Now showing items 1-20 of 173

    • Insights into lunar magma ocean solidification using machine learning and phase equilibria models

      Palin, Richard M.; Bohrson, Wendy A.; Cone, Kim A.; Wendlandt, Richard F.; Bozdag, Ebru; Cannon, Kevin M. (Colorado School of Mines. Arthur Lakes Library, 2023)
      Magma oceans are a common stage in the evolution of terrestrial bodies in the inner solar system and likely elsewhere. Their early behavior—how they convect, cool, and crystallize—helps determine the initial structure of planets and how evolution might proceed. The Earth’s Moon is believed to have experienced an early global magma ocean stage (a direct result of the Moon-forming impact), and attempts to reconcile the Moon’s current structure with how an ancient lunar magma ocean may have initially solidified have provided only general constraints. Previous investigations into lunar magma ocean solidification and consequent compositional stratification have hinged primarily on high pressure-temperature experimental techniques and joint inversion methods that included various assumed bulk silicate Moon compositions. Although the approaches provide valuable insight into a global lunar structure the resolution of experimentally-based approaches is typically. Numerical modeling using phase equilibria calculators provides an opportunity to investigate magma ocean cooling and crystallization more efficiently than experimental approaches and is one of the primary tools used here, forming one of the three projects in this thesis. The other two projects are intertwined—the creation of a lunar basalt database and unsupervised machine learning employing the database—and semi-quantitatively address the distribution of various basalt characteristics on the lunar nearside in an attempt to gain some insight into the subsurface. In general, this thesis uses numerical modelling to investigate aspects of lunar evolution spanning ~4.5 billion years, starting with an ancient molten Moon of Earth-like composition that cools and solidifies along a high melt-fraction path to the Moon’s current [mostly solid] state which records a history of punctuated nearside volcanism and surface-altering impacts. The machine learning work here is novel and the first of its kind in using lunar basalt characteristics to constrain lunar evolution, and only one other phase equilibria calculator model on lunar magma ocean solidification has been published at the time of this writing. The work in this thesis supports the idea of a cumulate mantle overturn, that some degree of mantle displacement, locally or globally, occurred during or at the very end of lunar magma ocean solidification.
    • U-Pb geochronology of detrital, inherited, and igneous zircon from the Triassic Eurydice formation and underlying basement, offshore southeast Nova Scotia, Canada

      Kuiper, Yvette D.; White, Shawna E.; Germain, Rémi; Frieman, Ben M.; Snyder, Mo; Sharp, Jonathan O. (Colorado School of Mines. Arthur Lakes Library, 2023)
      The purpose of this study was to determine the provenance of the Late Triassic syn-rift sedimentary rocks of the Eurydice Formation, part of the Mesozoic–Cenozoic Scotian Basin, and the metasedimentary and plutonic rocks forming its underlying basement, offshore southeast Nova Scotia. During the Paleozoic, the accretion of multiple exotic terranes to Laurentia was followed by the collision with Gondwana and the formation of Pangea. These events led to the formation of the Appalachians. The Meguma terrane of Nova Scotia, Canada, was the last exotic terrane to collide with composite eastern Laurentia. It consists of latest Ediacaran–Devonian metasedimentary and metavolcanic rocks and Devonian–Carboniferous plutonic rocks. The Eurydice Formation is the oldest sedimentary unit in the Scotian Basin, deposited during the Triassic breakup of Pangea. The nature of the underlying basement has been previously inferred from petrographic, geochemical, and geophysical evidence, but provenance study is key to identify the basement. U-Pb LA-ICPMS zircon geochronology was carried out on 22 rock samples collected from historic petroleum exploration wells in offshore Nova Scotia and was supported by optical microscopy and automated mineralogy. Detrital zircon analyses from five late Ediacaran or younger metasedimentary rocks revealed mid-Paleoproterozoic and/or Cryogenian–Ediacaran populations, consistent with signatures observed in exposed portions of the Meguma terrane on land. Three granitoid rock samples yielded Late Devonian to early Carboniferous crystallization ages, consistent with mid-Paleozoic syn- to post-tectonic peraluminous granitic plutons of the Meguma terrane on land. A granodiorite, with a previously reported whole-rock eNd(370Ma) value of ~ -13, yielded a ~573 Ma crystallization age, predating the deposition of the sedimentary and volcanic rocks of the Meguma terrane. This age is consistent with Pan-African high-K calc-alkaline post-collisional plutonism in Northwest Africa, suggesting a potential genetic link. Significant mid-Paleoproterozoic, Ediacaran, and Late Devonian detrital zircon populations in rock samples from the Eurydice Formation suggest local sources from the metasedimentary Meguma Supergroup and from Late Devonian felsic/intermediate plutonic rocks. Notably, an absence of zircon from the rift-related volcanics of the Silurian White Rock Formation of northwest Nova Scotia is observed. These results support the previous interpretation that the Meguma terrane extends to the southeast in offshore Nova Scotia and has a Northwest African origin. Furthermore, zircon grains of the rift-related volcanic rocks of the White Rock Formation are absent southeast of Nova Scotia, suggesting that these rocks are probably not related to the rifting between the Meguma terrane and Gondwana, but between the Meguma terrane and an outboard terrane.
    • Ore mineralogy of the TV and Jeff volcanogenic massive sulfide deposits in northwestern British Columbia, Canada, The

      Monecke, Thomas; Eck, Edgar Cole; DeDecker, John; Pfaff, Katharina; Frieman, Ben M. (Colorado School of Mines. Arthur Lakes Library, 2023)
      The precious metal-rich TV and Jeff volcanogenic massive sulfide deposits are located about ~10 km south of the world-class Eskay Creek deposit in the Iskut River area of northwestern British Colombia, Canada. The deposits are hosted by volcanic successions that form part of the Jurassic Hazelton Group. Drill core samples were collected from multiple holes intersecting the precious metal mineralization to identify the ore minerology, with particular emphasis being placed on the study of the mineralogical sequestration of the precious metals. A combination of reflected light microscopy, scanning electron microscopy, automated mineralogy, electron microprobe analysis, and laser ablation-inductively coupled plasma-mass spectroscopy was used to study the ore mineralogy. Paragenetic relationships in the ores show that three distinct stages can be distinguished ranging from pre-ore sulfide formation to metamorphic recrystallization. Pyrite is the most abundant sulfide phase at the TV and Jeff deposit occurring as framboidal pyrite, As-poor and As-rich subhedral to euhedral grains, porphyroblasts, and recrystallized pyrite grains affected by brittle deformation. The As-rich pyrite displays complex compositional zoning, with many of the zones containing small mineral inclusions. Brittle and ductile deformation are present in pyrite and base metal sulfides. Gold occurs as invisible Au in pyrite but also forms discrete grains of electrum. Silver is common as electrum and is present in a range of Ag-sulfosalts. The observed mineral association and generally low base metal grades at TV and Jeff suggests that precious metal enrichment at these deposits occurred at relatively low temperatures (<200°C). The mineral associations at TV and Jeff are distinct from other Au-rich volcanogenic massive sulfide deposits that are generally polymetallic in nature and have formed from hydrothermal fluids having higher temperatures.
    • Role of Froude supercritical flow in active margin basin-floor fans, The

      Plink-Björklund, Piret; Sapardina, Dessy W.; Miskimins, Jennifer L.; Wood, Lesli J.; Jobe, Zane R. (Colorado School of Mines. Arthur Lakes Library, 2023)
      This dissertation focuses on the active margin basin floor fan and tests the hypothesis that whether Froude supercritical flow and a high degree of channelization are common features in basin floor fans, even in a distal part. The Froude supercritical flow may control the architecture and characteristics of basin-floor fan. To test this hypothesis, two main study regions were chosen in California, which are Cretaceous Point Loma Formation in San Diego and Juncal Formation in Santa Barbara. Cretaceous Point Loma Formation previously interpreted as distal fan deposits, exhibit channelized deposits occur intimately interbedded and laterally related to heterolithic as well as muddy lobe facies. The study reveals that the formation of the submarine fan occurred through channel avulsions rather than bifurcations into distributary channels. Juncal formation demonstrates proximal to distal submarine fan environments. The study shows that supercritical flow structures occur at multiple scales and occur across the whole fan. This work further indicates that supercritical flow in deepwater systems is not limited to high gradients, such as expected in slope systems. The outcrop studies were conducted in conjunction with a review of existing literature to comprehensively document the deposits resulting from supercritical flow in both slope and basin-floor fan environments. The comparative analysis reveals that slope deposits formed under supercritical flow conditions display a greater number of erosional characteristics.
    • Modeling, statistical analyses, and life cycle assessment of anaerobic bioreactors for the treatment of organic wastes and resource recovery

      Munakata Marr, Junko; Figueroa, Linda A.; Callahan, Jennie L.; Cath, Tzahi Y.; Pfluger, Andrew; Ranville, James F.; Vanzin, Gary (Colorado School of Mines. Arthur Lakes Library, 2023)
      Increased application of anaerobic bioreactors can accelerate the transformation of wastewater treatment to energy-efficient resource recovery. These technologies are viable alternatives to traditional aerobic wastewater treatment practices due to their ability to generate methane-rich biogas from the microbial decomposition of organic matter within waste without the need for costly aeration. The biogas can be captured and used in heating or electricity production, potentially eliminating the need for consumption of external fossil fuel-based electricity or natural gas. Barriers to implementation of anaerobic treatment methods may include costs associated with upgrading existing facilities, lack of knowledge of how the treatment processes work or not knowing how adoption may benefit a particular facility. To overcome these barriers and bring anaerobic bioreactors into mainstream use, decision support tools are needed. Computer models and simulations, including life-cycle analysis for environmental impacts, can generate predictions regarding treatment abilities, methane production, carbon dioxide emissions, and costs. These predictions can be used by decision makers to help determine if implementation of anaerobic bioreactors is the best decision for them. To address these research needs, this dissertation creates decision support tools through multiple modeling methods of anaerobic bioreactors, including computer simulation, statistical analyses, waste characterization, and life cycle assessment. The bioreactors examined during the research included three pilot-scale anaerobic baffled reactors (ABRs) treating wastewater in Colorado and full-scale anaerobic co-digestion at a water resource recovery facility in New York. Outcomes of the study of the ABRs include successful modeling of constituent removal and methane generation within 9% through identification and modification of key default parameters within a commonly used wastewater treatment computer simulation program. Additionally, statistical analysis of the wastewater characteristics and performance of the three ABRs identified distinct differences between the systems, but also average constituent removal efficiencies, effluent concentrations, and methane generation. These results can be used to assist with the design and operation of future pilot- or full-scale ABRs operating in colder climates. Finally, three waste streams (wastewater sludge, food, and fats, oils, and grease wastes) were characterized and used to develop a stoichiometric model for methane generation, energy production, and environmental impacts associated with anaerobic co-digestion, with adjustable parameters for use in future research.
    • Pinhole-dependent polycrystalline silicon contacts for high-efficiency Czochralski silicon solar cells

      Stradins, Paul; Agarwal, Sumit; Anderson, Caroline L.; Singh, Meenakshi; Gómez-Gualdrón, Diego A.; Wolden, Colin Andrew (Colorado School of Mines. Arthur Lakes Library, 2023)
      Polycrystalline Si (poly-Si) passivating contact solar cells are emerging as a leading technology in the solar photovoltaic (PV) market. Currently, their deployment is limited to electron-selective contacts on planar surface morphology: this is due to inferior performance of hole-selective poly-Si contacts and poly-Si contacts fabricated on alkaline-textured Si surfaces. Overcoming these limitations could foster broader adoption of poly-Si contact technology. A dielectric interlayer between poly-Si and c-Si is required to mitigate defects at the poly-Si/c-Si interface. Current transport through the dielectric occurs preferentially via direct quantum tunneling, or via discontinuities in the dielectric layer, known as “nanopinholes”. This thesis investigates pinhole-dependent poly-Si passivating contacts and focuses on parameters that control the area density of pinholes. Due to the defective nature of pinholes, tuning pinhole area density is crucial in the optimization of poly-Si contacts. In Chapter 3, the effect of surface morphology on thermal pinhole creation is investigated for poly-Si/SiOx on various textured morphologies. The formation of pinholes in the insulating SiOx layer is induced through thermal processing at temperatures exceeding 1000 ◦C. The findings reveal that textured morphologies exhibit higher susceptibility to pinhole formation compared to planar morphology. Notably, a thermal process capable of selectively creating pinholes at the vertices of inverted pyramid-textured c-Si is identified. In Chapters 4 and 5, a fabrication process is developed for the creation of pinholes at room temperature. This process utilizes galvanic corrosion principles within a wet chemical environment to selectively etch the dielectric interlayer, resulting in the formation of pinholes with widths ranging from ≈10 to 200 nm. Extensive electrical and microscopic investigations reveal that the presence of etch undercut in the dielectric layer leads to the development of electrically resistive pinholes. However, through the implementation of a modified processing sequence that eliminates undercut, conductive pinholes are successfully fabricated. Moreover, the density of pinholes can be finely controlled by adjusting the concentration of the etching solution, offering manipulation within a broad range of approximately 1×10^4 to 5×10^7 cm^(−2). The application of this innovative technique in fabricating hole-selective poly-Si/SiNy/SiOx contacts on both textured and planar c-Si substrates demonstrates excellent hole selectivity, with J_0 <1 fA/cm^2 and ρ_c <30 mΩ·cm^2. Finally, the integration of this process into the fabrication of single-junction single-side textured Czochralski Si solar cells resulted in open circuit voltage of 729.0 mV and a fill factor of 81.9%.
    • Proposed methodology to quantify ESG metrics to better explain the impact on market value: a case study of gold mining, A

      Miller, Hugh B.; Jones, Sarah L.; Dagdelen, Kadri; Spiller, D. Erik; Eggert, Roderick G.; Woodson, Sandra (Colorado School of Mines. Arthur Lakes Library, 2023)
      It is believed by some that environmental, social, and governance (ESG) has become a vital determinant of a mining company’s market value, in addition to the traditional metrics of production, country risk, deposit characteristics, and corporate management. Institutional investment firms, like BlackRock, invest trillions of dollars annually through mutual funds and exchange-traded funds to promote sustainable development by analyzing a company’s positive ESG metrics to support their investment decisions (BlackRock, 2018). Therefore, mining companies must maintain positive ESG performance to access critical institutional funding to continue operations or expand their investment portfolios. Pursuing positive ESG initiatives, like reducing emissions or providing community support, comes at a cost to the firm. Mining companies must determine if the benefit of improved access to funding or any potential increase in market capitalization outweighs the cost of implementing ESG. This thesis aims to determine if six of the largest gold mining companies in the U.S. and Canada have received short- and long-term financial benefits from implementing ESG practices. The short-term impact is evaluated using an event study approach and finds the market has been unresponsive to positive or negative ESG performance information. Regression analysis determined that ESG ratings do not correlate to a firm’s long-term financial performance. ESG ratings are meant to assess the potential financial risks to investors from environmental, social, and internal governance practices that may impact a firm’s reputation or financial profitability. Measuring ESG performance is a qualitative assessment of data gathered through interviews and questionnaires to the firm by an ESG rating analyst or through self-assessment and disclosures using prescribed guidelines. Third-party ESG scores may be subjective as each analyst may change the weight of ESG criteria, and the data used is not always verified or reliable (Lovas, 2021). Unfortunately, the lack of consistency between ESG rating methodologies, metrics, data, and weightings causes confusion and often challenges and frustrates investors (Lovas, 2021). This thesis addresses the lack of universal ESG metrics for the mining industry by recommending new quantitative criteria for evaluating ESG initiatives from a technical perspective. For instance, measuring the environmental risk should consider a firm’s efforts towards biodiversity offsets, energy efficiency, limiting land disturbances, and proper tailings management are all critical risks associated with mining.
    • Understanding the influence of process parameters on the mechanical properties of alumina formed through lithography-based additive manufacturing

      Packard, Corinne E.; Boardman, Sarah V.; Reimanis, Ivar E. (Ivar Edmund); Brennecka, Geoffrey; Brice, Craig Alan, 1975- (Colorado School of Mines. Arthur Lakes Library, 2023)
      Lithography-based ceramic manufacturing (LCM) is a developing additive manufacturing (AM) technology used to fabricate technical ceramics using layer-by-layer forming. However, studies assessing the impacts of processing parameters on the fundamental driving forces for failure of LCM-formed alumina are extremely limited. This thesis provides novel insight into the structure-property-processing relationships in LCM-formed alumina by evaluating the influence of thermal and print-based process parameters on the density, flexural strength, and flaw populations. This thesis begins with the development of a multi-step thermal treatment to fully densify LCM-formed alumina. Attaining fully dense specimens is a prerequisite to flexural strength characterization as density and strength are directly correlated. The effect of thermal treatment is assessed via flexural strength and density measurements as well as the resultant grain size and grain morphology. The thermal processing study identified a set of conditions in which specimens are fully dense and also have a grain size, characteristic strength, and Weibull modulus comparable to conventionally-processed alumina from a round robin study. Next, this work examines the impact of multiple LCM print parameters (including orientation, layer height, and energy) on the flexural strength, Weibull modulus, and flaw population of LCM-formed alumina. The findings reveal orientation and layer height print parameters do have a meaningful impact on the characteristic strengths, Weibull moduli, and flaw populations. Fractography reveals different print parameters lead to different strength-limiting defects, and all strength-limiting defects originate from the printing process. Finally, flaw populations are evaluated in a complex specimen geometry, finding the same type of print-based flaws responsible for failure. This work determines characteristic strengths of AM alumina are near or above conventionally processed alumina. Additionally, under many print conditions Weibull moduli are near or above conventionally processed alumina but underperforms conventional alumina in the vertical orientation. Delamination defects are the most detrimental defect to Weibull moduli in vertically oriented specimens. Print-based flaws are evident in all configurations but not all flaws are significantly detrimental to performance when compared with conventional material. The analysis shown in this thesis provides a framework which enables future studies of other LCM-formed technical ceramics.
    • Offshore El Salvador: the first interpretation of a unique 2-D seismic dataset and implications for a working petroleum system in a forearc basin setting

      Trudgill, Bruce, 1964-; Branda, Alex N.; Burton, Bradford; Sonnenberg, Stephen A. (Colorado School of Mines. Arthur Lakes Library, 2023)
      The unexplored Acajutla Basin is located within a forearc setting along the Pacific coast of El Salvador. It is a part of a larger system of forearc basins that lie between the coast of Central America and the Middle America Trench, running parallel to the Pacific coastline from central Mexico to Costa Rica. Interpretation of 3,700 kms of 2D seismic data reveal the presence of a deep depositional basin bounded on the northeast by the Central American Volcanic Arc and on the southwest by a basement ridge that forms a prospective anticlinal closure approximately 100 km offshore. The basin contains in excess of 9,000 m of mostly Mesozoic through Cenozoic sediments. In the Acajutla basin, seven sequence boundaries have been identified that are continuous and display high to moderate reflective amplitudes, encompassing Late Cretaceous through Pleistocene intervals. Structure contour and isochron maps are generated on mapped sequence boundaries correlated from adjacent regional well-tied seismic surveys offshore Nicaragua and Guatemala. Significant truncation and structural dip reversals have been mapped across the research area below the shelf edge at the outer arc high. Little drilling has taken place in the forearc basins of Central America; none whatsoever offshore El Salvador. Lack of success can be attributed to the complex tectonic evolution of forearc basins as it pertains to deposition of suitable source rocks, maturity, timing, and migration of hydrocarbons. The Corvina-2 well offshore Nicaragua, and the Esso Petrel-1 and Madre Vieja-1 offshore Guatemala aid in constraining lithological data in the region. Maturity data from regional studies indicate that source rock intervals have reached a stage of thermal maturity below a depth of 3,000m. Basin modeling indicates maturity across the forearc basins within varying geological units and depths. Research will focus on defining chronostratigraphic boundaries, thermal maturity models, and the overall tectonic and depositional evolution of the Acajutla Basin.
    • Failure conditions and triggers of the Achoma landslide, central Andes region, Arequipa Peru

      Santi, Paul M. (Paul Michael), 1964-; Alarcon, Oscar; Walton, Gabriel; Pederson, Christopher (Colorado School of Mines. Arthur Lakes Library, 2023)
      The Colca Valley has historically been subject to a variety of geological hazards such as landslides, rock falls, and debris flows. On June 18, 2020, a rotational landslide occurred near the community of Achoma in the Colca Valley. The event destroyed agricultural land, impacting the finances of many families, and the displaced material crossed the Colca River and created a dam that increased the risk of flooding for the towns upstream. To estimate the critical groundwater conditions that caused the Achoma landslide, limit equilibrium and finite element analyses were completed. Also, forward modeling was completed to analyze the hazard posed by further movement of the scarp. The research relied on two-dimensional models that required several kinds of information to provide valid results. At the Achoma site, the information on the strength of in situ soil and rock materials and the depth and distribution of groundwater is extremely limited and the access to the zone is restricted and dangerous. Therefore, remote sensing data was used to inform these parameters, accompanied by probabilistic analysis. The use of satellite images, drone images, and three-dimensional models was also vital to complete the research. The slope stability was dependent on lacustrine sediments composed of clayey silts interbedded with sandstones and conglomerates of the Colca formation. The trigger of the landslide was a combination of natural and anthropogenic factors which produced changes in the groundwater levels. The principal causes identified are rainfall, extensive irrigation activity on the landslide area, and potential leakage from an irrigation project conformed by a canal and tunnel uphill from the landslide. Considering the results, we observed differences in the influence of the different triggering mechanisms. The impact of the rainfall was low to moderate because almost no rain occurred two months before the landslide. The agricultural activity in the area has a moderate influence because the irrigation could result in excess water percolation to the perched water table. And finally, the effect of the Majes-Siguas canal and tunnel observed was moderate-high. Models results show that the leakage from the tunnel is more likely than leakage from the canal.
    • Elucidating protein-protein interactions that regulate the structure of bacterial protein assemblies using multiscale modeling methods

      Pak, Alexander J.; Halingstad, Ethan Vebjorn; Boyle, Nanette R.; Beeler, Suzannah M. (Colorado School of Mines. Arthur Lakes Library, 2023)
      Self-assembling protein structures have a wide range of functions in many bacterial species. In the spore-forming bacterial pathogen Bacillus anthracis, a protective paracrystalline monolayer composed of the surface layer protein Sap is an important virulence factor that enables the spread of the disease anthrax. In many bacterial species such as Haliangium ochraceum, self-assembling bacterial microcompartments compartmentalize enzymes that aid in the energy production and metabolism of the organism. The understanding of the mechanisms of assembly of both complexes has important implications for therapeutic and metabolic engineering. In vivo, nanobody-mediated disruption of the B. anthracis surface layer attenuated bacterial growth and prevented lethality. Revealing the mechanism of self-assembly may provide insight into the design of protein therapeutics with increased affinity and effectiveness. Metabolic engineers are also interested in repurposing bacterial microcompartments for non-native functions. Identifying molecular driving forces and assembly conditions that direct the morphology and cargo of bacterial microcompartment shells can guide the engineering of novel microcompartment shells to encapsulate non-endogenous enzymes and expand the range of metabolic activity. Here, I propose the use of multiscale modelling to highlight the effect of protein flexibility on the exposure of key protein-protein interfaces in these self-assembling proteins. By generating and validating an atomistic model of the Sap protein lattice, I aim to identify the interactions responsible for lattice assembly to guide future nanobody design. I also provide a framework for the coarse-grained modeling of a hexameric H. ochraceum microcompartment subunit. The ability of this model to accurately capture the morphologies observed in in vivo and in vitro experiments will enable the in silico modeling of other microcompartment subunits that can be used collectively to explore the morphological landscape of microcompartment assemblies, further leading to the engineering of microcompartments that expand the range of microbial metabolism.
    • Gallium extraction from zinc plant residues by chlorination roasting

      Taylor, Patrick R.; James, Stephen E.; Iriarte Aguirre, Santiago; Spiller, D. Erik; Anderson, Corby G. (Colorado School of Mines. Arthur Lakes Library, 2023)
      The demand for semiconductors and the renewable energy transition has increased the demand for gallium, indium, and germanium. The US Department of Energy considers these elements critical due to their scarcity, lack of substitutes, and import dependence. Some sphalerite concentrates contain trace amounts of Ga, In, and Ge. During the processing of sphalerite, Ga, In, and Ge are concentrated during leaching. However, Ga, In, and Ge co-precipitate with the iron sulfates and other impurities during the iron removal stage. These zinc processing residues are promising sources for Ga, In, and Ge; however, there are technological limitations to recovering these elements. Chlorine metallurgy has been studied to recover metals from complex ores, treat waste, or recover critical elements in waste streams. It has been evaluated for the recovery of valuable material from sulfides, oxides, and silicate ores. Moreover, chlorine metallurgy offers several advantages, such as opening ores, selectivity, regeneration of the chlorinating agents, and process versatility. Thus, the following study presents chlorination roasting as a possible method to recover gallium from domestic zinc processing residues. The study consists of chlorination roasting of two different zinc processing residues for the recovery of gallium. The study discusses the effects of temperature and chlorine gas concentration on the extraction via chloride fuming of Ga, Fe, Pb, and Zn. Gallium extractions of 50%, 60 %, and 80 % were achieved from zinc processing residues. Moreover, zinc extractions of 60% and 80% were also achieved. Selective volatilization of gallium, germanium, and indium chlorides was studied and found to be a promising approach for refining. A preliminary flow sheet for gallium recovery from zinc processing residues via chlorination roasting was identified and evaluated. The preliminary techno-economic analysis found that the gallium grade in the zinc processing residues is crucial for an economically feasible process. It was determined that chlorination roasting is a technologically feasible process for the recovery of gallium.
    • Integrating full-bore formation micro-imager (FMI) data for Niobrara reservoir characterization, Postle area, Wattenberg field, Colorado, USA

      Sonnenberg, Stephen A.; Hillman, Eric A.; French, Marsha; Jin, Ge (Colorado School of Mines. Arthur Lakes Library, 2023)
      The Ancestral Rocky Mountain orogeny formed the paleo-Denver Basin approximately 300 million years ago and was followed by the Laramide orogeny that created the present-day Denver Basin. The Western Interior Basin existed between the orogenic events during the Cretaceous. Deposition of the Niobrara Formation in the Western Interior occurred when interactions between the warm paleo-Gulf of Mexico waters flowed northward and the cooler currents from the Artic flowed southward. The Niobrara Formation lithologies represent periods of fluctuating sea-level conditions resulting in the deposition of chalks, marls, sandstones, and shale cycles. The Wattenberg Field is in the Denver-Julesburg (DJ) Basin in northeast Colorado, north of Denver across the synclinal axis of the Denver Basin and covers approximately 81 townships. The Wattenberg Field development and production started in 1970, with the majority of production coming from vertical drilling of the Lower Cretaceous J Sandstone. The Upper Cretaceous Niobrara and Codell Formations became important producers in the 1980s. In addition, production in the Wattenberg Field is found in the Dakota, D Sandstone, Greenhorn, Terry, and Hygiene Sandstones. Continuous hydrocarbon accumulations are common throughout the Field. The Wattenberg gas Field is one of the largest natural gas fields in the United States, with resource estimates from the Niobrara being approximately 3-4 billion barrels equivalent (BBOE). This study will include a detailed fracture characterization of the Niobrara Formation in the Postle area of the Wattenberg Field, which will help characterize both natural and induced fractures within the Niobrara Formation. Formation micro-resistivity image (FMI) log interpretation indicates a strong orientation preference created through hydraulic stimulation and suggests that the present-day stress orientation is not a result of reorientation due to production and stimulations. Interpretation of the image log data can establish the spatial geometry of the natural and induced fractures within the wells and will help characterize the fractures that help produce hydrocarbons by hydraulic stimulation.
    • Effect of defects and a build pause on fatigue life of additively manufactured 316L stainless steel

      Gockel, Joy; Richardsen, Simon Douglas; Findley, Kip Owen; Brice, Craig Alan, 1975- (Colorado School of Mines. Arthur Lakes Library, 2023)
      Build pauses can occur during metal additive manufacturing (AM) with laser beam powder bed fusion (PBF-LB) for a variety of reasons such as power outage, insufficient gas flow, or sensor failure. It is economically desirable to continue a build after the issue is resolved. The effect on part quality, namely microstructure, surface roughness, geometric features, and the impact on the fatigue performance is not well understood. This study considers parts fabricated with a 2-hour build pause in the center of the gauge section. Comparisons of the dimensions, as-printed surface features, microstructure, and fatigue performance are determined. Geometric deviation from part shift during the build pause is significant, however other flaws inherent to AM can also dominate failure depending on severity. A stress intensity factor approach is utilized to determine the influence that the geometric variation and the individual flaws had on the fatigue life. A model is developed to predict and determine part performance after a build pause. Understanding the effect of mechanical changes and geometric shifts from a build pause can help reduce scrap from unintended build interruptions.
    • Full-waveform inversion of time-lapse seismic data using physics-based and data-driven techniques

      TSvankin, I. D.; Liu, Yanhua; Tura, Ali; Shragge, Jeffrey; Ganesh, Mahadevan; Wakin, Michael B.; Lin, Youzuo (Colorado School of Mines. Arthur Lakes Library, 2023)
      Time-lapse (4D) full-waveform inversion (FWI) is an advanced seismic technique that can enable accurate estimation of changes in the subsurface properties, such as fluid saturation or reservoir depletion, by utilizing amplitude and phase information in seismic data. However, most existing 4D FWI research is limited to isotropic and, often, acoustic media, which hinders its application to realistic subsurface models. In this thesis, I develop an efficient 4D FWI algorithm for elastic transversely isotropic media with a vertical (VTI) and tilted (TTI) symmetry axis. In addition, I employ a ``source-independent" technique to mitigate the influence of errors in the source wavelet on the results of time-lapse FWI. Furthermore, the thesis presents machine-learning techniques with uncertainty quantification to efficiently perform real-time monitoring with high spatial resolution. First, I extend the methodology of time-lapse FWI to elastic VTI media. The algorithm is tested on multicomponent and pressure data using three common time-lapse strategies: the parallel-difference (PD), sequential-difference (SD), and double-difference (DD) techniques. The multiscale approach is adopted to mitigate cycle-skipping. Synthetic tests show that the proposed methodology can reconstruct localized time-lapse parameter variations with sufficient spatial resolution. The DD strategy produces the most accurate results for clean and repeatable time-lapse data because it directly inverts the data difference for the parameter changes. VTI algorithms become inadequate in the presence of an even moderate symmetry-axis tilt. Therefore, next the time-lapse FWI methodology is extended to 2D tilted TI models. The symmetry-axis tilt is incorporated into the modeling code and computation of the inversion gradients by rotating the stiffness tensor using the Bond transformation. Comparison between the TTI and VTI algorithms confirms that incorporating tilt improves the accuracy of the inverted medium parameters, especially when the reservoir is located in a dipping layer. In addition, I discuss the influence of several common nonrepeatability issues on the time-lapse inversion results for TTI media. FWI requires an accurate estimate of the source wavelet, which is both time consuming and often challenging for field-data applications. The so-called ``source-independent'' (SI) technique is designed to reduce the influence of the employed source wavelet on the FWI results. Therefore, I incorporate the convolution-based SI technique into the developed 4D FWI algorithm for both VTI and TTI models. The SI method substantially reduces the dependence of the estimated parameters on the accuracy of the source wavelet and guides the inversion toward the global minimum of the objective function even for a strongly distorted wavelet and noisy data. Then the developed 4D FWI methodology that incorporates the SI technique is applied to the time-lapse streamer data from Pyrenees oil/gas field in offshore Australia. Despite the pronounced nonrepeatability in the baseline and monitor surveys, the developed algorithm successfully reconstructs the velocity variations in the reservoir caused by hydrocarbon production. The case study demonstrates the importance of accounting for anisotropy and elasticity in time-lapse inversion and confirms the effectiveness of the SI technique when the source wavelet is distorted. To alleviate the ill-posedness and high computational cost of FWI, I propose an efficient ``hybrid'' time-lapse workflow that combines physics-based FWI and data-driven machine-learning (ML) inversion. The scarcity of the available training data is addressed by developing a new data-generation technique that operates with physics constraints. The proposed approach is validated on a synthetic CO2-sequestration model based on the Kimberlina reservoir in California. A large volume of high-quality and physically realistic training data, generated by the algorithm, proves to be critically and efficiently important in accurately characterizing the CO2 movement in the reservoir. The deterministic neural network described above, however, yields only one prediction for a certain input, which may not properly reflect the distribution of the entire testing data, especially when those data are out-of-distribution. To estimate the entire distribution of the target variable along with the prediction accuracy, I incorporate the Simultaneous Quantile Regression method into the developed convolutional neural network. Testing on the Kimberlina data demonstrates the accuracy of the obtained uncertainty estimates, even if the testing data are distorted due to problems in the field-data acquisition. In addition, the proposed novel data-augmentation method can further improve the spatial resolution of the determined time-lapse velocity field and reduce the prediction error.
    • Open-pit mine planning with operational constraints

      Dagdelen, Kadri; Johnson, Thys B.; Deutsch, Matthew Vernon; Newman, Alexandra M.; Mehta, Dinesh P.; Kaunda, Rennie (Colorado School of Mines. Arthur Lakes Library, 2023)
      Open-pit mines must be designed to develop the Earth’s natural resources in the most responsible, sustainable, and economic way. Traditional mine planning optimization methods do not consider operational constraints; such as minimum mining width or minimum pushback width constraints, and often do not generate realistic, actionable designs. This dissertation develops techniques to incorporate operational constraints into open-pit mine planning which allows for engineers to more accurately convert mineral resources into mineral reserves and better evaluate the economic viability of open-pit mining projects. A major practical challenge is that the resulting mathematical models are very large, with potentially hundreds of millions of variables and constraints. Addressing this challenge and delivering tools which are usable on real-world 3D datasets requires a theoretically motivated and computationally grounded approach. The first contribution of this dissertation is an efficient implementation of the pseudoflow algorithm for the well known ultimate pit problem. Modest theoretical improvements and practical computational improvements combine to create a fast and efficient open source ultimate pit optimizer, called “MineFlow,” which is more performant than all evaluated commercial alternatives. A model with sixteen million blocks which takes over three minutes to solve with a commercial ultimate pit optimizer is solved in nine seconds with this implementation. The second contribution is a formulation and methodology for the ultimate pit problem with minimum mining width constraints. These operational constraints restrict the shape of the ultimate pit in order to provide suitably large operating areas which can accommodate the large machinery used in open-pit mining. This problem is shown to be NP-complete and several optimization approaches are developed in order to compute high quality results for large block models in a reasonable amount of time. The two most effective approaches use Lagrangian relaxation and the Bienstock-Zuckerberg algorithm which are modified for this problem. Moreover, the formulation is extended to open pit direct block scheduling problems with operational constraints and solved using a newly developed method based on the Bienstock-Zuckerberg algorithm. This approach is applicable to large, realistic, open-pit planning problems that span multiple time periods and multiple possible destinations for each block.
    • Instigating buoyancy driven convection to improve membrane distillation performance

      Tilton, Nils; Mabry, Miles; Cath, Tzahi Y.; DeCaluwe, Steven C. (Colorado School of Mines. Arthur Lakes Library, 2023)
      Membrane distillation is a thermally driven desalination process that is capable of treating complicated wastewaters with high concentrations of dissolved solids. However, temperature polarization and concentration polarization reduce its distillate production and impede its industrial adoption. Surprisingly, no prior work has considered that temperature and concentration polarization both increase the feed density near the membrane. In this exploratory study, we explore whether these differences in local feed density can instigate buoyancy driven convection in the feed flow and mitigate polarization. We also explore whether we can strengthen this convection by actively heating the feed channel in a direct contact membrane distillation (DCMD) system. For that purpose, we develop several actively heated prototypes and perform a series of experiments to explore how active heating affects distillate production. The prototypes are tested in multiple orientations to determine if buoyancy driven convection is truly taking place. The tests are also performed at multiple feed flowrates and feed concentrations to explore how temperature and concentration polarization affect the development of buoyancy driven convection. Overall, our experiments suggest that, with the cell oriented properly, buoyancy driven convection can be harnessed to significantly improve distillate production. For all flowrates tested, we observed a linear increase in distillate flux with increasing wall heating. The impact of wall heating also increases as the flowrate decreases.
    • RNN seismic velocity model building: improving generalization using a frequency-stepping approach and hybrid training data

      Shragge, Jeffrey; Alzahrani, Hani Ataiq; Sava, Paul C.; Nychka, Douglas; Li, Yaoguo; Jobe, Zane R. (Colorado School of Mines. Arthur Lakes Library, 2023)
      Data-driven artificial neural networks (ANNs) demonstrably offer a number of advantages over conventional deterministic methods in a wide range of geophysical problems. For seismic velocity model building, judiciously trained ANNs lead to the possibility of estimating high-resolution subsurface velocity models at a low computational cost. However, a significant challenge of ANNs is training generalization, which is the ability of an ANN to apply the learning from the training process to evaluate test data not previously encountered during the training process. In the context of velocity model building, this means learning the relationship between velocity models and the corresponding seismic data from a set of training data, and then using acquired seismic data to accurately estimate unknown velocity models. While generalizing to testing models with structures similar to those found in the training data has become a manageable task as evidenced in the recent literature, extending generalization to more realistic scenarios where testing models may exhibit drastically different velocity structures and/or distributions than those in the training data set remains an important and ongoing research challenge. To address this issue, this thesis develops and present the applications of a multi-scale approach inspired by physics-based full-waveform inversion that uses recurrent neural networks to invert frequency-domain seismic data using a frequency-stepping scheme. The input data consist of a sequence of seismic frequency slices that are fed to the network progressively from the lowest available to the highest usable in the data. I combine this approach with a hybrid training approach that merges background velocity gradient models with purely geometrical and geologically realistic model structures. This combination increases the range of spatial wavenumbers as wells as the variability of geological structures present in the training data. I demonstrate the potential for improved generalization by comparing the model estimates results from two trained networks: one using a hybrid set of models, the other with only geological models. I test the two networks using subsets of the community BP2004 benchmark model with complex salt structures fully absent from the models used in the training process. Qualitative analysis shows that models recovered using hybrid training data are significantly more accurate than those recovered using geological training data alone, with arbitrarily shaped salt bodies being accurately delineated by the trained hybrid network. In addition, I demonstrate through a quantitative SSIM metric analysis that the developed RNN extends the range of structures recoverable by the trained ANN. The developed approach illustrates the potential of neural networks to learn the seismic velocity model building problem at a general level from a representative set of training models, and opens the way for more research into improving the design of non-geological training data to further improve network generalization.
    • Comparison of respirable dust characteristics from full-scale cutting tests with conical picks at three stages of wear

      Rostami, Jamal; Slouka, Syd; Brune, Jürgen F.; Miller, Hugh B.; Handorean, Alina; Tsai, Candace (Colorado School of Mines. Arthur Lakes Library, 2023)
      In environments where mechanical excavation systems break rock, airborne rock dust is generated and could pose respiratory health threats to workers. These environments include mining and civil applications with roadheaders, continuous miners, or similar machines used in underground operations. Therefore, this study aims to compare the characteristics of rock dust generated by conical pick cutters at various wear conditions. With supplemental experiments, the results can aid future evaluations of proper bit management, dust suppression, and control systems. The work conducted under this study included full-scale laboratory cutting of concrete, limestone, and sandstone samples. Three symmetrically worn conical picks cut each sample at a new, moderately worn, and fully worn stage of wear. Equipment collected airborne dust samples and fines during and after cutting for qualitative and quantitative characteristics. Analysis of collected dust revealed the dust's characteristics, including the concentrations, silica contents, particle size distributions, and particle shapes. Findings indicated that the dust generated in the cutting process increases as the pick tip wears. With a superimposed circle at the pick tip, further analyses show that as the tip radius increased by one millimeter during excavation, the dust generation at the pick increased by an average of 50 mg/m3 for all the samples. Furthermore, analysis of the cutting forces and specific energy of cutting (the amount of energy used to excavate a unit volume of rock) show that as the pick radius (mm) increases, the concentration (mg/m3) of dust per specific energy (kW-hr/m3) increases linearly. The correlation between dust and specific energy showed an average increase of 3.0 [(mg/m3) / (kW-hr/m3)] / mm of tip radiusin the rock samples tested. In terms of silica, the silica content is a function of mineralogy, and all the rock types contained traces of quartz. The airborne respirable particle size distributions insignificantly shifted between pick wear. The fines size distributions slightly increased as the pick wear level increased. However, the differences are also deemed insignificant and, therefore, are negligible. Finally, the pick wear does not influence change in the particle shapes. All the picks consistently generated suspended respirable particles with similar particle shapes that are slightly oval with mostly smooth edges.
    • Aging effects on sheared edge formability

      Findley, Kip Owen; Carley-Clopton, Aiden; De Moor, Emmanuel; Matlock, David K. (Colorado School of Mines. Arthur Lakes Library, 2023)
      Advanced high strength steels (AHSS) combine high strength with good formability, making them an appealing class of materials for the automotive industry. Despite good global formability, many AHSS grades have poor sheared edge formability. Additionally, previous studies have documented that sheared edge ductility, measured via hole expansion ratio (HER), changes with room temperature aging time between blanking and testing for several AHSS grades. The present study designed experiments to investigate strain aging and hydrogen embrittlement as possible mechanisms. Five steel grades were tested to evaluate effects of microstructure, tensile properties, and aging temperature on aging sensitivity of sheared edge formability. These steels include dual phase (DP), complex phase (CP), bake hardening (BH), cold rolled martensitic (CRM), and transformation induced plasticity (TRIP) aided bainitic ferrite (TBF) grades. Edge formability was measured via HER, with aging times of 0.5-240 h between punching and testing. Hydrogen embrittlement and strain aging effects were examined by: applying elevated temperature treatments during and before aging, measuring hydrogen content of different conditions, masking the sheared edge after blanking, and testing burr up and burr down. To investigate Zn coating effects on aging sensitivity, aging effects were measured for DP 800 specimens produced in an annealing/galvanizing simulator with the same thermal history and different coating and atmosphere conditions. No consistent microstructure or tensile property effects on HER or aging sensitivity were found. Of the grades in the comparative study, the CP and CRM grades experienced aging effects on sheared edge formability. The HER of both grades increased in the first several hours of aging, followed by a decrease out to 240 h of aging. Aging temperature impacted the rate of HER loss significantly for the CP grade, but had less of an effect on the CRM grade. A heat treatment which elicited bake hardening in tensile specimens of the BH grade did not change the HER of that grade, suggesting strain aging in the sheared edge does not necessarily reduce HER. The addition of a Zn coating incited aging sensitivity in the DP 800 grade, but a Zn coating was not necessary for a steel to experience aging effects, as exemplified by the CRM grade, which likely has the highest hydrogen embrittlement susceptibility of the grades tested. Overall, the results suggest internal hydrogen is responsible for aging effects.