Mine Tailings Beneficial Reuse
Mine tailings represent one of the greatest current challenges in the mining industry as they present both a safety and environmental hazard to mine locations. In this Senior Design project, the team was tasked with finding a beneficial reuse for mine tailings operated by Nevada Gold Mines. The reuse solution should be lower risk and cost than current tailings facilities. The team spent the Fall 2020 semester researching existing tailings reuse options and generation potential tailings reuse options to explore further next semester. The options explored for tailings beneficial reuse were basalt fibers, drilling mud, sea barriers, concrete, phytoremediation/phytostabilization, and fertilizer. These solutions meet the client needs and do so by using transforming the tailings into a new and hopefully profitable product for the client. After researching these options, the team performed an initial risk mitigation analysis and determined the future plans for pursuing each reuse option in greater detail. The team plans to incorporate feedback from the initial reuse options to guide the plan for next semester.
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Meeting ID: 969 2771 6256
- Zach Archibald
- Billy Beasley
- Jasey Diaz
- Wyatt Ellison
- Ashley Grob
- Sean Pearce
- Kaitlyn Bullock
Project Advisor: Robin Bullock
Technical Advisors include:
- Dr. Priscilla Nelson – Department of Mining Engineering at CSM
- Dr. Katha Pfaff – Department of Geology and Geological Engineering at CSM
- Dr. Matthew Posewitz – Department of Chemistry at CSM
- Dr. Bill Eustes – Department of Petroleum Engineering at CSM
- Dr. Reza Hedayat – Department of Civil and Environmental Engineering
- Dr. Lori Tunstall – Department of Civil and Environmental Engineering
The client established some key considerations for the team:
- Construction of tailings dams are the conventional form of disposal and are:
- Pose long term risks
- Drain down management
- Solution release
- Additionally, internal and external stakeholders ranging from operators to communities
After meeting with the client the following criteria was established:
- The project would focus on Nevada Gold Mine Tailings, therefore some proposed solutions may not be applicable for other types of tailings.
- Address and establish the:
- What is it?
- How is it created?
- Why is it needed?
- Where is it produced?
- who is it produced for?
- Risk identification and analysis includes:
- Applicable laws and regulations
- Environmental impact
The following criteria is what guided the teams research and proposed solutions.
The team came up with following ideas based off of research and projects on similar ideas:
Basalt or Glass Fibers
Basalt fiber is a composite that is similar in composition to fiberglass and carbon fiber. Basalt fiber has many useful properties such as great fire resistance, better physico-mechanical properties than other fiberglass, high durability, and overall low cost of manufacturing. Basalt fibers also see a lot of use across industry including, but not limited to, high-end concrete manufacturing and asbestos replacement.
Basalt fiber is manufactured by first crushing and melting basalt tailings at a sustained temperature of 1500C. This process can take multiple hours as a result of basalts high opaqueness and inability to transmit infrared energy. Additionally, basalt has a very low thermal coefficient, thus requiring large quantities of energy to melt in traditional conventional furnaces. The length of this energy intensive process can be greatly reduced by engineering a process using uniform heating elements such as electrodes. Once the temperature of the molten mixture is homogeneous, the basalt fibers are created by continuously extruding the molten basalt through platinum-rhodium bushings. The fiber can either be left and sold as is, or can be woven into a fabric to be used in similar cases to fiberglass or carbon fiber.
Overall, this would require the construction of a small furnace plant in order to melt and extrude basalt fibers. The upfront cost would be large but basalt fibers yield a high profit margin.
Drilling muds are fluid mixtures that are used in oil and gas drilling operations. It is pumped into the wellbore to prevent the inflow of fluids from permeable rocks that the bore is slicing through by forming a seal, maintain overall well stability, and carry cuttings and suspend solids from the cutting process. Drilling fluids vary by well type, but typically have a base fluid (usually water) along with a solid component that is added for the desired chemical properties. Insoluble high-gravity solids (HGS) are added to the drilling fluid to add weight to the fluid for desired properties such as viscosity and gel strength. Although drilling fluids typically have a complex chemical composition that is typically protected by intellectual property restrictions, they typically have a clay base with HGS materials that include barite, calcite, and dolomite.
Many of the common HGS materials used in drilling fluids are also found in the composition of mine tailings. Drilling fluids require finely ground solids, as coarser materials will effectively plug the fluid in the well and create problems during drilling. The cost of drilling fluids largely comes from purchasing the HGS materials, which have to be a very specific composition and a very small particle size which is cost-intensive to make. Using materials from mine tailings in drilling fluids would take advantage of the costs already incurred to process ore by reducing the particle size. The idea of using mine tailings in drilling fluids would be novel in the petroleum industry, presenting a brand new potential market for Nevada Gold Mines to capitalize off of tailings waste. Dr. Bill Eustes, a professor in Petroleum Engineering at the Colorado School of Mines, confirmed that this idea is new to the industry; he had previously considered it but did not have the access to mine tailings to research it further.
A production and processing facility would need to be built at the mine in order to turn mine tailings into material for drilling muds on site. Since the exact chemistry of drilling muds varies by company and even by well, the drilling mud is typically formed by mixing the required materials on site. This processing and production facility could produce the materials to be shipped out to form drilling fluids. To reduce transportation costs, it would be the most economical to focus on making materials to best suit the surrounding oil and gas operations in nearby states such as Wyoming and Utah, although other alternatives (such as fluids for offshore drilling) will also be explored.
The proposed solution of sea barriers being implemented in areas of rising ocean levels very much depends on the proposed solution of utilizing the tailings within concrete. However, it does not solely depend on this same proposed solution, it is a bit more difficult to implement due to the leaching potential of the metals within the tailings, which will be tested with an Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) test early next semester most likely. The strength of these sea barriers would need to be very strong, which would be tested within the concrete solution. The next step to trying to implement the sea barriers would be testing this concrete if it exposed to salt water and seeing if any sort of contamination came out of the concrete.
Phytoremediation is a type of bioremediation that uses plants for the removal of various harmful contaminants traditionally in soil. Phytostabilization is a subset of phytoremediation and involves the reduction of heavy metals in soil through methods such as minimizing erosion, decreasing wind-blown dust, and reducing contaminant solubility or bioavailability in the food chain.
Of all the options our team is considering, these methods are likely less promising than some of the others. These methods would not directly result in the production of a new solution, though could have potential in aiding other solutions. An ICP test would be helpful moving forward in determining if this could even be a viable solution. Much is unknown about the capital cost primarily due to uncertainty in what scale a technique like this could be implemented at.
The use of tailings as partial or full replacement in aggregates has been expanding the past decade, and research has already shown that it is a safe, viable option. One of the benefits within the cementitious materials industry is its focus on sustainability. Solid wastes such as fly ash and ground granulated blast furnace slag have been utilized in large amounts in concrete already, so clearly, the idea of expanding to mine tailings is not very far fetched. This option can also open many doors for us, because there is an endless amount of opportunities when it comes to concrete. We could use the tailing/cement mixture as jersey barriers for roadways or for sidewalks and walkways at the mining site. These are two great options because minimal leaching of the metals in the tailings will not lead to drastic issues. We would be more concerned to use the cement/ tailing mixture for concrete that is placed in a residential building or as the foundation for buildings. This is due to the fact that there is very little research on the long lasting effects of leaching on humans and because some studies suggest that tailings may decrease the compressive strength properties of concrete.
This is a very promising solution that the team is planning to further research. There are two professors here at Colorado School of Mines that are currently working with tailings in cement. Dr. Reza Hedayet is working with UNSA artisanal gold miners to research further processing of tailings to gather more gold. He is also looking into the effects of mercury and cyanide leaching. His overall goal is to produce civil construction materials from the tailings/cement mixtures. Dr. Lori Tunstall is also looking at the cementitious route and is looking to use the tailings from phosphate mines. Both of these professors will be invaluable to us as we continue our research, and they will provide tremendous insight. We can also look to another senior design group that has begun testing on using the tailings as the aggregate in concrete to see how strength is affected. These resources will be useful to help us decide whether we would like to pursue this option.
One of the initial ideas the team came up with was the possibility of turning the tailings into fertilizer. Fertilizer is important since agriculture leads to soils being depleted and fertilizer can provide enough nutrients for the next harvest. After speaking with Dr. Priscilla Nelson, a CSM professor in the Mining Department, she seemed to think it was a good idea. However, she did state that phosphogypsum tailings could be a result of producing fertilizer. However, with testing the team can see if these tailings are produced as a result of producing fertilizer. Additionally, an idea for the use of these tailings, if they are in fact a by-product, is to use them in compost. Gypsum is commonly used to be made into sheetrock/drywall therefore, these tailings could also be turned into drywall or used in the compost if the quality is not to drywall production standards.
This led the team to speak with Dr. Matthew Posewitz, a CSM professor in the Chemical Engineering department, who stated that fertilizer production seems like a viable option. He stated that three critical things must be considered, do the tailings have what the plants need? Which leads to the question of what is in the tailings? And lastly can biology access it?
There are a lot of carbonates in tailings and plants love it. It is important to know what is in the tailings to see if biology can access it and able to uptake in water. There needs to be a happy medium/sweet spot; a Goldilocks spot of not too much or too little of one thing. Plants usually like 16 nitrogen to 1 phosphate. However, if the tailings are deficient or have unwanted constituents the tailings can be augmented. In particular, it is important to know if there are any “toxic piggybacks” in the tailings. For example, plants cannot tell the difference between arsenic and phosphate at times. Heavy metals are also a concern, in particular cadmium, magnesium, and selenium. Dr. Posewitz is interested and would like to get involved. He has recommended ICP-AES testing and just using the tailings to see if plants can be grown. The team will be growing native Nevada grass (according to the Bureau of Land Management) and make qualitative observations such as plant mortality and height.
The team will narrow down the proposed solution through research and testing. The final proposed solutions will be presented next semester (Spring 2021).
The teams next steps include the following which will be completed throughout the end of Fall 2020 and starting Spring 2021:
- Prep and test tailings for ICP-AES testing for next semester for fertilizer, phytoremediation/phytostabilization, and sea barriers
- The ICP-AES test will help the team identify what are in the tailings and if the tailings have to be augmented
- Run concrete compressive strength tests and allow for 28-day curing period
- Continue the growing and observing of plant growth test for fertilizer
- Particle size and shape distribution analysis for drilling mud
- Researching further on all solutions
- Updating decision matrix
- Updating risk identification and mitigation
These next steps were determined through research and advice from technical advisors.
Meet the Team
Zach is an Environmental Engineering student graduating in May 2021. His engineering interests include site remediation, hydrology, and water quality consulting. He has worked with Pioneer Technical Services, an environmental and civil engineering consulting firm in Butte, MT, the past three summers working on a variety of different projects. Surveying, material testing, surface and subsurface sampling, well development, and piezometers installation are some of the experiences that he has gained working for Pioneer the last few years. Zach is a member of the Mines men’s soccer team and enjoys skiing, basketball, and wakesurfing outside of his studies.
Billy is a Mechanical Engineering student graduating in May 2021 from Mines. His engineering interests include projects with a strong business component, using feedback from the field to improve projects, and ropeway technology. His most recent work experience was an internship with Pyxis AI, a start-up that is producing AI software for ski lift controls to make them safer. He also spent 2 summers working with the Lift Maintenance department at Vail Mountain. Outside of school, Billy enjoys skiing, golf, running, and watching his favorite sports teams.
Jasey is a senior graduating in Fall 2020 in Environmental Engineering. She was born and raised in Colorado. She has experience with passive water treatment and is particularly interested in sustainability, remediation, and renewable energy.
Wyatt is an Environmental Engineering student with a minor in Engineering for Community Development graduating in May 2021. His engineering interests include sustainable design, environmental justice, and water quality consulting. His most recent project experience was working in collaboration with graduate students and professors from different universities on a National Science Foundation funded project looking at improving the water treatment process for artisanal and small-scale gold miners in Andes, Colombia. Outside of school, Wyatt enjoys running, basketball, soccer, and cooking.
Ashley is a Civil Engineering student with plans to pursue underground tunneling upon graduation. She has previous experience working for a tunneling company in San Diego, CA. In her Civil Materials class she worked on a project to test the plausibility of replacing the fine aggregates of concrete with tailings to understand how the compressive strength is affected. Outside of school she enjoys painting, camping, and spending time with friends and family.
Sean is a Senior Mechanical Engineering Student with an area of interest in automotive design. He has previous job experience in factory layouts, lean manufacturing, and part design working with Nutrien. He also has some experience working with the formula SAE team at Colorado School of Mines as well as class/lab experience working with engines. Sean will be graduating in Spring 2021 and will be looking for a job in Colorado. For extracurriculars, Sean loves climbing, hiking, and skiing in his free time.