Coal Ash, It Turns Out, Is A Potentially Huge Source of Rare Earth Elements Needed for a Multitude of Products

Rare earth elements are used to produce LED screens, fluorescent lighting, magnets, batteries, radar systems, lasers, high-temperature ceramics, shielding in nuclear reactors, MRI scanning, lasers, catalytic converters, camera lenses, aluminum alloys for lightweight aircraft and sports equipment, and much more. They are extremely valuable and we import most of them from places such as China, which is hardly a good situation. But, there is an at-home source that offers a big-time environmental clean-up benefit. It is coal ash, of all things.

Photomicrograph made with a scanning electron microscope and back-scatter detector: cross section of fly ash particles, by WABeggs

A study published last September and titled “Coal Ash Resources and Potential for Rare Earth Element Production in the United States,” provides the details and here are some excerpts: (emphasis added)

Rare earth elements (REEs) are critical for many industries, including solar panels, permanent magnets for wind turbines, electric vehicles, and batteries, making them essential for national security and economic prosperity. All 18 REEs (16 in lanthanide series + yttrium + scandium, REEYSc) are included in the list of critical minerals by the USGS (Federal Register 2022).

The US is heavily reliant on imports of REES from China, increasing the vulnerability of the supply chain. The US Department of Energy (DOE) estimates that current conventional US REEs reserves total 1.4 million tons (Mt); however, unconventional coal sources could provide an additional 11 Mt of REEs (US 2020).

The US DOE developed the Carbon Ore, Rare Earth and Critical Minerals (CORE-CM) program to assess the value of US coals and associated byproducts as feedstocks for domestic production of REEs and critical minerals to enhance national and economic security (US DOE, 2021). In addition, coal ash generated from coal combustion in power plants is environmentally sensitive.

Coal ash or coal combustion byproducts contain contaminants, such as Hg, Cd, As, and radionuclides, having the potential to contaminate water sources if not properly managed (Zielinski and Finkelman 1997). Therefore, extraction of REEs from coal ash could be used to offset costs of improving management of coal ash impoundments to reduce adverse environmental impacts.

Previous studies indicate that REEs are concentrated by factors of 4–10 times in coal ash from power plants because they are non-volatile and accumulate in the ash during combustion (Franus et al. 2015; Kolker et al. 2023; Scott and Kolker 2019).

Therefore, coal ash could serve as a viable resource for REEs (and potentially other critical minerals).

A reconnaissance analysis of REEYSc levels in 100 ash samples throughout the US reveals that mean total REEs + Y + Sc is higher for Appalachian coals (591 mg/kg) relative to Illinois coals (403 mg/kg) and Powder River Basin coals (227 mg/kg) (Taggart et al. 2016).

Ashes from the different coal basins have different REE signatures (Hower et al. 2021). REE speciation and modes of occurrence in coal ash are also important and affect extractability of REEs from coal ash (Fu et al. 2022; Liu et al. 2019; Pan et al. 2018).

The disposition of coal combustion products includes onsite use and sales to produce aggregate, cement, road building materials, and gypsum. The remaining byproducts are generally disposed of in landfills or ponds. If a power plant is located adjacent to a mine, particularly a surface mine, often termed “mine-mouth” power plant, products may be used for back-fill in mined areas…

Rising interest in developing sources of REEs within the US to enhance security has resulted in increasing focus in evaluating coal and coal combustion products as potential sources of REEs.

This study focused on spatiotemporal variability in coal ash generated at power plants as a source of REEs. Coal production doubled from 1950s (0.45 Gt/yr) to late 2000s (1.04 Gt/yr) but reduced to half within the past decade (0.52 Gt 2021). Most (79%) of the US coal consumption has been for power generation (1950–2021). Coal accounted for about 50% of power generation from 1950 to 2005 but decreased to 20% by 2021.

A total of 52 Gt of coal was produced (1950–2021) and associated ash represents about 10% of coal production (5.8 Gt). Burning coal in power plants concentrates REEs by factors of 4 to 10, enhancing the value of ash as a source of REEs. An estimated 69% of ash is considered potentially recoverable (1985–2021) as it was stored in landfills and ponds on and offsite whereas the remaining 31% was sold and used by other industries.

The Powder River Basin in Wyoming accounted for about 44% of US coal production and almost 27% of associated ash since 2000. Most coal that is produced from a specific basin is also consumed within that region with the major exception of the Powder River Basin which exports most of its coal to other states.

Using mean REE concentrations in coal ash derived from major coal basins (Appalachian, Illinois, and Powder River Basin, 85% of US production 1950–2021), the potentially recoverable ash content (68% of total), varying extraction rates (30% for Appalachian and Illinois basins and 70% for Powder River Basin), and 2020 REO market prices resulted in an estimated potential value of REEs in ash of about $8.4 billion.

Including yttrium and scandium increases the estimated value to $97 billion. In addition to enhancing energy security in the US through development of REE resources, the economic value of producing these REEs could help offset the costs of remediation of unlined ash landfills or ponds in environmentally vulnerable areas.

So, what we learn is that coal use has a substantial side benefit. The same may be said of natural gas, as frack water often contains lithium that can be recovered. Fossil fuels generate the rare earth elements we need for so much else. Nice to know!

#Coal #CoalAsh #RareEarthElements #REEs #FossilFuels #NaturalGas

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