Cemented paste backfill (CPB) technology is widely used in the mining industry as an effective means of tailings disposal. CPB is a mixture of tailings, binder, water, and additional admixtures when required. It is prepared in a mixing plant on the ground surface and then transported into the mine cavities through pipelines either by gravity and/or using pumps. To ensure efficiency during transportation and avoid pipe clogging (which can cause unnecessary delays and loss of productivity), fresh CPB must have sufficient flowability. To achieve that, high-range water reducing admixtures, also known as superplasticizers, are usually added to the CPB during mixing. These admixtures are widely used in the construction industry due to their ability to improve flowability without undermining other important engineering properties. However, their influence on the rheology, mechanical strength and environmental performance (reactivity and permeability) of CPB is not fully understood. Thus, experimental studies were conducted to investigate the effects of superplasticizers on the performance properties of cemented paste backfill at different curing temperatures. Yield stress and viscosity of fresh CPB cured for 0, 1, 2, and 4 hours were measured using a vane shear device and a Brookfield Viscometer respectively. Unconfined compressive strength (UCS) of samples cured for 1, 3, 7, and 28 days was determined in accordance with ASTM - C39. Superplasticizer contents were varied as 0%, 0.125%, and 0.25% of the total weight of the CPB. Preparations and curing of the specimens were performed at controlled conditions of 2, 20, and 35 °C to investigate the effect of ambient or curing temperatures. To have a better understanding of the environmental performance of CPB containing superplasticizer, reactivity, and hydraulic conductivity up to 90 days of curing were also investigated. The reactivity was measured using oxygen consumption test while hydraulic conductivity was measured using flexible wall permeability test. Microstructural analyses (thermogravimetric analyses, X-Ray diffraction, and mercury intrusion porosimetry) and monitoring tests (pH, zeta potential, electrical conductivity, and matric suction) were carried out to understand the principles behind the changes of the observed properties. The obtained results show that superplasticizer dosage and temperature variation have significant effects on the rheology, strength development, hydraulic conductivity and reactivity of the CPB. The polycarboxylic ether-based superplasticizer significantly reduces the yield stress and viscosity by creating strong electrostatic repulsion between the solid particles in the CPB and by steric hinderance. The CPB containing the superplasticizer remains fluid for longer period (as compared with the CPB without superplasticizer) due to the retardation of binder hydration. However, high curing temperature induces faster cement hydration, which thickens the fresh CPB. The unconfined compressive strength (UCS) of the CPB containing superplasticizer was observed to be lower in the early age (up to 7 days), which is also attributed to retardation of the binder hydration. At later ages, the superplasticizer improves the mechanical strength as the binder hydration accelerates and the solid particles self-consolidate. Coupled THMC processes in the CPB showed the role played by the changes in electrical conductivity, volumetric water content, matric suction, and temperature on the development of mechanical strength of the CPB containing superplasticizer. Similarly, addition of the superplasticizer in the CPB decreases both the hydraulic conductivity and reactivity of CPB, thus improving its environmental performance. The improvement is largely attributed to enhanced binder hydration and self-consolidation which decrease the porosity of the CPB. Increasing the curing temperature was found to magnify the improvement of the CPB properties by inducing faster binder hydration. The findings from this study will undoubtedly inform the design of CPB structure with better mechanical stability and environmental performance.

The mining industry generates billions of tonnes of waste annually, which is often stored in tailings storage facilities (TSF). This waste is generated from the extraction of ore from surface or underground mines, as well as from metallurgical processing and low-grade stockpiles. TSF can have significant environmental impacts, as they can cause acid mine drainage resulting in the leaching and transport of heavy metals into ground and surface waters. With increasing demand for critical raw material, recent studies have shown that the valorisation of mine waste can be a potential secondary source of critical raw materials. The valorisation of mine waste is possible when the waste is accurately characterised.A novel method that uses multispectral satellite remote sensing and machine learning to estimate the mineral resource in a defunct TSF in the Witwatersrand Basin, South Africa is proposed in this research. Four machine learning models: 1) random forest (RF); 2) adaptive boosting (AB); 3) extra trees (ET); and 4) k-nearest neighbours are developed using supervised machine learning. The models are trained using training data acquired from a TSF with known gold concentration located 3 kilometres from the TSF and deployed on the TSF to predict the gold grades. The results of the machine learning model predictions indicates that machine learning models had high performances for predicting gold grades in the TSF. The AB, RF and ET, models performed best. Their performances were evaluated using the coefficient of determination (R2) value. The R2 values for the machine learning models were 0.95, 0.92, 0.87 and 0.70 for AB, ET, RF and kNN respectively. The mean gold grade predicted was 0.44 g/t by all machine learning models. This was compared to a 2D surficial geostatistical model which estimated 0.35g/t gold in the TSF using ordinary kriging and a 2D vertically averaged geostatistical model with an estimated 0.4 g/t mean gold grade. The short-wave infrared (SWIR) - band 11 at a 20 m spatial resolution had the highest correlation with the reflectance of gold in the TSF. This study demonstrated the value of leveraging multi-spectral remote sensing data and machine learning to perform mineral resource estimation in defunct TSF.

<p>The Athabasca oil sands produce 20% of Canada’s oil, which in turn creates trillions of cubic meters of waste. The Alberta government mandates that oil sands land be reclaimed to its natural state after mining has occurred. Syncrude Canada is currently creating a novel freshwater fen on top of a composite tailings (CT) deposit as a pilot large-scale reclamation project. CT are both microbially and sulfur rich, in addition, the fen could be a potential source of labile organics and sulfate reducing bacteria which could further stimulate sulfur cycling by microorganisms with the potential to stimulate H₂S_(g) generation, a health and safety concern. Therefore, this thesis examines three main research questions regarding this H₂S production within the Sandhill reclamation fen: 1) Is H₂S generation widespread within the porewaters of the CT and sand cap of the developing Sandhill Fen reclamation project? 2)<strong> </strong>Do microbial metabolisms capable of metabolizing Fe and S linked to H₂S generation occur within CT and sand cap of the developing Sandhill Fen? and 3) Will seasonality and ongoing fen construction impact H₂S generation?</p> <p>Field and experimental results herein discuss potential microbial and abiotic metabolisms and pathways that effect sulfur and iron cycling that could affect hydrogen sulfide generation within the composite tailings and developing fen during three seasonal sampling campaigns from June 2010 to July 2011. Results indicate that detectable H₂S_(aq) occurred in the fen porewaters during each sampling campaign, with a trend of increasing H₂S_(aq) concentrations as construction of the fen progressed. Further, enrichment results indicate that microbial sulfur and iron redox reactions are likely affecting the H₂S_(aq) generation. Experimental microcosm results indicate that the CT may contain unstable sulfur species that can contribute to H₂S_(aq) generation and sequestration in the CT as pyrite. Additionally, the evolution of the Sandhill Fen changed the microbial communities that were present <em>in situ</em> as well as shifted dominance of species type in environmental microbial enrichments. The putative function of these bacteria show a shift from autotrophy to increased heterotrophic metabolisms as the fen is being constructed, suggesting the addition of labile organic substrates from the peat and woody debris are both changing the dominant metabolisms and well as increasing microbial diversity to the underlying CT and sand cap of Sandhill Fen. Results of this thesis established widespread microbial Fe and S metabolisms within CT for the first time and indicated that fen reclamation will alter microbial activity with implications for S cycling within CT. Although this thesis covers a short sampling time frame, it is clear that H₂S_(aq) generation is an important factor to consider during large scale CT reclamation. While microorganisms are present and could be impacting Fe and S cycling, the CT materials should be investigated further in regards to their potential for H₂S_(aq) generation. More consideration should be given to inhibiting H₂S_(aq) generation or supporting FeS formation within the reclamation fen.<strong></strong></p> / Master of Science (MSc)

<p>The comprehensive analysis of intact lipids (called lipidomics) can provide information about the presence of microbial communities in an ecosystem and assist in understanding the biogeochemistry in that system. In previous work we had developed a method to determine the profiles of eight phospholipid classes in a soil microorganism by direct-infusion electrospray mass spectroscopy using tandem mass spectrometry. The work done in this study encompasses first the optimization of previous methodology for use with water and sediment samples containing low concentration of phospholipids and large amounts of organic contaminants and secondly the application of this method to the analysis of phospholipids within composite tailings and recycled process water using a triple quadrupole mass spectrometer to determine the intact lipids in the bacterial community. The results are presented illustrating the phosphatidylcholine (PC) and phosphatidylethanolamine (PE) lipids present in composite tailing samples and recycled process water. This thesis begins with the optimization of a direct infusion mass spectrometry method, which allowed the analysis of intact phospholipids within both water and sediment samples. This method allows for high through-put analysis using both the separation afforded by neutral loss and precursor ion scanning modes and a database containing all possible adduct masses to identify and quantify unknown phospholipids. This method was then applied to water and sediment samples obtained from the Syncrude Sandhill Fen composite tailings site. This analysis discovered multiple differences within the water samples attributed to changes both in well temperature and the ongoing reclamation projects resulting in the change in phospholipid profiles. This thesis also outlines the shortcomings of the direct infusion lipidomics method when used for the analysis of complex samples such as composite tailings sediment samples. In summary, this thesis has demonstrated that direct infusion lipidomics can be successfully applied to the analysis of water samples and yield statistically significant differences within the microbial lipidome.</p> / Master of Science (MSc)

This Master’s degree study examined concentration and isotopic trends of dissolved methane, isotopic trends of phospholipid fatty acids (PLFA), and generated 1st order flux calculations to identify and assess biogeochemical cycling of dissolved methane in the first full-scale demonstration of EPL technology in the Alberta Oil Sands Region (AOSR). Base Mine Lake (BML) was commissioned by Syncrude Canada Ltd. in 2012 to facilitate the long-term storage and remediation of Fluid Fine Tailings (FFT) that are generated as a result of bitumen extraction via the Clark Hot Water Extraction (CHWE) processes. The results of this project provide evidence of methane oxidation by type I methanotrophs in BML, reducing dissolved oxygen concentrations in the hypolimnion layer. The FFT layer is identified as a source zone of fermentative methanogenesis, creating saturated conditions of dissolved gases. Dissolved methane is transferred to the water column primarily by advective processes related to FFT consolidation, while diffusion is a significant secondary transfer mechanism. Dissolved methane concentrations decrease significantly across the FFT-water interface where diffusive flux rates decrease by several orders of magnitude. Concentrations decreased linearly through the hypolimnion to trace concentrations by the metalimnion, resulting in a minor enrichment of δ13C of the residual dissolved methane pool. A minor enrichment of δ13C in C14:0, C16:0, and C16:1 PLFA coincided across the same interval, indicating utilization of a less depleted carbon source further away from the FFT-water interface where dissolved methane concentrations were lower. PLFA δ13C signatures were depleted relative to expected values of typical DOC substrates, further supporting the incorporation of a depleted signature by transfer of depleted carbon from dissolved methane. / Thesis / Master of Science (MSc)

No description available.

Mine tailings result from surface mining coastal plain soils and sediments and are redeposited in a slurry form to the mined area. Mine tailing contains a low amount of organic matter, a low pH, and a high P fixation capacity. This research was carried out in the Atlantic Coastal Plain region to determine if mine tailings reclamation could be accomplished by utilization of yard waste compost and wood ash. Yard waste compost was used to increase the organic matter content and wood to increase pH of the mine tailings. Field research was conducted to determine the effect of yard waste compost and wood ash incorporation into mine tailings on (Zea mays L.) and peanut (Arachis hypogaea) yields. Levels of yard waste compost applied to the mine tailings were 1, 2, 4, 6, 8, and 12% by weight, and wood ash was applied twice at a rate of 2.4 t ha⁻¹. Increases in corn and peanut yields on the mine tailings were attributed to increased available water from the application of yard waste compost and to increased pH from the application of wood ash. Successful use of the yard waste compost and wood ashes for reclamation of the mine tailing is shown by the higher peanut yields on the tailings soils than adjacent natural soils. Although the corn grain yields were relatively high (up to 7830 kg ha⁻¹) where yard waste compost and wood ash were applied to the tailings, the overall corn grain yields were higher on the adjacent natural soil. Probable reasons for lower corn grain on the tailings were inadequate available water at times of maximum need and N and/or P deficiencies. Zinc deficiency was induced in corn plants by the high level of P fertilization required to overcome the high P fixation capacity of the mine tailings. The Zn deficiency could be corrected by either foliar or broadcast-disk in application of ZnSO₄. / Master of Science

Rare Earth elements (REEs) are economically important due to their critical applications within multiple industries. This study investigates the Spruce Pine district of North Carolina, testing the economic feasibility of repurposing current mine waste tailings as a rare earth element resource. Spruce Pine is home to several active quartz and feldspar mining operations, with large waste tailing piles generated during the separation process for quartz and feldspar. The mineralogy, composition, and REE budget of the tailings was examined to assess the economic viability of rare earth element extraction. The local geology includes a series of muscovite class pegmatites of Devonian age (390 Ma), intruded into the primarily amphibolite-grade units of the Ashe and Alligator Back formations (Wood, 1996). The waste tailing piles of two on-going quartz mining operations were sampled to evaluate the potential economic feasibility of rare earth element extraction from key accessory phases, including apatite, remaining from the initial separation process. Sample characterization utilized laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray fluorescence (XRF), energy-dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). The results of this investigation support the conclusion that, at the current recovery rate, price of rare earth elements, and cost of refinement, economic recovery of REE from the studied tailings is not viable. However, yttrium and dysprosium offer the highest potential for economic recovery. If some combination of improvements to the extraction process, reduction in refinement cost, or increases in price occur, yttrium and dysprosium are sufficiently abundant that extraction could become economically viable. / Master of Science / Rare Earth elements (REEs) are comprised of the Lanthanide series of elements as well as yttrium and scandium. REEs are economically important due to their critical applications within multiple industries. Current uses include electronics, magnets, lasers, electric motors, optical fibers, nuclear reactor control rods, visual displays, etc. Although the demand for REEs is high, the current sourcing of REEs is quite scarce. This study investigates the Spruce Pine district of North Carolina, testing the economic feasibility of repurposing current mine waste tailings as a rare earth element resource. Spruce Pine is home to several active quartz and feldspar mining operations, with large waste tailing piles generated during the separation process for quartz and feldspar. The mineralogy, composition and REE budget of the tailings was examined to assess the economic viability of rare earth element extraction. The waste tailing piles of two on-going quartz mining operations were sampled to evaluate the potential economic feasibility of rare earth element extraction from key accessory phases, including apatite, remaining from the initial separation process. The results of this investigation support the conclusion that, at the current recovery rate, price of rare earth elements, and cost of refinement, economic recovery of REE from the studied tailings is not viable. However, yttrium and dysprosium offer the highest potential for economic recovery. If some combination of improvements to the extraction process, reduction in cost of refinement, or increase in price were to occur, yttrium and dysprosium are sufficiently abundant that extraction could become economically viable.

[pt] O presente trabalho estudou o comportamento de rejeitos de minério de ferro e de ouro, reforçados com fibras de polipropileno, com o objetivo da aplicabilidade destes compósitos em aterros (pilhas) de rejeitos de mineração. As fibras foram distribuídas de forma aleatória nos rejeitos (matriz) em um teor de 0.5 por cento em relação ao peso seco da matriz. Os rejeitos de minério de ferro e de ouro são classificados como uma areia siltosa e uma argila siltosa, respectivamente. O programa experimental consistiu em ensaios triaxiais convencionais drenados e não drenados (tensões efetivas de confinamento de 50, 100, 200 e 400 kPa) em amostras não reforçados e reforçados com fibras. Ensaios de cisalhamento direto com superfície polida (tensões normais de 25, 50, 100, 200 e 400 kPa) foram realizados para determinar a influência do reforço na fase residual dos compósitos. Ensaios de Microscopia Eletrônica de Varredura (MEV) foram realizados para visualizar a interação fibra-matriz. A análise global dos resultados permitiu mostrar que fibras de polipropileno não modificam o comportamento elastoplástico do rejeito de minério de ferro, porém no rejeito de minério de ouro o comportamento muda para elastoplástico de enrijecimento. A resistência ao cisalhamento incrementou em ambos os rejeitos reforçados, com um ganho mínimo equivalente ao dobro da tensão cisalhante dos rejeitos sem reforço. Com relação à variação volumétrica, o rejeito de minério de ferro apresenta um comportamento dilatante e a adição de fibras incrementa esse comportamento. No rejeito de minério de ouro observa-se que a tendência volumétrica inicial é de contração e depois apresenta uma leve dilatância, porém, com a adição de fibras, o comportamento dilatante é eliminado. Em conclusão, a aplicabilidade das fibras de polipropileno se mostra como alternativa de reforço e melhoria do comportamento geotécnico dos rejeitos de mineração estudados. / [en] The objective of this work is to study the behavior of iron and gold mine tailings reinforced with polypropylene fibers with the objective of the applicability of these composites in landfills (piles) of mine tailings. The fibers were randomly distributed in the mine tailings (matrix), where was used a content of 0.5 percent in relation to the dry weight of the matrix. The iron and gold mine tailings are classified as a silty sand and a silty clay, respectively. The experimental program consisted of conventional drained and undrained triaxial tests (effective confinement stresses of 50, 100, 200 and 400 kPa) in non-reinforced and reinforced samples. Direct shear tests with a polished surface (normal stresses of 25, 50, 100, 200 and 400 kPa) were performed to determine the influence of reinforcement on the residual phase of the composites. Scanning Electron Microscopy (SEM) tests were performed to visualize the fiber-matrix interaction. The global analysis of the results allowed to show that polypropylene fibers do not modify the elastoplastic behavior of the iron mine tailings, but in the gold mine tailings the behavior changes to the strain hardening elastoplastic. Shear strength increased in both reinforced tailings, with a minimum gain equivalent to twice the shear stress of non-reinforced tailings. The strength parameters in the drained, undrained and residual condition of both mine tailings were increased with the addition of fiber. Regarding the volumetric variation, the iron mine tailings exhibits a dilative behavior and the fiber addition increases this behavior. In the gold mine tailings, it is observed that the initial volumetric tendency is contractive and then presents a slight dilatancy, however, with the fiber addition, the dilative behavior is eliminated. In conclusion, the applicability of the polypropylene fibers is showed as an alternative of reinforcement and improvement of the geotechnical behavior of the studied tailings.

Inthe mining industry people remove rock from the ground to obtain a metal ore. Afterprocessing , the uneconomic fraction called tailings is deposited as a slurry in large reservoirs .The processing adds water and chemical agents to the tailings so that the original structure ofthe material therefore changes, which make storage of tailings complicated. If a tailingreservoir c ollapse s , it can damage p roperties and life downstream . In addition, tailings maycontain contaminants that disturb living organism s and contaminated groundwater in the localarea even under normal operation s . Therefore, tracing the contaminants and study ing thestability of the tailing reservoir s are important. The aim of the thesis is to investigate seepage,contaminant transport, tailings compaction and slope stability of the Zhaoli ditch tailingsreservoir (China) during its construction and afterwards. Simulations are performed with thecomputer program GeoStudio . According to the simulations and the conditions , contaminanttransport was highly related with total head. Total head boundary conditi ons have also a largeeffect on slope stability. The area that has most vertical displacement is at the middle of thetailing s reservoir , and the greatest change of vertical displacement is located near the slope,w here the vertical displacement can increa se 0.5 meter over a 1 0 30 meter distance. Theslope stability can be different from case to case, but the original designed tailing reservoirhave a good safety factor, indicating that the slope is not going to collapse easily. / Vi människor villutnyttja malm erna i marken för att skapa ett mer effektiv t industrisamhälleF ör att utvinna så myck et användbara metaller som möjligt tillsätts kemika lier och vattenunder anriknings processen, vilket gör att deponering av de vattenmättade restprodukt erna isandmagasin blir en utmaning med avseende på dammstabilitet och föroreningstransport.Eftersomdet är svårt att ändra på en färdig byggd damm för anrikningssand e n använder dettaexamensarbete av Geostudio för att simulera hur olika parameter påverkaföroreningstransport i dammen, vattenläckage från dammen samt da mmens stabilitet ochsäkerhet. Projektet har simulerat förhållanden i Zhaoli ditch damm i Kina .Simulering i GeoStudio visar att förorening sspridning är stark kopplad till den totalahydrauliska potentialen och materialets hydrauliska konduktivitet. Rand villkoren medavseende på den hydrauliska potentialen utanför dammen även har en stor inverkan pådammvallens stabilitet. De största vertikala sättningar sker i mitten av dammen, och denstörste sättningsgradient finns i dammvallens sluttning, där en vertikal sättning på 0.5 meteröver ett avstånd på 10 3 0 meter beräknas. Deformation är störst på första lagret överberggrunden. Simuleringarna visar att dammvallens sluttning är stab il med en tillräcklig högsäkerhetsfaktor.