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Browsing by Author "Bareither, Christopher, advisor"

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    Characterizing tailings professional labor demand
    (Colorado State University. Libraries, 2021) Spencer, Louise, author; Scalia, Joseph, IV, advisor; Bareither, Christopher, advisor; Sanford, William, committee member
    A low-carbon future necessitates increased extraction of critical minerals via mining. The act of mining includes not only extraction of commodities, but also management of tremendous volumes of waste. Despite the need for mining to support green technologies, mining is experiencing a credibility crisis due to historic legacies of environmental damage and recent catastrophic failures of tailings (mine waste) facilities. To regain social trust and environmental credibility, the mining industry must do better at managing tailings. The recently issued Global Industry Standard on Tailings Management (GISTM) places significant demand on tailings professionals worldwide. Given these pressures, this study addresses the question: is the current tailings professional labor pool sufficient to provide the specialized labor needed to meet new guidance designed to make tailings facilities safer, and if not, how can this shortage be rectified? To address this question, a coupled qualitative-quantitative approach was undertaken. Research was conducted to characterize the current (Spring 2021) industry practitioner perspectives on the state of tailings labor resources. Then, future tailings labor demand under the GISTM was calculated quantitatively by estimating professional labor demand based on guidelines presented in the GSITM and applied to the estimated number of tailings facilities worldwide. Finally, opportunities to address current and future tailings labor demand were identified through tailing practitioner perspectives. According to current practitioners, there is shortage of qualified tailings professionals, related to increased labor needs, difficulties of recruitment into and retention within the industry, as well as senior-level professionals retiring. Managing the minimum estimated 16,000 tailings facilities worldwide was estimated to require as many as 17,800 full-time equivalent, qualified and trained personnel. Finally, current actions to train future tailings professionals are provided, as well as recommendations for actions via collaboration between academia, industry, consultants, regulators, and non-governmental organizations (NGOs) to fortify tailings recruitment activities, training programs, and educational opportunities.
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    Hydrological assessment of field-scale GeoWaste and waste rock test piles
    (Colorado State University. Libraries, 2020) Hassanzadeh Gorakhki, Mohammad Reza, author; Bareither, Christopher, advisor; Shackelford, Charles, committee member; Scalia, Joseph, committee member; Heyliger, Paul, committee member; Butters, Greg, committee member
    Mine waste rock and mine tailings are generated in substantial quantities an d must be managed to protect human health and the environment. Challenges in mine waste management facilities include geotechnical stability, environmental contamination, water management, and post operation (long term) closure. Waste rock and tailings co-disposal is a management technique that can address many of the aforementioned challenges. GeoWaste is a mixture of fast-filtered tailings and waste rock blended to isolate waste rock particles within a tailings-dominated matrix. A field-scale experiment that included a waste rock pile and GeoWaste pile was conducted at a mine in Central America to evaluate if GeoWaste suppresses sulfide oxidation and production of metal-rich acid rock drainage relative to waste rock. The objectives of this study were to (i) evaluate hydrologic performance of the piles, (ii) conduct in situ infiltration tests on the piles, (iii) determine field-scale hydraulic parameters for GeoWaste and waste rock, and (iv) develop numerical models to predict water content and oxygen concentrations within the piles. Water content, temperature, electrical conductivity, and oxygen concentration within the piles were monitored for 26 months. Sealed double ring infiltrometer tests were conducted at the end of the pile experiment and test pile subsequently were excavated to assess the spatial distribution in geotechnical characteristics. Inverse modeling was completed in HYDRUS-2D based on infiltration data to determine hydraulic conductivity and moisture retention parameters for the test piles. Field- and laboratory-scale hydraulic parameters were used in HYDRUS-1D and HYDRUS-2D to develop seepage models to predict moisture movement during the 26-month pile experiment. Oxygen concentration was predicted for the GeoWaste pile in HYDRUS-1D via the solute transport module, Fick's 2nd law, the oxygen consumption rate, oxygen diffusion in gas and water phases, and Henry's constant.
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    Influence of co-disposing oil and gas exploration and production waste and municipal solid waste on hydraulic conductivity
    (Colorado State University. Libraries, 2022) Karimi, Sajjad, author; Bareither, Christopher, advisor; Scalia, Joseph, advisor; Sharvelle, Sybil, committee member; von Fischer, Joe, committee member
    The most common method of municipal solid waste (MSW) disposal in the U.S. is still landfilling. Co-disposal of MSW with other non-MSWs in solid waste landfills requires engineering design to reduce the risks associated with the stability and functionality of solid waste landfills. Hydraulic conductivity is one of the engineering parameters required to assess the stability of a landfill. This study evaluated the effects of addition of oil and gas exploration and production wastes (E&PW) to municipal solid waste (MSW) landfills on hydraulic behavior of mixed waste. Hydraulic conductivity of solid waste is a function of vertical stress, waste composition, mixture ratio of MSW to E&PW based on total mass (e.g., 20% MSW + 80% E&PW), and mixing methods. A series of laboratory experiments were conducted to assess the impacts of these factors on the hydraulic conductivity of solid waste. Exploration and production waste was prepared to two moisture contents for laboratory testing: (i) as-received, which had a dry weight water content of 18%; and (ii) wet, which had a target moisture content of 32% to 36%. Wet E&PW prepared to the water content threshold represented the upper bound of water content for which the HMW met regulations for direct disposal in an MSW landfill. Hydraulic conductivity of the as-received E&PW measured in a large-scale permeameter decreased from 7.3×10-5 m/s to 1.1×10-8 m/s with an increase in vertical stress from 1 kPa to 394 kPa. The ks of as-received E&PW in small scale a small-scale permeameter reduced from 1.2×10-7 to 1×10-9 m/s with increasing stress to 50 kPa, and then ks stabilized at 7.5×10-10 m/s with increasing effective stress to 400 kPa. Although ks of the small-scale E&PW specimen was two to three orders-of-magnitude lower relative to the large-scale specimen as a function of vertical stress, the data align when evaluating ks as a function of dry unit weight. This indicated similar response of small-scale and large-scale specimens to hydraulic conductivity with respect to dry unit weight. The effects of E&PW hydration can be observed via the wet E&PW. The initial dry unit weight of the wet E&PW specimen was approximately 14 kN/m3, with a ks similar to the trend in ks versus dry unit weight for the as-received (dryer) E&PW specimen. However, ks of the wet E&PW specimen reduced two orders of magnitude (6.6×10-6 m/s to 5.4×10-9 m/s) as the effective vertical stress was increased to 17 kPa and dry unit weight increased to 15 kN/m3. Subsequently, ks of the wet E&PW decreased one order of magnitude to 2.8×10-10 m/s as vertical effective stress was increased from 17 kPa to 389 kPa. The ks of the wet E&PW specimen was two orders of magnitude lower than as-received E&PW under 394 kPa effective vertical stress. The overall trends for all E&PW mixture ratios for both the as-received and wet E&PW were similar, and exhibited an as-expected decrease in hydraulic conductivity with increasing vertical effective stress. Hydraulic conductivity for MSW-E&PW mixtures with 20% and 40% E&PW contents reduced from 3×10-5 m/s to 1×10-7 m/s under effective vertical stress ranged from 0 to 400 kPa. An increase in the mixture ratio above 60% resulted in an additional order-of-magnitude decrease in ks to 1×10-8 m/s as vertical effective stress increased above 200 kPa. The lowest ks at each stress level was measured for MSW mixed with 80% wet E&PW. Findings from this study indicate that addition of an E&PW did not change the hydraulic behavior of MSW. Mixture of E&PW and MSW creates a waste matrix such that hydraulic behavior still is controlled by MSW components at low stresses (and low dry densities). However, if vertical stress exceeds 50 kPa, mixtures of MSW + 80% (and above) E&PW were observed to produce a low permeability (i.e., ks < 1×10-9 m/s). If the E&PW is disposed in discrete layers without rigorous mixing with MSW, increasing vertical stress may substantially reduce the E&PW hydraulic conductivity producing water and vapor barriers within the landfill. These findings represent the specific E&PW tested in this study, however, when combined with other data in the literature, illustrate the need for establishing mixture ratio thresholds and intentionally co-disposing E&PWs.
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    Influence of geochemical processes on geotechnical stability of tailings storage facilities
    (Colorado State University. Libraries, 2023) Orcutt, Heath Marie, author; Scalia, Joseph, IV, advisor; Bareither, Christopher, advisor; Ridley, John, committee member
    Incorporation of geochemically induced material changes and weathering patterns into geotechnical design and long-term stability analyses of tailings storage facilities has yet to be implemented widely or consistently. Tailings are deposited in disequilibrium with the surrounding environment and must undergo physical, chemical, and biological weathering to reach their most stable form. As a result, the geotechnical properties of the tailings (i.e., particle size, water retention capacity, shear strength, etc.) change over time. Herein, an in-depth review of published literature is provided, ranging across multiple disciplines (geochemistry, geotechnical engineering, hydrogeology, environmental engineering, mining engineering), and focusing on studies that document or allude to material property changes of weathered sulfidic base metal tailings. Synthesized visual aids are provided as a framework for beginning interdisciplinary conversation that couples geochemistry and geotechnical engineering. By drawing attention to potential geochemically induced failure modes, I hope to draw connections between geochemistry and geotechnical engineering that are fundamental to developing robust designs and advanced monitoring plans that ensure long-term tailings storage facility stability. A "proof of concept" laboratory design is presented which analyzes changes to the physical material properties (compressibility, permeability, and shear strength) of saturated fine-synthetic tailings mixed with calcite at different pH values. Overall, this report seeks to lay the foundation for future study and advance communication between experts.
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    Numerical and experimental evaluation of the erodibility of particle packings with surface treatments and spring reinforcements using the discrete element method
    (Colorado State University. Libraries, 2019) Peterson, Kirsten LaRhea, author; Heyliger, Paul, advisor; Bareither, Christopher, advisor; Atadero, Rebecca, committee member; Kampf, Stephanie, committee member
    Chapter 4. The erodibility of homogeneous two-dimensional spherical particle packings subjected to added mass surface treatments was explored using a combination of physical flume experiments and the discrete element method (DEM). Packings composed of spherical glass particles, with and without surface treatments and angled at two different slopes, were tested experimentally and simulated numerically under surficial flow conditions. The surface treatments acted to add mass to the surface of the particle packings. Particle erosion was quantified by tracking eroded particles as a function of fluid velocity. DEM simulations and flume experiments were first performed with a layer of steel particles that served as an extreme case of surface treatment. Similar trends were observed between the simulations and experiments, whereby the number of eroded particles decreased by an average of 90% when compared to untreated cases. The results from this surface treatment suggested that if the surface treatment mass is large enough, nearly all particle erosion under surficial flow conditions can be mitigated. Additional experiments were performed with surface treatments composed of increasing application rates of wetted agricultural straw. The particle erosion rates were dominated by piecewise linear behavior as a function of eroded mass versus fluid velocity. This behavior indicated a) an initial resistance to flow based on gravity, followed by b) a surface treatment movement that induced widespread failure or erosion at a much higher rate. Dislodgement and subsequent erosion of particles occurred at higher fluid velocities (over 50% higher for the highest straw application rate) when the surface treated cases were compared to the untreated cases. Conclusions drawn from the simulation and experiment results indicated a direct correlation between added mass on the surface of a particle packing and decreased erosion under surficial flow conditions and showed that as slope increased, erosion levels increased and began at lower surficial flow fluid velocities. Chapter 5. The erodibility of three-dimensional particle packings reinforced numerically with elastic springs and subjected to overland flow conditions was explored using the discrete element method (DEM). Particle packings at three slopes, subjected to overland flow at two fluid velocities, and four reinforcement configurations resulted in a total of 24 datasets of simulation results for comparisons to be made. The three slopes were composed of the same 2400 particles with coarse sand material properties and a uniform distribution of diameters between 1.8 and 8.0 millimeters. The elastic spring reinforcements represent a potential modeling technique for root development in a soil. The spring reinforcement technique presented here is a proof-of-concept attempt to model three-dimensional slopes at up-scaled particle sizes, root stiffness, and fluid velocities. Particle displacements were tracked and compared as functions of time, reinforcement level, and slope. The results suggest linear relationships between decreased particle movement with increased percent reinforced surface particles, increased particle movement with increased slope, and decreased sediment yields with increased percent reinforced surface particles. Also, at the lower fluid velocity, particle displacements were more dependent on incremental changes in slope; whereas at the higher fluid velocity, particle displacements were not dependent on small changes in slope. Overall, the results from the simulations and experiments showed the influence of elastic spring reinforcements on particle movements and the next step of the research would be to assess the scaling effects and apply the root model to smaller particles, more indicative of where roots are expected to grow.
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    Proposed laboratory investigation into electroosmotic dewatering of mine tailings
    (Colorado State University. Libraries, 2020) Vander Vis, Kimberly Ann, author; Bareither, Christopher, advisor; Scalia, Joseph, advisor; Sanford, William, committee member
    Geotechnical concerns of tailings storage facilities (TSFs) often depend on the water content of the tailings. Tailings with low hydraulic conductivity often have high-water contents with low undrained shear strength at the time of mine closure which limits the ability to close the TSF. The purpose of this study is to explore undrained shear strength gain in surficial mine tailings using electroosmotic dewatering (EOD) to help promote closure and reclamation of TSFs. Electroosmotic dewatering uses electrodes to apply an electrical direct current to induce flow through a porous medium. An experiment was developed to assess the effectiveness of dewatering methods at bench-scale to increase undrained shear strength of tailings via three different methods: EOD, surcharge consolidation, and evaporation only. The proposed research will evaluate if EOD (1) increases undrained shear strength of saturated surficial mine tailings more rapidly and (2) increases undrained shear strength as a function of depth more effectively, compared to the other techniques. Factors that influence EOD were preliminarily evaluated and include electrodes used, pore fluid chemistry, degree of saturation, voltage gradient and electrode configuration. Additionally, electroosmotic dewatering of mine tailings has not been implemented on a large-scale possibly due to lack of developed procedure, difficult water removal, and lack of a commercially available EOD unit. A goal of the proposed research plan is to develop field-scale implementation methods and water removal techniques via a moisture wicking synthetic capillary drain unit to be coupled with electroosmotic dewatering (i.e., EO-Plant) for field-scale applications.