Researchers from Wayne State University in Detroit are looking at how to harvest rare earth elements from coal fly ash. The project is being funded by a $540,000 grant from the U.S. Department of Energy, and WSU is working with researchers from the University of California, Los Angeles and the Los Alamos National Laboratory.
Rare earth elements are vital to technologies including consumer electronics, communications systems, renewable energy, and military hardware. China has controlled more than 90 percent of the rare earth elements market since the 1990s, and the U.S. continues to search for domestic supplies.
While not rare in terms of prevalence, the elements are not found in large concentrations and are difficult to separate and purify. There are various methods to extract the elements from coal and its byproducts, making use of the 1.5 billion tons of fly ash in landfills across the country.
The researchers have proposed a new process using alkaline hydrothermal leaching and a new sorbent material. The project involves dissolving the elements from fly ash to an aqueous solution and transferring the metals using a silica-based nanomaterial with element-specific binding sites.
“The main innovation in the project is to modify molecules currently used with MRI contrasting agents — chemicals a doctor injects into a patient so they can see certain organs on an MRI — so that we can get them to stick to a solid surface to separate rare earth elements,” says Timothy Dittrich, assistant professor of civil and environmental engineering at WSU and the project’s principal investigator.
The team is collecting fly ash from a Detroit power plant and has been running tests to establish ideal conditions and bonding systems for effective removal of the elements. The technique will be used to extract concentrated amounts of the elements for conversion to oxides and, eventually, refined metals.
“Using this separation technique will result in a solvent-free extraction process that is more environmentally benign than many liquid-liquid extractions that typically incorporate organic solvents,” says Dittrich.
The method is also less costly and labor intensive than its predecessors.