Few people think of coal when they think of high-tech devices. However, that may soon change as researchers at the U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (NETL) work to recover materials called rare earth elements (REEs) from coal and coal-based materials.
REEs are essential to the manufacturing of many of the devices that people use every day. For instance, their unusual properties help make the best, strongest and lightest magnets in the world that are used in products from earbuds to electric motors that power car windows and mirrors. They also enhance light emissions, making them integral in fluorescent lighting, catalysts, computer screens and smartphones. In addition, rare earths are important in making nearly every technology used in defense systems that protect the country (see infographic for more uses).
Generally, all rare earths are important. However, DOE-NETL is focused on separating and extracting the heavier REEs like europium, gadolinium, terbium and dysprosium, as they are prevalent in coal but are less prevalent in nature. The heavy rare earths are less abundant than the lighter lanthanides and are typically more valuable.
Producing REEs domestically is important because the United States currently imports nearly all its rare earths supply from other countries, making it vulnerable to unpredictable shifts in the overseas markets. Traditionally, rare earths have been mined from other mineral ores, then refined and separated. However, researchers at NETL and external stakeholders have been working to prove that REE extraction from coal and coal-based products can be economically viable, providing a domestic source of these valuable materials.
Currently, rare earths are commercially produced from ores containing monazite (rare earth phosphate mineral) or bastnäsite (rare earth carbonate-fluoride mineral), as well as from ion-exchangeable clays, but NETL researchers are now turning to coal as a source of REEs. Every element contained in the Earth’s crust is present in coal. Rare earths are found in coal, coal mining byproducts such as the strata above and below coal seams, and coal preparation (coal washing) residues, making every step in the coal mining process a potential source of REEs.
Most of the common inorganic lanthanide compounds, such as the phosphates found in coal, have very high melting, boiling and thermal decomposition temperatures. This allows them to survive when the coal is combusted or gasified in power plant operations. The REEs remain in the post-combustion and post-gasification byproducts, in a more concentrated form.
NETL’s Rare Earth Elements Program Overview
DOE-NETL initiated the Rare Earth Elements Program in 2014 to address the feasibility of separating and extracting REEs from coal and coal byproducts, including fly ash, coal refuse and acid mine drainage. The program consists of three core technology areas:
- Enabling Technologies that include identification, sampling and analytical characterization of coal-based resources containing REEs; development of techno-economic models for systems analysis; and development of field and rare earth separation process sensors.
- Separation Technologies that include currently available commercial separation systems and the development of novel, advanced separation and recovery concepts applied to extraction of rare earth elements from coal and coal byproducts.
- Process System Development that includes design, construction and operation of bench- and pilot-scale systems, generating rare earth concentrate product.