpoint of raw abundance; however, their scarcity is derived from the complexity of the extraction and separation processes. In China, the majority of the heavy rare earth elements are produced from ion-exchangeable clays. These clays have REEs weakly attached to the surface, so that they can be readily recovered by washing them with a salt solution that remove the positively charged rare earth ions from surface. The technical approach employed in this project sought to replicate this process for the clay materials found in fine coal refuse. Additional steps were needed to properly concentrate, activate, and extract the REEs; however, the end-to-end processing tests confirmed that mixed rare earth concentrates can be produced from fine coal wastes consisting primarily clay minerals.