Exploring the extraction of critical minerals from lignite coal

The University of North Dakota has been awarded an $8 million grant from the U.S. Department of Energy to study the extraction of critical minerals from coal. (Image from Shutterstock.) Researchers sometimes toil away without much to show publicly for their efforts. Other times, one exciting breakthrough leads to another, and government support and funding comes through. This is the case with the study of critical minerals found in lignite coal in North Dakota by researchers working at the University of North Dakota (UND). Mining Engineering recently spoke with Nolan Theaker, senior research manager and principal investigator at UND’s Institute for Energy Studies (IES) about these efforts. IES focuses on the integration of energy education, research and outreach. Its mission is to enable the development of the next generation of energy experts who can facilitate the advancement of energy technologies that are economically competitive, reliable, sustainable, and politically and environmentally acceptable. UND was recently awarded an $8 million grant from the U.S. Department of Energy (DOE) to further studies being conducted on extracting critical minerals from lignite coal, and to explore the possibility of creating an extraction and refinement facility in the state. UND researchers have been exploring different aspects of extraction from lignite since 2016, when IES received its first grant award from the federal government toward this effort. The “green” evolution and government mandates and commitments from businesses to reduce their carbon footprints, the development of electric vehicles (EVs), and geopolitical events happening around the world are partly driving these investments, along with the need to develop extraction and production facilities for critical minerals in the United States. Currently, it is estimated that nearly 85 percent of the processing of critical minerals is done in China. The United States wants to establish its own facilities for national security reasons and to have access to the use of these critical minerals right in its own backyard. “This latest grant is the logical follow on to research we’ve been conducting for seven years,” said Theaker. He is quick to point out that UND researchers could not have come as far as they have without tremendous support from their colleagues throughout the state of North Dakota, including those at the North Dakota Department of Mineral Resources and the North Dakota Geological Survey. Theaker has worked closely with Ed Murphy, North Dakota state geologist, on this research too. “I’ve gone out sampling coal with the state geologist. We take eight people out with pickaxes and shovels and we sample coal across a wide area,” he said. “We’ve had tremendous support from the North Dakota industry. Every power plant and mine in North Dakota has made this a priority, and the grant would not be possible without that support. We are all looking into: How do we produce rare earths?” said Theaker. Theaker explained that the team has started its exploration by building a pilot program. “We are still in this beginning phase, but we have had our eye on the future the whole time,” he said. The IES team consists of about 12 other researchers and 20 to 25 graduate students, who also collaborate with a number of small businesses and industrial partners. For this grant funding project, UND is now off to the races and will compete with West Virginia University (WVU), where researchers were also awarded $8 million in DOE funding. UND will study coal and extraction from lignite, while WVU is looking at acid mine drainage. Theaker said both universities will start getting the funding from these grants this summer or fall, and Theaker anticipates quick-turn requirements from the U.S. government. The teams will each have 15 months to complete their plans and submit findings and recommendations to the DOE. He anticipates the project will probably be completed by the end of 2024, and if they are granted the next phase of funding, groundbreaking on the facility will happen in the middle of 2025. “Our research is in extracting the rare earths from lignite coal and the precombustion coal. Unlike higher-rank coals, or many hard-rock minerals, the rare earths and critical minerals in lignite are not bound up in mineral form. They are actually bound on the organic structure of the coal, and so it’s far easier to extract them in that form,” Theaker said. “It’s far quicker, less chemicals are required, you’re able to do it relatively efficiently, and you don’t have to compete with the minerals — pyrite, clays, etc., in the coal. So it’s a unique rare earth resource opportunity that we have.” Theaker explained that when it comes to extracting from the coal itself, if it is all burned and the carbon is gone, the rare earth content of that material goes up. However, then the organic character, which is the basis for their extraction technology technique, is destroyed, and the rare earths have to be dissolved through glasses of ash. “Whereas for us, in that organic phase, it’s just washing over the surface of this porous lignite — we treat it like a sponge, washing over it with an acid, and all the rare earths peel off almost instantaneously,” said Theaker. “So it’s not digesting it over long periods of time. This is very, very fast that this happens, which obviously gives us some benefits.” When Theaker and his team started this research in 2016, they did not expect the coal to be in the form they found it. “We just knew from UND’s experience that we’ve seen rare earths in lignite coals. We know they can be there, so let’s just look into it,” he said about their exploration process. “And once we realized, wait, they aren’t in minerals … let’s do tons of computercontrolled scanning electron microscopy and look everywhere for these minerals. Oh, we are not finding many of them, even though the coal says there is still lots of rare earths there, where are they? We found it in this organic phase, and we found it’s a lot easier to extract than we expected, and so that’s where we’ve been going from here.” Rare earths found in coal The researchers are finding the whole batch of rare earths in the coal they are studying. These include the lanthanides, scandium and yttrium, which is typically found in organically associated forms in lignite. They are finding the coal is more heavily rare earth enriched too, so everything essentially to the right of gadolinium on the periodic table is being discovered. The lanthanides are enriched with extra terbium and extra dysprosium too — magnet rare earths that are of high value. Some of the light rare earths are being discovered as well, but the fact that they are heavy rare earth enriched is the unique piece of this puzzle. Three extra critical minerals being extracted from the samples are cobalt, germanium and gallium, with the last two being by far the outstanding critical minerals of value. When asked where they are getting the coal for study, Theaker said, “North Dakota has done a phenomenal job throughout the years with being very responsible with mining, and really doesn’t have tailings or waste. There are some abandoned mines, typically from homeowners that would dig up some coal for their stoves in the winter, but in large part, there really are not waste piles, there are not tailings piles, it’s been managed very well. I have to congratulate North Dakota for that.” A sample product developed from lignite at UND’s Institute for Energy Studies. Right now, the rare earths these researchers find in the lignite are concentrated at the margins of the seams — typically right at the top or right at the bottom. “That’s typically not what a power plant wants to burn. There is going to be some higher ash, some weird elements in that they do not want to burn, so that is still wasted. They will dig it up, pile it off to the side, and then dump it back into the pit. It’s still coal, it still has a thermal value and can be made into products, but is currently unused,” said Theaker. What the IES team is proposing is that during that cleaning section process of the mining, they take that lignite, which has a bit of overburden with it that is typically clay and is quite denser than the coal, and physically process it to concentrate the coal and extract the rare earths. In effect, then what was wasted and tossed into the pit is not only good coal that can be burned, but better than the thermal coal that would be beneath it. “It’s more reactive, it has less of the fouling constituents that North Dakota boilers uniquely have to deal with, such as sodium, and it’s more reactive for carbon product usage,” said Theaker. For example, the team has a couple of projects attempting to make graphite for batteries from the material, which is another interesting aspect they are finding with potential high value. “We are using the coal itself, but we’re using the sections of the coal that’s thrown away. We’re not competing with power plants for use either, if anything, we’ll be giving them more than what they already have,” he said. Is it new to find these structures in coal? From what Theaker can tell by looking at old reports at UND, where others have looked at lignite and the trace minerals in it, researchers have known that rare earths can be found here, but typically, it was looked at for what is in the ash, or what does this power plant produce? “We are talking about the top foot, the top six inches of these coal seams, those cleaning sections that have all these rare earths … if I mix in the bottom 6 m (19 ft) below that, the total rare earth content really isn’t that interesting,” he said. “So we knew the rare earth elements were there and once we actually started looking for them — we found them at those margins — we realized those margins are already there in the mining sequence, and they throw this away, they don’t actually recover this, this looks like an interesting opportunity. That’s where we started pursuing down this path,” said Theaker. “The DOE funding thrust to find domestic materials helped spur this on.” Building a critical minerals facility Barr Engineering is the primary lead on the architecture, engineering and procurement of building the facility. UND is also partnering with McCarls, an industrial and mechanical contractor out of Beaver Falls, PA, and Rare Earth Salts from Beatrice, NE. Rare Earths Salts is standing up a new electrochemical-based refining process that is all water based with no organic solvents, which Theaker said is a step change technologically as well as environmentally in the mineral refining process. Rare Earth Salts will refine the concentrate produced from the lignite. Additionally, Microbeam Technologies from Grand Forks, ND is partnered on this effort, providing ore sorting and engineering surrounding the critical mineral processing, as well as a host of industrial partners for commercialization. Theaker, a chemical engineer by training, explained that he worked in the solar fuels field in a job he landed through the University of Louisville, KY while pursuing his master’s degree. It was in that work that he gained an appreciation for the field of critical minerals and mining. He thought when transferring to UND five years ago that learning how to get these minerals out of the lignite would benefit the entire mining process. “If it becomes cheaper to extract coal, it benefits us all. This is about an environmental way of getting as much value out of as little disturbance as we can, as well as meeting the needs of these cutting-edge technologies — consumer technologies that have impacts, and trying to get as much of these rare earth materials as we can,” said Theaker. The questions the researchers are exploring today are logical follow-ons to the work they have been doing for seven years. They have discovered, “Can we find the rare earths? Yes. Can we extract the rare earths? Yes. Can we scale this up, and does it make economic sense? That’s what we are looking to prove in this next grant,” said Theaker. “In 2016, when we started this, I don’t think anyone would have thought, let’s see if we can build this facility. Now we are asking: What is the engineering design? Is this feasible? Phase 2 is actually building it, actually running it, actually produce rare earths from the facility from these mine waste materials,” he said. The pilot facility developed by the team at UND. A photo of the Falkirk Mine near Underwood, ND. Where will the facility be built? Lignite coal has a lot of water and there is no point in shipping water around, said Theaker. Like power plants that are built right beside a mine in North Dakota, this critical minerals processing plant would be built right beside a mine. The coal that the team produces could also be used for fuel or other carbon products. “If they wanted to burn it, we could sell it right away; sell the coal back to the power plant for fuel or other carbon, it would be right there,” said Theaker. “If we wanted to make an activated carbon product like graphite, we could do that on site as well, as it would be an industrial area already. It’s not a green field, it would be a brown field, for other activities,” he said. Two primary facility locations are being explored for this extraction facility: Falkirk Mine near Underwood, ND, and Center Mine, near Center, ND. Those two facilities would each produce a concentrate that would then be sent to Nebraska for refining to separated rare earth oxides. From the start of the research, the team has been trying to get as much value and understanding as they can out of what they do. “Our thinking was, we already dig up this coal, so if we can get the rare earths out, great. Then we looked at getting germanium and gallium and cobalt out, and realized that would make more money. And then we looked at, this can actually be used to make graphite, and that would get even more value,” said Theaker. Theaker’s advice to other researchers? “If you have coals, if you have other organic resources, go ahead and just check, see if there are critical minerals in there. Yes, DOE has done a lot of work looking at it, but if you are a mine geologist and have a coal seam you have been digging up, throwing away, go ahead and do a quick analysis, you might be surprised at what you find. Our technology can extract it pretty easily, and it is worth taking a look.” For young people considering working in the mining sector, Theaker said, “I can identify, because I started at age 22. It is an exciting area. There’s a million different paths you can go down — developing new technologies, finding resources, you can do many things, and it opens many doors in different areas to focus on. There is a lot of work to be done in a lot of different ways. This field is not fully researched; this field is not done. This is not a known problem or a known solution where we know how to mine rare earths or critical minerals. Mining technologies change all the time. How we mine today is completely different from 30 years ago, and completely different from 30 years before that. There’s not going to be a point where mining doesn’t have new problems needing new solutions.”

Exploring the extraction of critical minerals from lignite coal

Authored by:
Nancy Profera

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