Coal ash, red mud, and mine tailings are usually treated as major waste problems. Yet these enormous waste streams also contain valuable materials, including silica, rare earth elements, and other critical minerals. A research team led by Worcester Polytechnic Institute (WPI) has received a $3.3 million award from the National Science Foundation's Growing Convergence Research program to investigate whether biological strategies used by diatoms, sea sponges, and plants could help recover those resources with less energy and fewer harsh chemicals.
The five-year, two-phase effort is being led by Mingjiang Tao, associate professor in the WPI Department of Civil, Environmental, and Architectural Engineering. Professors Carrick Eggleston and Yan Wang are serving as co-principal investigators. Researchers from George Mason University, the University of California San Diego, the University of Massachusetts Amherst, and the University at Buffalo will also contribute.
"Recovering critical minerals is only part of the opportunity," Tao said. "We want to develop a process that uses as much of each waste stream as possible, separating strategically important elements while converting the remaining material into useful products. That whole-material approach could fundamentally change how industries manage waste and obtain essential resources." The project is designed to tackle two related problems.
Many silicon-derived materials used in concrete, glass, ceramics, semiconductors, and silicones require high temperatures, large amounts of energy, and intensive chemical processing to produce. At the same time, industry generates vast quantities of silicon-rich waste, including coal ash residue, red mud, mine tailings, concrete debris, waste glass, and metallurgical slag. Much of this material ends up in landfills, ponds, impoundments, and large waste piles, even though it can contain useful silicon, critical minerals, and rare earth elements (REE).
One estimate suggests that 11 million tons of REEs trapped in U.S. coal ash landfills is worth $8.4 billion -- nearly eight times the nation's current raw domestic reserves. Rare earth elements and other critical minerals are important for electronics, clean-energy technologies, transportation, and national security. Looking to Nature for a Cleaner Approach To find a better way to recover these materials, the researchers are turning to biology.
Diatoms, sea sponges, and certain plants use biological molecules and organic scaffolds to collect dissolved silicon and build complex silica structures under relatively mild conditions. The team hopes to adapt those natural processes to create lower-energy methods for breaking down silica-rich industrial waste. The goal is not only to release rare earth elements and other critical minerals trapped inside the material, but also to convert the silica itself into useful products.
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