A Worcester Polytechnic Institute-led research team is combining biology, artificial intelligence and materials science to investigate whether rare earth elements and other critical minerals trapped in industrial waste can become a useful secondary resource.
Coal ash has long created a waste-management challenge for the power industry.
Researchers now see another possibility. Some coal ash could provide a secondary source of rare earth elements (REEs) and other critical minerals.
A 2024 study estimated that potentially accessible and extractable rare-earth oxides in U.S. coal ash carried an estimated 2020 value of about $8.4 billion. The researchers examined ash associated with the Appalachian, Illinois and Powder River coal basins and applied assumed extraction efficiencies and 2020 rare-earth oxide prices.
The figure does not represent a proven reserve or the current market value of recoverable material.
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It represents a modelled resource-value estimate based on specific technical and price assumptions.
That distinction matters.
Coal ash may contain significant quantities of rare earths. However, companies still need to solve a much harder problem: recovering those elements at sufficient scale, purity and cost to create a commercially useful supply.
A new research programme at Worcester Polytechnic Institute (WPI) is approaching that challenge from an unusual direction: nature.
The five-year, two-phase project has received a $3.3 million award from the U.S. National Science Foundation’s Growing Convergence Research programme. Researchers are studying how diatoms, sea sponges and plants create complex silicon structures under relatively mild conditions.
They want to understand whether those biological mechanisms can help engineers develop new ways to process industrial waste.
The $8.4 Billion Estimate Needs Context
The $8.4 billion figure comes from a study published in the International Journal of Coal Science & Technology.
The researchers examined coal ash associated with three major U.S. coal-producing regions: the Appalachian, Illinois and Powder River basins.
They estimated rare-earth oxide concentrations in the ash and assessed how much material could potentially come from landfills, ponds and other storage sites. They then applied assumed extraction efficiencies and 2020 rare-earth oxide prices.
Those calculations produced an estimated $8.4 billion in 2020 rare-earth oxide value for the potentially accessible and extractable ash considered in the study.
The researchers did not assume that every tonne of U.S. coal ash offered the same level of access or recoverability.
That makes the distinction between resource potential and recoverable supply critical.
A company cannot simply excavate coal ash, separate the rare earths and sell them.
The elements often occur within complex mineral phases. Processing must first liberate them from those phases before separation and purification can begin.
The Mineral Is There. Extraction Is the Problem.
Coal combustion can concentrate rare earth elements in ash. However, the combustion process does not automatically make those elements easy to recover.
USGS research has found rare earths in coal ash within complex mineral matrices. Those mineral associations can create significant processing challenges.
A commercial operation would need to perform several tasks successfully.
It would need to concentrate the rare earths, liberate them from their host minerals, separate individual elements and produce products at commercially useful purity.
Every stage can add cost.
The concentration of rare earths alone therefore cannot determine whether recovery makes economic sense.
Operators would also need to manage reagent consumption, energy demand, impurity control, separation efficiency and residual waste.
That explains why a large theoretical resource does not automatically create a viable mining or processing business.
A 2026 USGS Study Shows the Economic Gap
A separate 2026 USGS assessment of coal and coal ash in the U.S. Gulf Coast illustrates the challenge.
Researchers analysed 118 samples from outcrops and 14 mines. Their tests showed that rare-earth extractability from coal ash generally reached 5% or less with the weak acid they tested, even though the ash contained elevated rare-earth concentrations compared with the original coal.
The researchers also modelled the potential economic value of the ash.
For the Gulf Coast material they examined, the study estimated a median basket value of about $4.40 per tonne of ash, assuming roughly 30% extractability.
The researchers applied that estimate to about 258 million tonnes of ash and calculated a modelled value of approximately $1.2 billion.
The figure does not establish commercial viability.
Instead, the USGS analysis points to another part of the economic equation. Recovery may require valuable co-products, such as activated carbon or humic acids, along with potential savings from reducing ash-disposal and remediation costs.
That provides an important counterpoint to the $8.4 billion national estimate.
The critical question is not simply how much rare earth a waste stream contains.
It is how much value an operator can recover from each tonne after processing costs.
WPI Is Taking a Different Approach
The WPI project does not simply repeat conventional leaching research.
Instead, researchers are examining biological mechanisms that diatoms, sea sponges and plants use to build complex silicon structures under relatively mild natural conditions.
The team wants to understand those mechanisms at the molecular level. It will then investigate whether engineers can adapt those principles to silicon-rich industrial waste.
If the approach works, it could eventually reduce the energy and chemical intensity of some extraction processes.
However, the project has a broader goal than rare-earth recovery alone.
WPI says the team wants to develop methods that recover critical minerals while also producing valuable silicon-based materials from industrial waste.
The research will examine materials such as coal ash residue, red mud and mine tailings.
That whole-material approach could matter to the economics.
If rare-earth recovery alone cannot generate enough value to justify processing, additional products could improve the economics of the same waste stream.
AI Enters the Mineral-Processing Problem
Artificial intelligence forms another part of the WPI research programme.
The multidisciplinary team will combine bioengineering, geochemistry, materials science, computational modelling and AI to study how specialised biomolecules interact with silicon-rich waste.
Computational tools could help researchers identify promising molecular structures and reaction pathways before they conduct laboratory experiments.
That could reduce the number of experimental combinations the team needs to test.
But AI does not make the extraction technology commercially proven.
The researchers still need to demonstrate that the biological mechanisms work consistently with real industrial feedstocks.
For mining and mineral processing, however, the approach could have broader significance.
A successful platform could potentially support the processing of other complex waste streams where conventional methods struggle with low concentrations or difficult mineral chemistry.
Coal Ash Is Only One Potential Feedstock
The WPI programme targets several industrial waste streams.
Alongside coal ash, researchers are examining red mud, mine tailings and other silicon-rich wastes.
The project also aims to recover useful materials from the silica component instead of treating it solely as another residue.
That gives the research relevance beyond the coal industry.
Mine tailings provide another important opportunity.
Tailings can contain minerals that companies could not economically recover when they developed the original mine. Commodity prices, processing technology and environmental requirements can change that calculation over time.
A technology that can recover several products from the same waste stream could therefore create a different economic model from conventional single-commodity mining.
But researchers still need to prove that model in practice.
The Opportunity Is Secondary Supply, Not a Replacement for Mining
The attraction of coal ash and other industrial residues is straightforward.
The material has already gone through mining, transportation and processing.
If companies can recover valuable minerals from the remaining waste at competitive costs, they could potentially create additional supply without developing an entirely new mine.
Mineral recovery could also help offset waste-management or remediation costs in some cases.
That does not mean secondary resources will replace conventional rare-earth mining.
Instead, waste-derived materials could eventually complement primary production if recovery technologies achieve reliable performance and competitive economics.
Recent USGS work highlights the scale of the wider resource question. A separate August 2026 USGS assessment estimated about 83 billion metric tonnes of remaining coal resources in the upper 90 metres of the Gulf Coast region.
However, the assessment also noted the need for additional work to determine how much of the associated rare earth and critical-mineral content companies could actually extract.
That distinction runs through the entire coal-ash opportunity.
Geological abundance does not equal recoverable supply.
The Real Test Is Economics
For WPI’s approach to move from laboratory research toward commercial mineral processing, researchers must overcome several hurdles.
The technology must demonstrate consistent recovery across different waste streams.
It must control reagent and energy consumption.
It must achieve useful separation efficiencies.
And it must produce saleable materials at a scale that makes the processing chain economical.
The full chain matters:
waste collection → feed preparation → mineral liberation → extraction → separation → purification → product recovery.
Every stage affects the final economics.
Multiple products could improve the value of the feedstock. Remediation savings could provide another economic benefit.
But the WPI project has not yet demonstrated those commercial outcomes.
The research therefore represents an attempt to solve a difficult secondary-resource processing problem, rather than proof that a new commercial rare-earth supply source has already emerged.
From Waste Liability to Mineral Resource
The significance of the WPI programme lies in the question it asks.
Instead of searching only for new rare-earth deposits, researchers are investigating whether some of the materials needed for future critical-mineral supply chains already exist in industrial waste.
The $8.4 billion estimate illustrates the potential scale under a specific set of assumptions.
The $4.40-per-tonne Gulf Coast estimate illustrates how quickly that apparent value can change when researchers account for recovery rates and processing economics.
WPI’s research sits between those two realities.
The project is testing whether biology, AI and materials science can make difficult waste streams more valuable while reducing energy and chemical requirements.
If the approach eventually proves technically and economically viable, coal ash, mine tailings and other industrial residues could contribute to a broader secondary supply chain for rare earths and other critical minerals.
For now, the key question is not simply how many rare earths sit in U.S. coal ash.
The real question is how much companies can recover, at what cost, with how many products, and with what environmental benefit.
