Coal ash, the waste left after burning coal, has long been regarded as an environmental nuisance. Yet a team of geoscientists, led by Bridget Scanlon, suggests that the mineral-rich residue may contain valuable rare earth elements (REEs).
In a recent study, the team estimated that up to $97 billion worth of these elements could be feasibly extracted from coal ash produced between 1985 and 2021. The findings could revolutionize how the US sources REEs, offering a domestic solution to a problem that has long been associated with geopolitical risks and environmental challenges.
The Critical Importance of Rare Earth Elements
Rare earth elements are a group of 17 elements essential to modern technology. These minerals, which include the lanthanides, yttrium, and scandium, play a pivotal role in the production of batteries, electric cars, wind turbines, and consumer electronics.
Due to their importance, the US has classified them as “critical minerals.” However, unlike other critical materials like oil or natural gas, the US is heavily reliant on imports of rare earth elements, with approximately 70% of its supply coming from China, which controls much of the global market.
The scarcity of domestic REE reserves in the US has led to concerns about both economic security and environmental sustainability. Mining and processing REEs are not only resource-intensive but also have significant environmental impacts.
As a result, scientists have been searching for alternative sources of these elements. According to researchers, coal ash could be a hidden treasure trove of rare earths, offering a less harmful method of extraction compared to traditional mining.
Unlocking the Potential of Coal Ash
When coal is burned for energy, its combustible materials like carbon and sulfur burn away, leaving behind a residue known as coal ash. Though the ash was once considered a waste product with little value, recent studies show that it contains significantly higher concentrations of REEs than unburnt coal. According to the University of Texas team, coal ash could hold between four to ten times more REEs than the coal it was derived from, making it an attractive target for recovery.
The researchers compiled decades of data on the composition of coal ash and the potential efficiency of extraction methods. They found that approximately 11 million tons of rare earth elements could be contained in accessible coal-ash deposits across the US. While the concentrations are still low compared to traditional ores, the fact that the material has already been extracted and is simply waiting for recovery makes the process far less invasive than traditional mining.
A Multi-Billion-Dollar Opportunity
The economic value of the rare earth elements within US coal ash is estimated at around $56 billion, based on the 15 lanthanides alone. When factoring in yttrium and scandium, this value jumps to an estimated $165 billion, with a recoverable portion of $97 billion.
These findings are based on theoretical calculations and assume that extraction methods can be developed to make the process viable. According to the researchers, the development of REE extraction technology could provide an economic boon while simultaneously addressing the environmental problems posed by unlined coal ash landfills and ponds.
Although this is a promising start, experts caution that the extraction of REEs from coal ash is still in its early stages. Methods to recover these elements are still under investigation, and the process would need to be scaled up to be commercially viable. Nevertheless, the researchers note that this could offer a much-needed alternative to the extraction of REEs from foreign sources, particularly China.
Expanding the Search for Rare Earths
While coal ash offers an exciting opportunity for REE recovery, it’s far from the only potential source. Over the years, scientists have proposed other unconventional methods for sourcing these critical minerals. For example, recent studies have suggested that volcanic deposits, particularly in extinct iron-rich volcanoes, could be tapped for rare earths. Likewise, researchers have explored the idea of phytomining—using plants to naturally absorb rare earth elements from soil.
In addition to these approaches, the coal ash research highlights the potential for sustainable methods to extract critical minerals from waste products. According to the researchers, this could pave the way for a cleaner, more sustainable future by turning waste materials into valuable resources. However, it remains to be seen whether these alternative sources will be able to meet the growing demand for rare earth elements in the coming decades.
