Residual materials from combusted fossil fuels may hold a significant concentration of rare-earth elements, representing a substantial economic asset potentially valued in the billions of dollars.
A 2024 academic publication by geologists has projected that the waste ash originating from coal combustion in fossil fuel power stations could contain rare earth elements to the tune of approximately US$165 billion, with an estimated $97 billion of this amount being amenable to feasible extraction.
Efforts focused on the recovery of these valuable elements, as spearheaded by a research contingent from the University of Texas at Austin, could furnish the United States with a domestic supply of these indispensable materials. This approach would circumvent the arduous processes of conventional mining and alleviate reliance on international imports, from which the nation currently procures the majority of its rare-earth resources.
“This initiative truly embodies the principle of transforming waste into valuable assets,” stated Bridget Scanlon, a geologist affiliated with the Jackson School of Geosciences. “Our objective is to complete the resource cycle by repurposing waste materials and extracting valuable components, concurrently mitigating adverse environmental consequences.”
Rare earth elements (REEs) encompass a collection of 17 metallic elements, comprising the 15 lanthanides found on the periodic table, in addition to yttrium and scandium. These substances are designated as “critical minerals” within the United States, playing an indispensable role in a multitude of industries and technological advancements, including the manufacturing of batteries, wind turbines, electric vehicles, and sophisticated electronic devices such as smartphones.
The United States possesses limited domestic reserves of REEs. Consequently, the nation is almost entirely dependent on imported sources, with a predominant proportion—approximating 70 percent—originating from China.
However, recent scholarly investigations propose that a substantial, yet overlooked, reservoir of REEs may be readily available: the 52 billion tons of coal-ash waste generated by power plants across the US since the mid-20th century.
The underlying mechanism is as follows: Coal, which is essentially ancient, fossilized plant matter, is not a pure substance. Instead, it incorporates minute quantities of other geological materials during its formation and consolidation over vast geological timescales. These trace constituents are present in such negligible amounts that their extraction is not economically viable; they certainly do not enhance the value of coal as a fossil fuel resource.
An intriguing transformation occurs when coal is subjected to combustion. The volatile components of coal, such as carbon, hydrogen, and sulfur, are released as gaseous byproducts, leaving behind the non-combustible inorganic residues. This residue includes clay minerals, quartz, and crucially, REEs.
Given that a significant portion of coal’s mass is dissipated as flue gas, the concentration of REEs within the residual glassy ash is elevated by a factor of four to tenfold when compared to unburnt coal.
It is important to note that these concentrations are considerably lower than those found in commercially mined ores. Nevertheless, the processing of coal ash does not necessitate novel extractive mining operations; it involves materials that have already been excavated. Therefore, it presents a potentially worthwhile undertaking.
Under the co-leadership of Scanlon and geologist Robert Reedy, the research team meticulously compiled extensive data spanning decades, covering aspects of ash composition, extraction efficiencies, and the geographical distribution of waste storage sites throughout the United States. Their projections indicate that approximately 11 million tons of REEs could be present in accessible coal-ash deposits dating from 1985 to 2021—a quantity nearly eight times greater than the current estimated US reserves.
The total theoretical monetary value of the 15 lanthanide REEs contained within all US coal ash reserves is estimated at approximately $56 billion. Depending on the specific location, between 30% and 70% of this coal ash is considered accessible, which consequently reduces the projected total value of accessible ash to $14 billion.
The lanthanides that can be practically recovered from this accessible coal ash are calculated by the researchers to be worth as much as $8.4 billion.
However, when the inclusion of yttrium and scandium is considered, these financial figures escalate dramatically, reaching a total aggregate valuation of $165 billion. Of this substantial sum, an estimated $97 billion is deemed recoverable, according to the findings presented in the study.
It is important to acknowledge that these estimations are largely theoretical, as the sophisticated extraction methodologies are still undergoing comprehensive investigation. Despite this, the potential economic and strategic significance of this resource is substantial enough to warrant serious consideration by both scientific bodies and governmental agencies in the United States, who are actively exploring these possibilities.
“Beyond bolstering the energy security of the United States through the development of domestic REE resources, the economic benefits derived from the production of these rare earth elements could significantly offset the expenditures associated with the remediation of unlined ash landfills or ponds situated in environmentally sensitive regions,” the research team concluded.
“The potential for REE resource development utilizing coal ash deserves thorough evaluation on a global scale, particularly in nations where coal ash is a readily available byproduct.”
Numerous alternative pathways for the potential sourcing of rare earth elements exist; however, many of these may also present considerable challenges in terms of extraction feasibility.
In recent years, scientific inquiry has indicated that volcanic formations could represent a promising source of these valuable minerals.
“Extinct volcanoes rich in iron are frequently exploited for iron ore extraction,” explained Michael Anenburg, a geologist from the Australian National University, in an article for The Conversation. “Our findings suggest that existing mining operations at such sites could potentially be adapted to yield rare earths as well.”
Another avenue of exploration involves plant life. In research that was recently published this month, scientists identified a fern species possessing a remarkable capability: it can absorb and accumulate rare earth elements from metalliferous soils, effectively performing a natural extraction process from the ground.
“Rare earth elements are indispensable metallic components for clean energy technologies and advanced applications; however, their supply chain is currently constrained by environmental and geopolitical complexities,” articulated Liuqing He, a geoscientist with the Chinese Academy of Sciences, along with his colleagues in their published paper. “Phytomining, which represents a sustainable approach employing hyperaccumulator plants for metal extraction from soil, offers a promising strategy for the future supply of REEs but remains an area requiring further in-depth exploration.”
As research continues to unveil these promising opportunities, there is no question that the global approach to the extraction of these highly valuable elements will have profound implications.
The comprehensive study on coal-ash rare earth elements was published in November 2024 in the esteemed International Journal of Coal Science & Technology.
