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DOE looks to coal wastes to increase US supply of rare-earth elements

The US Department of Energy announced last month plans to offer $140 million for building and operating a plant that will separate rare-earth elements (REEs) from coal wastes. Those wastes, however, have low concentrations of REEs that are comparable to those in soils and rock, raising doubts as to whether such an operation could be economically viable.

In a 14 February request for information (RFI), DOE seeks public input on a provision in the Bipartisan Infrastructure Law that calls for construction of a “full-scale integrated rare earth element extraction and separation facility and refinery.” Responses are due by 31 March. The RFI will likely be followed by a solicitation for bids from industry to build the plant.

According to the RFI, industry will be expected to match DOE’s $140 million contribution. The goal is to economically produce 1000 tons of mixed rare oxides annually, about 10% of US demand, from coal wastes beginning in 2027–28. DOE hopes that production would expand to 10 000 tons by 2035, about 10% of projected US demand, and to 20 000 tons by 2040, or 20% of projected demand. The refinery could also produce unspecified other critical minerals, but targets are not set for them, and the RFI makes clear that REEs are the main objective.

Commercially valuable REEs include neodymium and praseodymium, which are used to make permanent magnets. Demand for those magnets is expected to skyrocket in concert with that for electric vehicles (EVs) and wind turbines. Other REEs, lanthanum and cerium, are used in petroleum-refining catalysts, automotive catalytic converters, and phosphors and as additives in glass for applications such as flat-panel displays, cell phone screens, and camera lenses.

Since 2014, DOE’s National Energy Technology Laboratory has been developing separation and extraction processes to recover REEs and other critical minerals from unconventional feedstocks in an economical, nonpolluting manner, says a spokesperson for DOE’s Office of Fossil Energy and Carbon Management. West Virginia University also conducts DOE-supported R&D in that area. One major source of coal waste is acid mine drainage, the acidic water that flows from the mining waste. This water leaches out REEs and other minerals, and research has shown that nearly all the REE content can be recovered in the process of remediating the water, the spokesperson says.

But Alex King, former director of the DOE-funded Critical Materials Institute at Ames Laboratory, says the huge volume of coal wastes that would have to be processed to separate meaningful quantities of REEs makes it unlikely that the process could be commercially viable. The wastes contain 200–400 ppm of REEs, he says, barely above the mean concentration in Earth’s upper crust. “You might be able to dig up some dirt from your backyard and get nearly as much rare earths,” he says.

King estimates that producing 10 000 tons of REEs annually from coal wastes—about one-quarter the output of the US’s sole REE mine, at Mountain Pass, California—would require two to three truckloads of coal waste per minute to be unloaded at a processing plant. A similar quantity of chemicals would need to be delivered. Processing wouldn’t appreciably reduce the amount of waste, he adds. “When you’ve extracted a few hundred parts per million out of a ton of rock, you’ve still got basically a ton of rock to dispose of.”

The DOE spokesperson acknowledges that the concentration of REEs in coal wastes is well below the tens of thousands of parts per million that are contained in bastnasite and monazite ores mined in the US and abroad. The bastnasite at Mountain Pass, for example, is one of the richest REE deposits in the world and contains REE concentrations of 8–12%.

For coal, the DOE spokesperson says, the main value proposition is that much of the work has already been done once the coal and mine tailings have been dug up. Easy recovery can be as important to the economic viability of the mining as the concentration of the metals of interest, the spokesperson adds. China, by far the world’s largest producer of REEs, extracts much of them in a relatively easy process from ion-adsorbed clays that have very low REE concentrations.

The RFI and other initiatives to spur domestic production of REEs and another critical element, lithium, were highlighted by President Biden at a 22 February White House event. Biden announced that the Defense Department will provide $35 million to MP Materials, owner of the Mountain Pass mine, to help build an REE processing and refining plant for heavy REEs such as dysprosium and terbium at the mine site. MP will spend $700 million by 2024 to refine REEs and fabricate magnet materials at a new plant in Fort Worth, Texas, CEO James Litinsky says. MP signed a long-term agreement in December to supply General Motors with manufactured rare-earth materials, alloy, and finished magnets for EV motors. As it develops those upstream capabilities, MP continues to ship REE concentrates from the mine to China for processing and manufacturing.

Biden also touted plans by Berkshire Hathaway Energy Renewables to extract lithium from the superheated brines it pumps from deep geological formations to produce geothermal energy. Located adjacent to the Salton Sea in California, the proposed project has received financial backing from the state, and Berkshire Hathaway is to break ground this spring on a facility designed to demonstrate the commercial viability of its extraction process. If successful, the company says it could begin commercial operations in 2026. At full scale, it says, it could produce 90 000 tons of lithium there annually. For comparison, total world production in 2021 was 100 000 tons, and US consumption of the light metal was 2000 tons, according to the US Geological Survey.

DOE is also distributing $3 billion that was included in the infrastructure act for refining EV battery materials such as lithium, cobalt, nickel, and graphite and for battery recycling facilities. One such recycling effort lauded by Biden comes from Redwood Materials, which in February began collecting and transporting end-of-life EV lithium-ion batteries in California for processing at its Nevada facility. King says that battery recycling is unlikely to become profitable until the supply of recycled material reaches about 10% of what is required for new EV production. Until then, significant incentives will be needed for recycling. King points to another problem facing prospective recyclers: Battery technology is changing so rapidly that recycling processes resulting in readily usable battery compounds today may become outmoded in a few years’ time.