Unlocking value from silicon-rich waste with help from biology

Mine tailings and other silicon-rich wastes may look like materials with little value left. But locked within their tough mineral structures can be valuable elements and resources that are difficult-and often energy-intensive-to recover.

Mine tailings, one of the silicon-rich waste streams being considered in the project. Photo: U.S. Geological Survey, Public Domain.

As part of a newly funded National Science Foundation collaborative research project, George Mason University researchers are exploring whether nature can offer a different way to unlock those resources.

"Many of these materials still contain valuable resources, but they are locked inside very stable silicate structures," said Xijin (Emma) Zhang, an assistant professor in George Mason's Sid and Reva Dewberry Department of Civil, Environmental, and Infrastructure Engineering. "We would like to explore alternative and sustainable ways to break down these materials and recover what is valuable from them."

Silicon is the second most abundant element in Earth's crust and is a major component of minerals in rocks, mine tailings, concrete, and many industrial materials. Yet breaking down these stable silicate structures can require high temperatures, substantial energy, or highly corrosive chemicals. Zhang and her collaborators are investigating whether biological processes can accomplish some of these transformations under much milder conditions.

Xijin (Emma) Zhang. Photo provided.

The effort brings together researchers from five institutions, including George Mason, Worcester Polytechnic Institute, the University of Maryland, the University of California San Diego, and University of Massachusetts Amherst. By combining expertise in engineering, biology, geochemistry, and materials science, the researchers hope not only to develop new approaches for processing silicon-rich materials, but also to establish a new interdisciplinary field they call "Si-X TechnoBioGeoChemistry."

At George Mason, Zhang is working with Monique Van Hoek, a professor in the School of Systems Biology in the College of Science, to explore how microorganisms and the molecules they produce interact with silicate minerals. The collaboration brings together biological and engineering perspectives to better understand how natural processes can be harnessed to transform materials that are otherwise difficult to break down.

Monique Van Hoek. Photo: Creative Services, Office of University Branding.

The project builds on Zhang's years of research in biomineralization. After studying calcium-based biomineralization during her PhD work, Zhang expanded her work to silicon-rich materials while continuing to explore how biological systems can reshape materials in sustainable ways.

The researchers are especially interested in waste streams such as mining residues, demolished concrete, and industrial byproducts. Rather than viewing these materials simply as waste to be managed, the team sees them as potential resources. According to Zhang, these materials often contain valuable elements trapped within strong silicate matrices, while the silicon-rich material itself may also have potential for reuse.

"We can turn these waste resources into useful material, and that can first create new value, and second, reduce some waste and reduce some management cost associated with the waste," she said.

Zhang's lab is developing bio-enabled methods to break down and transform silicate materials under mild conditions. They are investigating how microorganisms, biological molecules, and other nature-inspired processes can replace or complement conventional approaches that rely on extreme temperatures and harsh chemicals.

"We're focusing on how to use sustainable and bio-enabled pathways to break these waste materials down in a low-energy and low carbon-emission way," Zhang said. "At the same time, we want to understand how we can release valuable components and make the remaining materials useful again."

Silica-based skeletons in glass sponges. Photo: Randolph Femmer/USGS, Public Domain.

The approach could open new pathways for using resources recovered from silicon-rich waste. Silicon-containing materials produced through these processes could potentially be reused in a wide range of applications, including new cement and concrete materials, glass products, electronic technologies, while valuable elements released from the silicate matrix could contribute to the recovery of critical minerals. During the initial two-year phase, researchers will investigate the fundamental biological, chemical, and geological processes that control these transformations and evaluate the feasibility of the overall approach. Those findings will help the team identify the most promising directions for future development.

Beyond the scientific advances, the initiative will provide interdisciplinary training opportunities for graduate students and researchers working across traditional disciplinary boundaries. By bringing together biology, geology, and engineering, Zhang and her collaborators aim to rethink how society extracts value from secondary resources and how materials now considered waste might become resources for the next generation of technologies.