Hunt for rare earth elements in North Dakota lignite coal goes underground
One clue the Geological Survey has for where the rare earths are is how far away a bed of lignite is from white clay.
Rare earths once sat on top of the white clay, but excessive heat around 55 million years ago during the 200,000-year "Paleocene-Eocene Thermal Maximum" (PETM) period caused minerals to leach beneath it. Many of these remain scattered in the ground, but some fell into the lignite coal beds, allowing them to remain in concentrated spots.
Today, these beds of coal are catching the attention of governments, businesses and scientists.
"Rare earths are not actually that 'rare,'" Moxness explained. "If you grind the entire surface of the earth, the rare earth concentration will be on average 180 parts per million." What is rare, however, are the large concentrations that have been found in lignite over the state's past decade of research. Coal formations with more than 300 rare earth parts per million could interest companies. Samples that state geologists have found in lignite outcrops in North Dakota's Badlands indicate that what the state has is much higher. But if a company wants to mine for rare earths in North Dakota, it would also likely need to see those large mineral concentrations across large volumes of coal. Determining where that is exactly, however, is still a bit of a guessing game."This is like prospecting," said John Mohl of Mohl Drilling, the company that won the bids to work with the state on the project. His son Jason Mohl, who was working on a separate rig nearby, is the company's president.
Clues from past drive mineral search efforts A small abandoned lignite coal mine sits near the rare earth search. It was dug before modern mining and environmental regulations went into place in the 1970s. What is left of the mine provided the state a clue of where to look for more coal.But there was not much luck at the day's first stop. As the drill traveled deeper and deeper underground, no coal was coming up.
Moxness said that the lack of lignite here is likely due to a river washing it over millions of years ago and leaving other minerals in its place. Whatever rare earths leached from the white clay during the PETM are now spread amongst the clay and other rocks, but not coal.
"That is probably why they stopped digging for coal here, too," Moxness said.
There is some continuity between the people who dug the now-abandoned mine and the crew looking for rare earths. Despite improvements in technology, many modern and relatively short-term material constraints remain subject to events that took place across geological epochs.
The drill got to around 120 feet below the surface without hitting any coal and just as Moxness was ready to call it quits on this hole, one of the drill operators noted a different feeling on the rig, indicating the crew finally hit some lignite. A mud sample that brought up chips of coal confirmed that that was the case. Moxness advised to drill just a bit deeper.
More coal rose but was not very thick, and its distance from the white clay meant that it was unlikely that any large concentration of rare earths settled there.
The crew took a log of the hole using a large metallic rod to measure the density and types of rock underground, but decided against taking a core - doing so is a time-consuming process, which in this instance would likely not have provided any useful information on the rare earth hunt.
"It's also good to know where the minerals are not," Moxness said.
Old and new North Dakota industries
While this one spot will likely not be the site of a future rare earths mine, the land already serves as a reminder of both old and new industries for the state - and the role that rare earths play.
The white clay where the rare earth elements once sat is the same material that the Hebron Brick Co. - North Dakota's sole brick manufacturer - uses to craft its product. This particular hole was being drilled at one of the company's clay mines.
When the drill was not humming, the sound of "moos" from cattle in nearby fields served as an almost immediate replacement.
And just a few miles away was a wind farm, where the energy from the wind turning the towers' blades is converted to electricity with the help of magnets that require rare earths for production. The vast majority of these minerals, however, come from outside the U.S.
The only commercial rare earth mine in the U.S. is Mountain Pass in southern California. But there, the rare earths are concentrated in hard rock, requiring intense chemicals for extraction. This makes for an expensive and at times an environmentally hazardous process. Though operational today, Mountain Pass has gone through numerous owners in recent decades and has struggled to keep the lights on while dealing with environmental issues and competition from China. What's found in coal seams could be cheaper to extract, according to recent research out of the University of North Dakota, and it could also create fewer environmental risks because the chemicals needed are much more watered down compared with hard rock extraction. A large concentration There was a bit more luck a few miles west of the first site. As the drill bit pierced the ground, the piles of mud that rose to the surface were darker than at the first spot, meaning that the coal at the new location is closer to the white clay, and likely full of rare earths. This time, the crew decided to take a core, using a 10-foot long barrel to pull rock from the earth. After the core got dug up, the team used an X-ray fluorescence (XRF) machine to get a quick estimate of the concentration of rare earths in the rock. The only rare earth element the XRF could pick up was yttrium - "Y" on the periodic table - but since the elements tend to travel in groups, the parts per million of yttrium can be multiplied by a factor of 10 to get an early sense of the total rare earth concentration. The XRF measurements read 616 parts per million of yttrium, meaning the concentration of rare earths could be higher than 6,000 parts per million, but Moxness said that is probably not an accurate estimate. This coal could just have very high levels of yttrium. Still, he said a conservative estimate of rare earths in the sample would be around 3,000 parts per million. If correct, that is 10 times higher than what the federal Energy Department has indicated would make mining coal for rare earths economic. The core sample will be shipped to a private lab in Wyoming for more thorough testing. There was just one problem with the sample - it may be too small to be mined economically. The size of the coal in the core was only about a foot long. The largest sample of coal that the team found with a high rare earth concentration during its September drilling program was about two feet long. While Moxness and other state geologists continued to examine the core, another one got dug up. In the next attempt, the core extracted a much larger sample of coal from the ground - nearly 6 feet long - but measurements from the XRF showed it had scant concentrations of rare earths. The distance between this chunk of coal and the white clay was too great for significant levels of rare earths to have ever leached down and concentrated there. Companies might be interested in mining for something like the first sample, Moxness said, but it is much more likely that interest would come if his team is able to find a core that strikes the balance between the concentrations of the first sample and the size of the second. He is hopeful that it is out there. Life for lignite Moxness is not the only one who is hopeful. Lignite has been mined in North Dakota for over a century, but the industry's present makeup is mostly a result of a coal boom that began in the 1960s. Those boom days are past. It is now a tougher time for the industry. Economic and regulatory pressures in recent decades have made it harder to make money operating coal-fired power plants or build new ones. Mohl Drilling, the Beulah-based company running the rigs, usually works with companies that mine coal for power production, helping them with exploration on land near existing mines. Talk of rare earth mining has brought some excitement to Beulah, said Jason Mohl, the company president. He told the Tribune that his family business has operated in coal country for three generations now. "Everyone's hopeful it might keep the coal industry here longer," he said. A major federal investment could help too. North Dakota is competing with West Virginia for a $124 million federal grant from the Energy Department made possible through the 2021 Bipartisan Infrastructure Law which would provide 50% of the costs for building a facility to process the rare earths found in coal waste. None of that will happen overnight. The results of the testing done in Wyoming will be available in a report from the Geological Survey in the next couple of months. If the results end up piquing the interests of private companies, there is still likely a while to go, and a lot of work to be done, before there is any rare earths boom to speak of in North Dakota. "Setting up a brand new mining operation could take about a decade," Moxness said.Reach Joey Harris at 701-250-8252 or .
Energy/Environment Reporter
