There are currently millions of tons of coal ash left over from burning the planet’s dirtiest fossil fuel that are sitting in ponds and landfills. They usually end up leaking into waterways and pollute soil. But this toxic waste may also be a treasure trove for the 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 — nearly eight times the amount the US has in domestic reserves — worth around US$ 8.4 billion, according to recent research led by the University of Texas at Austin.
It offers a huge potential source of domestic rare earth elements without the need for new mining, said Bridget Scanlon, a study author and research professor at UT’s Jackson School of Geosciences. "This really exemplifies the ‘trash to treasure’ mantra," she said. "We’re basically trying to close the cycle and use waste and recover resources in the waste."
These so-called rare earths are a cluster of metallic elements, with names like scandium, neodymium and yttrium, which exist in the Earth’s core. They have a critical role in clean technology, including electric vehicles, solar panels and wind turbines.
Despite their name, these metals are not rare in nature, but can be hard to extract and separate from the ore that surrounds them such that demand is outpacing supply.
As the world moves away from planet-heating fossil fuels, more rare earths will be needed. Demand for the metals is expected to soar up to seven times current levels by 2040, according to the International Energy Agency.
Yet US supply remains small. Its only large scale rare earths mine is Mountain Pass in California. The country currently imports more than 95 percent of its rare earth elements, the vast majority of which come from China, posing supply chain and security issues.
"We need to improve the situation," Scanlon told CNN. That’s why there has been a move to look at unconventional sources of rare earths, she said, "and one of these sources is coal and coal byproducts."
Coal ash contains relatively low concentrations of rare earth elements compared to what can be mined directly from underground deposits. The advantage is that it’s readily available. Around 70 million tons of coal ash is produced each year in the US.
"There’s huge volumes of this stuff all over the country. And the upfront process of extracting… is already taken care of for us," said Davin Bagdonas, a study co-author and research scientist at the University of Wyoming.