Coal Ash Could Supply Rare Earth Elements From Fossil-Fuel Waste

Modern life depends on metals.

The technologies, industries and infrastructure that define the present day would be impossible without 17 valuable metals called rare earth elements (REEs). They are used in computers, aircraft, cars and numerous other products.

Despite the name, REEs are not especially scarce. The challenge is that recovering them in useful forms is costly and technically difficult.

Scientists are increasingly finding that waste heaps produced by used fossil fuels hold substantial quantities of REEs, potentially providing a domestic supply of these metals.

REE deposits are not spread evenly around the planet. Mines in China produce roughly 70 percent of REEs and handle about 90 percent of the world's heavy rare earth processing, giving the country a monopoly.

These elements are essential to the clean-energy transition, with uses in solar panels, batteries and wind-turbine motors, alongside medical and defence technologies. An F-35 fighter jet, for instance, contains about 400 kilograms (900 pounds) of REEs.

For many nations, building an independent REE supply chain is viewed as crucial for national security, technological sustainability, economic stability and energy independence. It could also support a more circular materials economy.

Fortunately, considerable quantities of REEs seem to be simply 'sitting around', trapped within waste from spent fossil fuels.

Coal ash could provide rare earth elements

A 2024 study led by geoscientists at the University of Texas at Austin estimated that coal ash from US coal-fired power stations could contain nearly US$100 billion worth of REEs that can feasibly be extracted.

At present, Chinese imports account for approximately 70 percent of the US REE supply. The country has just one major working REE mine, in California. Although it supplies 16 percent of the world's rare earths, the US does not have domestic processing capacity.

The powdery coal ash is, intriguingly, a possible resource powerhouse. It is a by-product of burning coal, which itself was formed as extreme heat and pressure compressed the remains of ancient plants within Earth over hundreds of millions of years.

After most of coal's mass and burnable components have been consumed, the REE levels in the remaining ash can be up to 10 times greater than they were in unburned coal. This makes it an already-excavated source of critical materials.

The estimated 11 million US tons of REEs held in accessible coal ash is almost eight times larger than the amount contained in US domestic reserves.

As a result, countries are now competing to create viable extraction techniques.

Rare earth element extraction from fossil-fuel waste

At Australia's Monash University, engineers are applying environmentally benign acids to draw REEs from coal ash. In pilot demonstrations, they reported a 90 percent recovery rate across all 17 elements.

"The significance of this work lies in its dual impact: reducing environmental waste while securing domestic supply of critical minerals," explains Monash chemical engineer Sankar Bhattacharya.

The approach may also have wider applications. If it can be scaled up and commercialised, the Monash team says the process could treat other widespread waste streams, including electronic waste and tailings - the material left behind after valuable metals are extracted from mined ore.

"We don't have to dig up new mines. We can use something that's already processed and just sitting in landfill," Bennet Thomas, a sustainable resource recovery engineer at Monash, told AAP, adding that greater REE self-reliance can therefore tackle a "national risk".

Research published in the Journal of Environmental Management in 2025 likewise underlines coal ash's unused potential.

Engineers Ruchi Agrawal and Arthur Ragauskas estimated that coal ash worldwide could produce more than 300,000 US tons (272,000 metric tons) of REEs annually, "far exceeding global demand".

However, standard extraction processes come with significant disadvantages, such as poor recovery rates and toxic waste created after processing.

Researchers at Northeastern University are addressing this issue by pretreating coal tailings, increasing the yields of conventional extraction techniques three-fold.

Limits and alternatives for recovering REEs

Scientists are also investigating further approaches.

These include 'green' leaching solutions that use substances such as acids, electrochemical extraction, and nature-based methods involving metabolites produced by microbes that precipitate REEs from waste in an environmentally friendly way.

Phytomining is another possibility. It could employ "hyperaccumulator plants" that concentrate REEs in their tissues, making use of these natural marvels - because, apart from sequestering carbon, generating oxygen, purifying the air, cooling cities, making the world more beautiful, and supplying food and building materials, what have plants done for us lately?

Every technique has advantages and disadvantages, mainly involving environmental sustainability, resource needs, scalability and complexity.

Extraction methods will have to find the right balance, delivering high-quality REEs through processes that are both cost-effective and energy-efficient.

Whether any of these approaches can succeed at commercial scale remains to be seen.

The research appeared in the Journal of Coal Science & Technology and the Journal of Environmental Management.

This article was fact-checked by Clare Watson and edited by Clare Watson. Although we take pride in our process, we are only human. If you notice an error, please let us know.