Billions of dollars in rare earth elements may be hiding in America’s coal ash

An estimated 11 million tons of rare earth elements are sitting unused in coal ash landfills across the United States, worth roughly $8.4 billion at current prices, according to a research team at Worcester Polytechnic Institute that just won federal funding to try to extract them. The National Science Foundation awarded the WPI-led group $3.3 million through its Growing Convergence Research program to spend the next five years developing ways to pull those elements out using biology-inspired methods rather than the energy-intensive processes mining companies use today.

The $8.4 billion figure is not a small number set against how little rare earth material the country currently has on hand. Researchers say it amounts to nearly eight times the nation’s existing raw domestic reserves, all of it locked inside a waste product that power plants have spent decades burying rather than mining.

A five-year hunt led by a highway engineer

Mingjiang Tao, an associate professor in WPI’s Department of Civil, Environmental, and Architectural Engineering, is the lead principal investigator on the project, working alongside civil engineering professor Carrick Eggleston and mechanical engineering professor Yan Wang. Tao’s own research background is in sustainable highway infrastructure, including using fly ash and rice husk ash to make greener alternatives to Portland cement, according to his WPI faculty page, which makes coal ash’s waste-to-resource potential familiar territory even before this specific grant.

“Recovering critical minerals is only part of the opportunity,” Tao said, describing a broader ambition for the project than rare earths alone, according to the team’s own announcement of the award. His team wants to build a process that uses as much of each waste stream as possible, rather than treating rare earth extraction as an isolated chemistry problem bolted onto an existing landfill.

Borrowing tricks from diatoms and sea sponges

The five-year, two-phase project does not stop at coal ash. Tao’s team is also targeting red mud, a caustic byproduct of aluminum refining, and mine tailings left over from other extraction operations, treating all three as different flavors of the same underlying problem: valuable elements trapped in industrial leftovers that current processing methods cannot economically reach.

Their proposed solution borrows from biology rather than brute-force chemistry. Diatoms, sea sponges and certain plants all have natural mechanisms for collecting dissolved silicon from their environment at room temperature, and the WPI-led team is studying those mechanisms to design lower-energy methods for pulling rare earths free and converting the leftover silica into something usable, rather than discarding it as more waste.

That approach stands in contrast to how silicon-derived materials are typically produced now, a process that the research team’s own description characterizes as requiring high temperatures, heavy energy use and intensive chemical processing at every stage.

How much coal ash the country is sitting on

Coal ash is not a niche waste stream. The Environmental Protection Agency has estimated the country generated close to 130 million tons of it in a single recent year, some of it recycled into concrete and wallboard, and the rest disposed of in surface impoundments, landfills or, in some cases, discharged into waterways under permit, according to the agency’s own basics page on coal combustion residuals. The EPA regulates the material in part because it can carry mercury, cadmium and arsenic, contaminants that have nothing to do with the rare earths researchers now want to extract from the same landfills.

Four other universities are working alongside WPI on the grant: George Mason University, the University of California San Diego, the University of Massachusetts Amherst and the University at Buffalo. The NSF’s Growing Convergence Research program, which funded the effort, requires researchers to work across traditional disciplinary boundaries rather than inside a single department, according to the program’s own description of what the funding line is designed to do. The theory is straightforward: a chemist, a civil engineer and a materials scientist working separately on coal ash would each miss a piece of the problem that only shows up when the fields collide.

None of the five partner schools has previously led a project quite this broad on rare earth recovery. Coal ash, red mud and mine tailings are usually studied by separate research communities that rarely compare notes, since a mining engineer working on tailings and a highway engineer working on fly ash tend to publish in different journals and attend different conferences.

The separation between research communities is itself part of the reason the resource has stayed untouched for so long. Extracting rare earths from ordinary ore is already expensive; doing it from a waste stream that was never designed to be mined again adds a second layer of technical and regulatory difficulty that no single lab has had the funding or the mandate to tackle alone until now.

Whether an $8.4 billion resource actually gets extracted at any meaningful scale depends on questions this award does not answer by itself: whether a biology-inspired process can be run cheaply enough per ton to compete with imported rare earths, and whether utilities holding decades of buried ash are willing to let researchers, and eventually companies, dig back into it.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.