Scattered through the coal country of Appalachia are heaps and hills of tailings – material left over after separating out the coal. Long seen as worse than worthless, they are sources of contamination.
Aaron Noble sees the hazard, but he also sees an opportunity. Noble and other Virginia Tech scientists are studying methods of extracting critical minerals from tailings and another waste product called acid mine drainage. Amid rising concerns over our dependence on foreign sources for rare earth elements, Noble and his colleagues are laying what could be the groundwork for a new industry.
“What we focus on, primarily, is a group of elements called the rare earth elements,” Noble said in an interview in Virginia Tech’s Holden Hall. “And I always say, they’re the nether regions of the periodic table, right? We learned about them in grade school, and then most people don’t ever think about them again – yttrium, lanthanum, cerium, neodymium, praseodymium.”
Despite their name, the 17 rare earth elements are relatively abundant in the earth’s crust.
According to a 2019 article by Russell Parman that appeared on the official Army website, “where ‘rare’ comes into play is that, in contrast with ordinary base and precious metals, rare-earth elements have little tendency to become concentrated in exploitable ore deposits. Consequently, most rare earths come from a small number of sources.”
When separated from ores into elemental form, they appear as gray, lustrous metals that are typically soft and malleable, according to the National Minerals Information Center.
In 2021, Chinese mines produced 168,000 metric tons of rare earth oxides, while the U.S. produced 43,000 tons, according to the U.S. Geological Survey, Mineral Commodity Summaries, January 2022. (A metric ton equals 1,000 kilograms.) Reliance on imported rare earth compounds and metals for 2021 was greater than 90%.
“Everything from GPS navigation capability, cell phones, fiber optics, computers, automobiles and missiles relies heavily on rare-earth elements for development and production,” the Army article stated. “High-strength rare-earth magnets have allowed numerous electronic components used in appliances, audio and video equipment, computers, vehicles, communication systems and military gear to be miniaturized.”
The bottom of the rare earth supply chain is the concern of Noble.
“If you look at conventional mining, like open pit or underground mining, that’s one way of acquiring critical minerals,” said Noble, an associate professor in Tech’s Mining and Minerals Engineering department. “And we do a little bit of work in conventional mining methods.
“But we also look at unconventional resources. Because there’s a lot of opportunity, I think, in unconventional resources, to have better economic, better social and better environmental outcomes.
“So in the case of coal, oftentimes, based on the mining method, we may mine a third to a half of the material we take as coal. And the other half may be clays and shales, things we don’t want. So at the mine site, we’ll separate that out and produce a tailings product, which is usually some sort of clay or shale. In Appalachia, through hundreds of years of mining, there’s quite a bit of tailings and they’re kind of these legacy environmental issues.
“If you go back to the older stuff that’s 100 years old, the mining practices weren’t as efficient. So there’s more tailings from the older sites than there are the newer sites. And what we’ve looked at is, how can we turn that environmental liability into a resource, and particularly into a resource for critical minerals for things that society really values? And when we started on this back in 2016, we knew that there were critical minerals in coal and coal waste, but we had no idea how to extract it and process it.
“A lot of my research focuses on the central Appalachian and northern Appalachian basins. And we’ll work with industry partners or we’ll take samples ourselves … I think the last sampling effort we did, we recovered maybe 10 barrels of material from a site and brought it back.”
Small scale work happens in the E. Morgan Massey laboratory in recently renovated Holden Hall. Pilot-scale testing is conducted in a facility on Plantation Road. “So there we’ll be processing hundreds of pounds, to tons, of material there.
“Many of our processes start with crushing and grinding the sample. Ideally, we don’t like to do a lot of crushing and grinding, because it can be expensive, and it can be a costly step. So if we can find a sample, like tailings, that are already very fine, then you don’t do a lot of crushing and grinding. But you may do that to start just to prepare the material.
“We then like to do some concentrating. That reduces the volume for your downstream steps. And that’s the whole name of the game, is reducing that volume with each step. Because as you go further down that processing train, everything gets more expensive. So you want to send less volume to the next process. And then usually the business end where you really get into the nitty gritty is through some sort of extraction step where you take the rare earths or critical minerals that you’re interested in, and you want to dissolve them into solution.
“Once there are dissolved species in solution, then you can more easily manipulate the chemistry. They become a lot easier to work with. That extraction step tends to be one of the more challenging and more costly steps. And it’s a place where understanding the science is really what enables you to do that effectively.
“So oftentimes the extraction is done in an acidic solution. You can use strong acids and get high recoveries and high yields. But our goal is to step back from that and say, how do we use the least aggressive approach that gets us to some optimal result, that balances cost, environmental impact, waste generation and production rate?”
Some rare earth mining does happen in the United States, Noble said. Rare earth concentrates are sent to China, where they are processed and used in manufacturing. China then sends the finished products back to the U.S., “usually in the form of an iPhone, or an electric vehicle or a motor, not in terms of intermediates; they usually control not just the processing, but then the manufacturing as well.”
One of the key rare earths is dysprosium, which is used in permanent magnets to maintain performance in high temperatures.
“So if you look at things like electric motors, and magnets needed for power generation, say in a windmill, they need to be able to operate at higher temperatures, so they need quite a bit of dysprosium.”
In addition to coal tailings, Noble is studying acid mine drainage as a source of rare earths. A byproduct of some mining processes, acid mine drainage contains sulfuric acid and dissolved metals.
“If you look at mining practices from 50 to 100 years ago, they didn’t have a good handle on how acid mine drainage was generated, and how to treat it and how to capture it,” Noble said. “Working with some of my colleagues, we looked at acid mine drainage and actually found it to be … a very concentrated source of rare earths. It may be our grandfathers’ mining practices have done the first step for you. And so we come in and capture acid mine drainage and treat it in a way that will concentrate rare earths while producing clean water.
“And if you start putting these together, so you have coal tailings, you have conventional resources, you have other waste sources, industrial wastes, you have acid mine drainage, you can see kind of this all-of-the-above approach to how we could build an industry of producing rare earths here in the U.S., because it has to start at the front of the supply chain … and then our goal is, how then do we do the next step and do the separation and refining. And if we can do that, then we can produce products that can be sold to support U.S. manufacturing of some of these high-end electronics.
“So the processing technologies we’re developing, that’s what’s going to enable that industry to develop. And so it’s like, in some ways, we’re the missing link of making this whole thing work.
“The one thing I always tell people is research and development takes time, especially in this line of work. If you start thinking about the timeline to procure and do construction and installation, I think it’s reasonable to anticipate you could have demonstration scale production later in this decade, so 2027, 2028. If we look at completely offsetting Chinese production, that may be in the next decade.”
Noble’s work is supported by research contracts from the U.S. Department of Energy, as is the work of his colleague, Wencai Zhang, an assistant professor in Mining and Minerals Engineering. “I am trying to extract rare earth elements and other critical elements (e.g., lithium, cobalt, nickel) from various sources,” Zhang said in an email. “The major source materials that I am working on include coal-based materials (coal, coal waste, acid coal mine drainage), rare earth ores … and solid wastes (e.g., municipal solid waste incineration ash).”
A pilot plant in Providence, Kentucky is producing rare earth elements at around 100 grams/day, he said.
Among the novel methods Zhang is investigating is phytomining, the extraction of metals from plants that accumulate the metals in their tissues. “There are some plants showing very strong uptaking capacity of REEs [rare earth elements] from soils, so we are using the plants to enrich REEs. We are also developing methods to recover REEs from the plants after uptaking.”
In the same department as Zhang and Noble is Richard Bishop, a professor of practice. “Typically professors of practice have industry experience, which I do,” he said. “So it’s a non-tenure track position somewhat like an adjunct professor.”
Bishop is the principal investigator in Evolve Central Appalachia (Evolve CAPP), a two-year project funded by the Department of Energy. Evolve CAPP is identifying potential sources of rare earth and critical minerals in southern West Virginia, southwest Virginia, northeastern Tennessee, and eastern Kentucky. The Virginia counties are Buchanan, Dickenson, Lee, Norton, Russell, Scott, Tazewell and Wise.
“We’re also looking at economic development opportunities, existing infrastructure … perhaps government incentives that would encourage investment and development in the region. And so all the ingredients that would go to encourage having a strategic domestic resource available here in the U.S.
“There’s a lot of supply risk with critical minerals right now. The push and the desire for the country to move more into electric vehicles, and green energy, of course, has accelerated demand for a lot of these minerals that are sourced from, and we’re dependent on, foreign sources right now. The Evolve CAPP project is one of many projects sponsored by the Department of Energy right now.
“It’s a large team … of academics, policymakers, consultants with geology and mining backgrounds, individuals with experience in fly ash and coal combustion residuals from power plants. So we’re putting this large team together to try to really narrow down what the opportunities could be for this region. And even what some of the downstream applications could be of manufacturing opportunities.”
He believes it is “absolutely possible” that the groundwork being laid now could result in the development of a major industry.
“I think part of the key is also identifying incentives for capital to come in, or it may need to even come from government subsidies. It’s really hard to say at this point. It’s very easy for people who control the supply chain of these types of critical minerals to flood the market.”
Bishop did not mention that China has been accused in the past of depressing prices of certain commodities to discourage competition.
Even if rare earth production becomes economically feasible, it must meet environmental concerns.
“We are certainly open to hearing from all stakeholders in this region, so, of course, no mine will ever be built or anything will move forward without acceptance from communities,” Bishop said. “There’s a lot of advantages to having extraction here and local jobs here, but obviously, if people don’t want that in their backyard or don’t want those types of jobs, it will be harder to ever move forward on something like this.”
Bishop and colleagues are midway through the Evolve CAPP program, which concludes in September 2023.
“The hope is that this research will continue on beyond the next year, and we’ll be able to do a lot more, including further testing and sampling to essentially have a proper study of this region, whereas a lot of the work right now is looking at sources of existing information and putting all that together.”
Subodh Das, the CEO of Missouri-based Phinix LLC, is part of a consortium, also including Tech’s Zhang, that is researching rare earths on a contract from DOE’s Office of Energy Efficiency and Renewable Energy.
“The aim is not for Department of Energy to produce this material,” he said. “The ultimate goal is to de-risk the technologies,” so private companies will have the motivation to license the new processes and produce goods through the commercial sector.
In addition to any new process being economically and environmentally acceptable, “we have to have intellectual property so we can protect our technology. So no investor will invest in technology unless they feel this product is protected. Otherwise, somebody can replicate that, and we lose all the time and money and all that.”
Noble is focused on developing those processes, but he also sees the big picture.
“If you look long-term for national security, we need a supply of rare earths here in the U.S. so we can meet defense industry needs,” he said. “But then looking beyond that … I think there’s also a desire here to say we have an opportunity to go into mining districts that may have poor environmental outcomes, they may have these legacy wastes, they may have poor job opportunities, and really change that narrative, to say, hey, we can come in and clean up these legacy wastes. And we can create … almost a new industry in those regions focused on rare earth production and manufacturing. And in my mind, it becomes a real win-win. You can meet a national security need, and you can supply jobs to regions that are in desperate need of jobs, and you have an opportunity to support better environmental outcomes.”