Scientists discover dozens of rare metals needed for clean energy hidden inside toxic coal waste

Millions of tons of coal ash left over from the burning of the world's fossil fuels sit in lakes and landfills, leaching into water and contaminating soil. But this toxic waste could also be a treasure trove of rare earth elements needed to propel the world toward clean energy.

Scientists analyzed coal ash from power plants across the United States and found it could contain up to 11 million tons of rare earth elements — about eight times the amount the U.S. has in domestic reserves — worth about $8.4 billion, according to a recent study led by the University of Texas at Austin.

It provides a large potential source of rare earth elements without the need for new mines, said Bridget Scanlon, study author and research professor at UT's Jackson School of Geosciences. “This is a true example of the 'waste to keep' mantra,” he said. “We're actually trying to close the loop and use the waste and get resources from the waste.”

The so-called rare earths are a group of metal elements, with names such as scandium, neodymium and yttrium, that exist in the center of the Earth. They play an important role in clean technology, including electric vehicles, solar panels and wind turbines.

Despite their names, these metals are not inherently rare, but they can be so difficult to extract and separate from the surrounding ore that demand outstrips supply.

As the world moves away from fossil fuels that heat the planet, rare earths will be needed. Demand for metals is expected to increase to seven times current levels by 2040, according to the International Energy Agency.

Yet the US supply remains small. Its only major rare earth mine is Mountain Pass in California. The country currently imports more than 95% of its rare earths, most of which come from China, posing supply chain and security issues.

“We need to improve the situation,” Scanlon told CNN. That is why there has been a movement to look for unusual sources of rare earths, he said, “and one of these sources is the production of coal and coal.”

Coal ash contains a relatively low concentration of rare earth elements compared to what can be mined directly from the ground. The advantage is that it is easily available. About 70 million tons of coal ash are produced each year in the US.

“There are a lot of these things all over the country. And the previous extraction process… is already taken care of for us,” said Davin Bagdonas, author and research scientist at the University of Wyoming.

Where the coal comes from determines how irregular the Earth's rare earth background is, the study found.

Coal ash from the Appalachian Basin contains very high amounts of rare earth elements, but only 30% can be extracted. Coal ash from the Powder River Basin, which straddles Wyoming and Montana, has a low average volume of material but more than 70% can be removed.

Coal ash disposal can be very expensive, said Paul Ziemkiewicz, director of the Water Research Institute at West Virginia University, who was not involved in the study. The cost of mining needs to be weighed against how much product can be recovered, he told CNN.

“Strong acids and bases are needed to extract rare earth elements. Both are expensive,” said Ziemkiewicz. Coal ash from the West can contain high concentrations of alkaline minerals, he added, which can increase costs as the alkalinity neutralizes the acid.

If more chemicals are needed in the process, there are potential environmental impacts.

Rare earth elements also make up a small portion of coal ash, Ziemkiewicz added, so their removal “will not change the volume that needs to be disposed of and stored.” Coal ash contains impurities such as mercury, arsenic and lead, making it a very dangerous stream.

The study's authors, however, suggest that the value of extracting rare earth metals could be used to offset the cost of improving the way coal ash is stored and managed.

In April, the Biden administration announced a $17.5 million investment in projects to rid the world of coal and its waste.

The funding will “increase our nation's security while helping rebuild America's manufacturing sector and revitalize energy and mining communities across the country,” Energy Secretary Jennifer Granholm said in a statement at the time.

Some have expressed concern that turning coal ash into something valuable could be used to fuel more coal, the dirtiest fuel that heats the planet.

It's not something Scanlon is too worried about. “We'll be using legacy waste for the most part,” Scalon said. There are currently more than two billion tons of coal ash stored across the US, according to the Department of Energy. “There is no indication that future reliance on coal ash as a feedstock source will promote coal-fired power,” a DOE spokesperson said.

The broader goal is to find ways to get a range of products from coal in addition to rare earths, Scanlon said, to extract value from it without burning it.

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