A report on the effects of coal ash listed its health effects. They include "several types of cancer, heart damage, lung and kidney disease, respiratory distress, reproductive problems, gastrointestinal illness, birth defects, impaired bone growth in children, nervous system impacts, cognitive deficits, developmental delays, and behavioral problems." Similarly, Jared Sullivan's 2024 book Valley So Low poignantly described the comprehensive human health and ecological risks of a dike failure and subsequent coal ash spillage into the Emory River channel, Roane County, Tennessee.
 
Interestingly, as smartphones, computers, and other electronic devices become ubiquitous, REE have become essential in the manufacturing and production of high-tech components. Exactly what rare metals are present in coal ash and in what quantity? Can coal ash be ‘mined’ for these highly sought resources?
 
To answer these questions, a group of scientists led by Drs. James C. Hower and John G. Groppo, in collaboration with scientists and engineers from Physical Sciences Inc., Winner Water Services, and Baylor University, have been using scanning electron microscopy, electron dispersive spectroscopy, and transmission electron microscopy to investigate the components of coal ash extracted from eastern Kentucky. Their decade-spanning scholarly work has been reported in the scientific literature. Their most recent study was published in the journal Minerals.
 
Their analysis found several minerals that can be processed to extract REE. Samples of coal ash contained zircon (ZrSiO₄) and baddeleyite (ZrO₂). Hafnium, another important element, chemically resembles zirconium and can also be found in the latter silicates. According to the U.S. Geological Survey, zirconium is used in nuclear fuel cladding, chemical piping in corrosive environments, heat exchangers, and various specialty alloys. Hafnium, on the other hand, is used in nuclear control rods, superalloys, nozzles for plasma arc metal cutting, electronics, and high-temperature ceramics.
 
Hower, Groppo, and their team also found fergusonite (YNbO₄), yttriaite (Y₂O₃), and xenotime (YPO₄), minerals that are sources of ytterbium. The Los Alamos National Laboratory reported that this REE has applications in refining and strengthening stainless steel, fiber optics, electronics, ceramics, and portable X-ray machines. Previous studies of the same fly had also identified monazite, a mineral that contained a broad range of REE. 
 
As noted by Hower, “Our recent papers highlight the scale of the extraction of metals from fly ash, while the fly ash particles average about 10 microns in diameter, the acids used in processing can only penetrate about 3 microns. Further, many of the minerals of interest are considerably smaller and are embedded within the alumino-silicate fly ash glass.”
 
At current REE prices, Hower noted that these metals, by themselves, may not provide enough of a return to justify the processing. Nevertheless, perfecting the extraction process is important and may lead to cost-effective future applications and, eventually, removing metals from eastern Kentucky coal-blend landfilled ash.

Dr. John Groppo (left) and the research team at the University of Kentucky's Center for Applied Energy Research receive fly ash for their investigation. The inset shows spherical fly ash particles at 2,000x magnification. Credit: Dr. James Hower (fly ash delivery); U.S. Department of Transportation/Wikimedia Commons (inset).