The Future of Rare Earth Elements May Lie with Coal
By Mary Anne Alvin, Evan Granite and Charles Miller, DOE National Energy Technology Laboratory
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.
NETL’s overarching goals are to develop separation technologies that can be economically deployed to enable domestic supplies of rare earths, and to reduce environmental impacts during REE production from coal-based resources. NETL’s current goals are to validate by 2020 the technical and economic feasibility of prototype systems to produce high purity, salable REEs.
In-house Research at NETL
Rare earths are actually not that rare. However, it is unusual to find them in large concentrations. To overcome this hurdle, NETL’s in-house research is focusing on all stages of REE recovery from coal and coal-based products, including field sampling, characterization, separation and extraction, and computer modeling.
NETL developed techniques for characterizing samples returned from the field as well as produced in the lab. More than 800 field samples have been collected since June 30, 2015, by NETL in-house researchers and personnel from NETL’s headquarters – DOE’s Office of Fossil Energy. The United States Geological Survey and the Electric Power Research Institute have both signed memorandums of agreement with NETL calling for additional collaborative field sampling activity.
Rare earth characterization efforts by NETL are among the most advanced in the world. Researchers at the lab employ a variety of techniques, including digestion methods for the accurate determination of trace REE contents by inductively coupled plasma mass spectrometry – a technique that minimizes uncertainty in trace REE determination.
After determining what rare earths are present and in what quantities, the next step in obtaining the valuable materials involves separation and extraction techniques. NETL is developing these capabilities for use with coal‐based resources such as coal, coal refuse, clay and sandstone over- or under‐burden materials, aqueous effluents and power generation ash.
NETL’s multifaceted in-house research is helping to establish a reliable domestic supply of rare earths. The U.S. consumes around 16,000 to 17,000 tons of REEs each year, and this demand could be met by completely extracting rare earths from domestic coal and coal byproducts. For example, a typical coal sample contains 62 parts per million (ppm) of total rare earth elements on a whole sample basis. With more than 275 billion tons of coal reserves in the U.S., 17 million tons of rare earth elements are present within the coal.
NETL research engineer Evan Granite said, “By tapping into this vast untouched resource of coal and coal byproducts, the United States could benefit from a 1,000-year supply of REEs at the current rate of consumption.”
In addition, the U.S. typically produces around 100 million tons of coal fly ash annually and this ash typically contains more than 400 ppm of total rare earth elements. Clays and shales located above and below coal seams are also a possible source since they can contain around 200 ppm total rare earths.
External Partnerships to Accelerate REE Research
In fiscal year 2016-2017, congressional language expanded the REE program’s objectives to include external agency activities for development and testing of commercially viable advanced separation technologies at proof-of-concept or pilot-scale stages. The initiative called for near-term deployment of the innovations enabling the extraction and recovery of rare earths and minerals from U.S. coal and coal byproduct sources with the highest potential for success. To accomplish this, NETL reinforced its robust in-house research with partnerships in industry and academia. NETL federal project manager Charles Miller said, “The DOE-NETL REE program portfolio currently comprises 14 active external projects, and they are achieving remarkable success.”
For instance, NETL manages five bench-scale and four pilot-scale projects, initiated in March of 2016, that are making significant progress in developing high-performance, economically viable and environmentally benign technologies to recover rare earths from domestic coal and coal byproducts. Within the first six months of the projects, partners achieved a production of ≥ 2 percent by weight REE pre-concentrates from coal-based materials. In addition, more than 90 percent REE recovery has been demonstrated from acid mine drainage materials.
These projects included sampling and characterization of REE-bearing feedstocks, laboratory testing of processes to extract rare earths from those feedstocks, and design of bench-scale and pilot-scale systems to recover REEs from the feedstocks. They involved research leaders in academia and industry, including Battelle Memorial Institute, Duke University, the University of North Dakota, the University of Wyoming, West Virginia University, Physical Sciences Inc., the Southern Research Institute, the Tusaar Corporation and the University of Kentucky. Project researchers are working to identify innovative processes using existing separation technologies and process designs that will address the environmental, safety and health impacts of byproducts, and then optimize the overall economics of the REE separation and recovery process.
Additionally, NETL manages five other projects that began in October of 2016, to identify and characterize domestic coal and coal byproducts containing high rare earth concentrations. These projects consist of work to identify, locate, field-sample and analyze materials from various regions of the country, including coal basins such as the Illinois Basin, Northern Appalachian in Pennsylvania and West Virginia, Central Appalachian in West Virginia and the Raton Basin in Colorado and New Mexico.
Recently, NETL has further expanded its external work by selecting new projects to design systems that will achieve small-scale production of salable REEs in the form of final products such as individual rare earth compounds. It is expected that one or more of these projects will be in operation by 2020.
According to NETL REE technology manager Mary Anne Alvin, “As the current REE program grows, we anticipate that the REE research portfolio will expand from not only research conducted in-house and with our current external partners, but also to research involvement with other national laboratories and additional small business innovation efforts.”
Mary Anne Alvin is REE technology manager, Evan Granite is research engineer and Charles Miller is project manager at the Department of Energy’s National Energy Technology Laboratory.