Maria Holuszko

As global society moves towards a low-carbon economy, secure access to raw materials becomes the key bottleneck in achieving a green transition. Alternative resources such as coal-based materials have been evaluated for rare earth production in recent years to reduce import dependence and diversify production geographically. This study explores the possibility of using metallurgical coal-based materials from the East Kootenay coalfields in British Columbia as a source for rare earth elements (REEs). First, a characterization study was carried out to understand the target REEs and gangue mineralogy. The results showed that the concentration of REEs in the feed material varied between 230 to 314 mg/kg on an ash basis. When subjected to flotation, most of the REEs (by wt.%) were deported to waste streams such as middlings and tailings due to the inorganic (mineral matter) association of REEs. A mineralogical examination found that one of the rare earth-bearing minerals was monazite and indicated the presence of fine-sized multiple rare earth minerals in the sample. Feedstock materials were studied using different leaching techniques. Results demonstrated that acid baking followed by water leaching (ABWL) was the suitable method for extracting REEs for the samples studied. Acid dosages and bake temperature were found to be the most important process variables affecting REE extraction. The kinetic analysis showed that the process was controlled by interfacial transfer and diffusion through product layer, with an apparent activation energy of approximately 15 kJ/mol. The ability to recover REE ions from the leach solution was examined with a modified fruit peel. Results indicated that the new adsorbent was effective in adsorbing REE ions from the solution following the Langmuir isotherm model, with estimated equilibrium maximum adsorption capacities for Y³⁺, La³⁺, Dy³⁺, Er³⁺ of 34.99, 60.51, 65.08, and 66.79 mg/g, respectively. Further, an economic assessment of two process flowsheets examined for REE extraction showed that plant capacity, REE concentration in the feedstock, and price were key parameters affecting project economics. In addition to REEs, the co-production of other valuable elements from the feedstock has the potential to significantly improve the project’s viability on an industrial scale.

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Electrical and electronic equipment has become an integral part of modern society. With the current technological advances, the life span of this equipment has been shrinking, leading to waste generation and issues related to end-of-life waste disposal. The circular economy model has been proposed to address the growing volume of e-waste. The model encourages reduction and reuse to decrease waste generation and encourages recycling to promote efficient natural resource usage.One of the challenges with promoting the circular economy model for e-waste is the insufficiency or absence of the recycling process for the non-metal fraction. The low value associated with the non-metal fraction increases its probability of being disposed of in landfills. This research explored the possibility of utilizing low-cost physical separation processes common in the mineral processing industry to recycle the non-metal fraction obtained from waste printed circuit board.The study showed that a density-based separation could theoretically be used to separate organic, inorganic, and residual metal streams from the non-metal fraction, thus increasing its reusability. The float-sink test and derived washability curves and washability indices showed that a conceptual three-product gravity separation process could produce an organic fraction with 47% yield at 86% organic content and a reject stream with a 35% yield at 72% fiberglass content. A gravity separation-based flowsheet was proposed for the recycling of non-metal fraction, and the potential applications of the recycled products were identified. Further test work at the pilot level would be required to estimate the process efficiency, related costs and understand the product characteristics for their proper application.This research also provided a simplified approach for determining the loss on ignition that can be used to estimate the separation efficiency. It also showed the applicability of advanced techniques such as inverse gas chromatography and micro-FTIR for analyzing the surface heterogeneity and polymeric identification of non-metal fraction components. Overall, the research used an interdisciplinary approach to provide a potential solution for the non-metal fraction to the recycling industry using tools and processes used in the coal and mineral processing industry.

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Biomass as a renewable energy source can be burnt with coal in a coal-fired plant to reduce the impact of fossil fuel on the environment. The aim of this research is to investigate methods that can improve the co-firing of biomass with coal. Initially, a CFD model was validated by comparison with experimental data reported in the literature. Three mesh sizes were tested to prove that simulation results are mesh independent. The model was then applied to simulate the co-firing process with a 3:2 biomass-to-coal mixing ratio. Unsophisticated modifications of the furnace geometry near the inlet and the swirl angle were introduced to study their effect on co-firing. CFD simulations were extended to study the influence of particle shrinkage on co-firing due to biomass pelletization. Furthermore, fine coal tailings generated from coal processing (CT), raw biomass (RB), and torrefied biomass (TB) were characterized for subsequent CFD investigation on mono-firing and co-firing of the different fuels. Simulation results show that the modified furnace geometry with gradual expansion and a larger swirl angle leads to uniform temperature distribution (1650-1720 K) in the furnace vs. a more variant temperature profile (950-1500 K) for the original furnace geometry. Besides, an increase in the tangential component of gas velocity near the center from 1 m/s to 3 m/s with the modified furnace geometry results in a longer residence time of the particles and further reduction of unburnt fixed carbon by 55% from coal at the exit. With biomass pelletization, simulation outputs show that the compressed particles with particle density 1000 kg/m³ have slower volatilization rate and surface reaction, as well as a shorter residence time. This in turns causes a higher percentage of unburnt fixed carbon at the exit though NO emission is slightly lower. As for the co-firing of biomass with fine coal tailings, results indicate that CT alone, CT+TB, and CT+RB blended fuel are associated with 13%, 10% and 28% unburnt carbon, respectively. It may be concluded that co-firing coal tailings with torrefied biomass is better for co-firing since CT+TB also has the lowest NO emission among the different fuels.

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