The United States is dependent on China and other offshore sources for numerous critical materials that are essential to our Nation’s economy and national security. These include medical and pharmaceutical goods, rare earth elements (REEs), and other critical minerals (CMs). Transitioning the production of these materials and their associated supply chains back to the U.S. is a strategic priority, as evidenced by recent and proposed legislation as well as by several Executive Orders, including the President’s recent declaration that the supply chain threat to critical minerals is a national emergency [1,2]. Consequently, research, development and demonstration (RD&D) efforts to create new domestic sources of CMs and REEs have been accelerated with the goal of making our domestic supply chains more resilient.
To address the challenge of leading our Nation to secure national independence from REE offshore reliance, the Department of Energy (DOE), Office of Fossil Energy (FE) and the National Energy Technology Laboratory (NETL) in 2014, performed an initial assessment under its Feasibility of Recovering Rare Earth Elements program, to assess the potential recovery of REEs from coal and coal by-products which included run-of-mine coal, coal refuse (mineral matter that is removed from coal prior to shipment), clay/sandstone over/under-burden materials, ash (coal combustion residuals), and aqueous effluents such as acid mine drainage (AMD), and associated solids and precipitates resulting from AMD treatment. After reporting its findings in the DOE 2015 Report to Congress , the Department initiated a multi-year research, development and demonstration (RD&D) effort to demonstrate both the technical feasibility and economic viability of extracting, separating and recovering REEs from these domestic coal-based resource materials. Basic and applied science research projects were conducted at national laboratories, small business organizations and at numerous universities which led in 2016 to the design, construction and operation of bench- and small pilot-scale facilities, and in 2018 to the production of small quantities (e.g., ~100 gm/day) of 90% (900,000 ppm) high purity, mixed rare earth oxides (MREOs) using conventional physical beneficiation and chemical (hydrometallurgical) separation processes. Currently, state-of-the-art, conventional separation, process system concepts are being assessed for near-future production of 1-3 tonnes/day of high purity, mixed rare earth oxides (MREOs) from coal-based resources in engineering prototype facilities.
In order to comply with Executive Order 13817, DOE-NETL’s program expanded its technology development effort in 2019 to include the recovery of critical minerals (CMs)  from coal-based resources. As a result, DOE-NETL’s program in 2020, renamed as the Critical Minerals Sustainability program, required existing domestic small pilot-scale facilities to co-produce CMs in addition to producing REEs. In 2021, DOE-NETL’s program plans to initiate basinal coalition efforts to address realization of the full economic potential value of U.S. natural resources for producing REEs, CMs, and high-value, nonfuel, carbon-based products, and to holistically assess not only upstream mining of resources and physical separation (e.g., beneficiation), but also midstream processing, separation, recovery and purification of critical and high-value materials, and ultimately onshore downstream manufacturing that incorporates these materials into commodity or national defense products.
As part of the lanthanide series (Figure 1) of elements, REEs are essential materials that are used in a broad range of technologies that are significant to domestic and national security, energy, and daily consumer products. REEs include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Th), yterrbium (Yb), lutetium (Lu), and the transition elements scandium (Sc) and yttrium (Y). Critical REEs are those deemed as being a potential supply risk and are highly important to future U.S. clean energy technologies.
REEs typically occur at low concentrations throughout the earth’s crust. REEs are not found in an isolated form readily available for extraction but are distributed throughout a variety of minerals as monazite, bastnaesite and xenotime, and can also be found in coal-based resources. REE-bearing mineral deposits are relatively rich in either light rare earth elements (LREEs) or heavy rare earth elements (HREEs), with the LREEs being more abundant (Figure 2).
As nonfuel minerals or materials, CMs are essential to our modern economy and national security and that have a supply chain vulnerable to disruption. CMs include aluminum (bauxite), antimony (Sb), arsenic (As), barite (BaSO4), beryllium (Be), bismuth (Bi), cesium (Cs), chromium (Cr), cobalt Cr), fluorspar (CaF2), gallium (Ga), germanium (Ge), graphite (natural), hafnium (Hf), helium (He), indium (In), lithium (Li), magnesium (Mg), manganese (Mn), niobium (Nb), platinum group metals, potash, the rare earth elements group, rhenium (Re), rubidium (Rb), scandium (Sc), strontium (Sr), tantalum (Ta), tellurium (Te), tin (Sn), titanium (Ti), tungsten (W), uranium (U), vanadium (V), and zirconium (Zr). The average mean CM concentration in coal and select alternate materials is shown in Figure 3.
China has been the dominant supplier of REEs since 1988, providing 95 percent of the global REE market in 2011 (Figure 4). As recently as 2011, decisions by China to restrict exports and favor its own domestic industries resulted in REE price volatility. Consequently, rising concern among industrialized nations has driven the resurgence of global interest in REE mineral exploration and extraction, and related research on supply, demand, utilization, recycling, reuse, and substitution. Several new commercial REE projects are in various stages of planning and development and are focused on diversifying supply. In contrast, new efforts to purify and refine REEs are limited.
The U.S. now imports 80 percent of its REE demand directly from China, with portions of the remainder indirectly sourced from China through other countries. For 31 of the 35 CMs, the U.S. imports more than half of its annual consumption. The U.S. has no domestic production for 14 CMs and is completely dependent on imports to supply its demand .
A better understanding of the REE-CM supply chain and economics is required to reduce the barriers to domestic REE-CM production and to identify policy drivers needed to reduce investment risk. To address this, NETL has and continues to develop an extensive understanding of the existing and projected REE-CM markets and evaluates potential production pathways to identify technical or economic barriers to deployment.
In 2014, DOE ‘s Office of Fossil Energy (FE) and NETL undertook the mission of expanding the nation’s supply of REEs, with an initial focus placed on addressing the feasibility of extracting, separating, recovering and purifying these materials from coal-based resources. Through that effort NETL identified promising domestic REE-containing coal-based resources and demonstrated the production of high purity REEs in bench- and small pilot-scale facilities. The program is now poised to take the next step in demonstrating the feasibility of producing REEs and potentially CMs through the design, construction and operation of an engineering-scale prototype facility. The operation of this facility, in conjunction with complementary R&D efforts to develop advanced transformational separation and production processes, establish our Nation’s path forward for the operation of economically viable, domestic, commercial-scale, REE-CM separation and production facilities.
The mission of DOE-NETL’s program since 2014 has been the development of an economically competitive and sustainable domestic supply of REEs to assist in maintaining our Nation’s economic growth and National Security. The program was expanded in 2020 to include CMs.
The objectives of the DOE-NETL program from 2014-2020 were to
The goals of the DOE-NETL 2014-2020 program were to validate both the technical as well as economic feasibility of recovering REEs and CMs from coal-based resources. In 2019-2020, the program was accelerated to design, construct and operate a domestic engineering-scale prototype facility in an environmentally benign manner, producing in the near-term 1-3 tonnes/day of mixed rare earth oxides or salts (MREOs/MRESs) from coal-based resources at purities of a minimum of 75% .
Based on Congressional language, in 2014-2015, DOE-NETL performed an assessment which analyzed the feasibility of economically recovering REEs ,from coal and coal by-products [14-15]. In 2016-2018, the program was directed to expand its external agency activities to develop and test commercially viable advanced separation technologies at proof-of-concept or pilot-scale that can be deployed near-term for the extraction and recovery of REEs and minerals from U.S. coal and coal by-product sources having the highest potential for success [16-18]. In 2019-2020, the program was directed to continue its external agency activities to develop and test advanced separation technologies, and as previously discussed, to accelerate the advancement of commercially viable technologies for the extraction and recovery of REEs and CMs from U.S. coal and coal by-product sources [19-20].
As shown in Figure 5, the program consisted of three core technology areas which include
The over-arching mission of DOE-NETL’s REE and CM program has been the development of an economically competitive and sustainable domestic supply of these critical materials within the U.S. Achieving this mission has been through research conducted in field work proposal (FWP) projects at NETL’s Research and Innovation Center (RIC), as well as at alternate DOE national labs including the Los Alamos National Laboratory (LANL), Lawrence Livermore National Laboratory (LLNL), Idaho National Laboratory (INL), and Pacific Northwest National Laboratory (PNNL).
Similarly, collaborative RD&D projects were conducted through funding opportunity announcement (FOA), requests for proposal (RFP) awards with industrial stakeholders and numerous universities, and projects awarded under Small Business Innovation Research (SBIR) programs.
As a fully integrated RD&D program (Figure 6), DOE-NETL’s efforts have uniquely spanned across basic and applied science and technology development (e.g., Technology Readiness Level (TRL) 1-3), through engineering design, construction and operation of bench- and small pilot-scale separation facilities (TRL 3-5), and to the development of process designs for the operation of near-future engineering-scale prototype facilities (TRL 5-7).
Between 2014 and 2018, DOE-NETL’s program was funded at a level of $15M/yr and consisted of over 30 active projects. In 2019 and 2021, funding was increased to $18M and $23M, respectively. Additional small business innovation research (SBIR) REE projects were conducted in conjunction with the Office of Science.
NETL’s Research and Innovation Center (RIC)
NETL’s RIC FWP portfolio has been focused on four core competency areas. These include: (1) Locating promising candidate REE-CM resources and potential reserves; (2) Discovering and mature technologies to extract and concentrate REEs-CMs; (3) Reducing technology maturation time and risk of technology commercialization through advanced modeling and analysis; and (4) Enabling process intensification and rapid deployment. A discussion of each of NETL RIC’s core competencies as related to REE and CM research efforts, and respective project technical accomplishments follow.
Since 2015, NETL RIC has conducted extensive field prospecting campaigns to locate potential candidate REE-containing coal-based materials. Efforts to identify promising resources are based on (a) understanding “how” REEs are present within the various materials (e.g., chemical phase composition and concentration), and to “what extent” REEs can be separated and recovered (e.g., extractability), and (b) developing a systematic method to predict “where” these resources may exist.
Classic x-ray diffraction (XRD), scanning electron microscopy (SEM) and microprobe analyses, and cutting-edge analytic characterization techniques as x-ray absorption near-edge structure (XANES) analysis at the SLAC National Accelerator Laboratory have been utilized to address the “how”, which underpins the basis for development of novel extraction techniques (Figure 7). Questions as “what phase and oxidation state these elements are in” provide insight on what is being selectively targeted during extraction, and what portion of the host rock can be discarded during processing.
Understanding the “where” promising resources may exist is being addressed by the development of a method and tool to systematically identify high concentration and extractable REE-CM deposits in sedimentary systems. As it is not currently possible to predict these locations, the basis for NETL initiating development of the REE-SED Assessment Method and tool in 2018 was to support systematic prediction and assessment of domestic REE deposits from coal-based resources and other sedimentary systems [21,22]. This method is the first-of-its-kind, big-data, machine learning (ML)-enabled, geoscience approach to improve prediction and identification of domestic sedimentary and coal-based resource and deposit locations containing high concentrations of REE and CM (Figure 8). This effort in collaboration with industry, university and the USGS, as well as state surveys has been key to NETL’s geo-data science modeling effort which relies on data generation from strategic analysis of samples at the local scale. Looking ahead, REE-SED has unlimited potential and is expected to dramatically reduce the time required to locate potentially “new” promising REE or CM deposits.
RIC has been successful in producing < 95% purity (<950,000 ppm) MREO from a variety of sources, including waste products such as coal ash, acid mine drainage, and other materials resulting from legacy mining operations. Since 2015, REE extraction and recovery research at NETL RIC has included not only physical and chemical separation efforts, but also development of advanced sorbent materials for sorption (e.g., capture) of REEs in naturally occurring coal waste streams or REEs from extraction and separation process fluids. These transformational efforts have ranged from lower TRL basic laboratory-scale research to field testing of advanced sorbents at the Pittsburgh Botanical Garden, a former abandoned mine site in Pennsylvania (Figure 9). A 2020 technology commercialization funded (TCF), small pilot-scale project was initiated in collaboration with the University of Wyoming School of Energy Resources and other industrial partners, to advance RIC’s extraction and separation process for recovery of REEs from calcium-enriched Powder River Basin ashes.
In addition to the development and maturation of production processes, RIC’s technology development has systematically addressed other technology areas to promote the creation of a domestic REE and CM industry. This effort includes the development of computational flow dynamic (CFD) models and real-time laser induced breakdown spectroscopy (LIBS), metal organic framework (MOF)-ultraviolet light source (UV) and fiber optic sensors, to enable process control in systems that typically operate at steady state. CFD modeling and sensor development can enable process optimization and accelerate process intensification (reducing costs), as well as assist to de-risk deployment of potential REE-CM facilities (Figure 10).
Techno-economic assessment (TEA) of separation processes has also been utilized to reduce research and development time. By identifying key areas for process optimization early in the R&D process, researchers can identify and focus on the metrics that impact cost and performance. TEA has been extensively utilized to support validation of REE-CM separation and extraction processes developed in DOE-NETL extramural stakeholder projects. NETL RIC researchers have also developed a current and projected future REE and CM intermediate and end-product supply chain database.
Extramural REE-CM Research
Technology development in DOE-NETL’s federally funded extramural projects has also systematically focused on field prospecting and resource assessment; integration of conventional physical beneficiation and chemical separation or hydrometallurgical processing of feedstock materials to produce high purity coal-based MREOs; development of advanced, new-novel, transformational separation processes; techno-economic assessment (TEA) of conventional and transformational separation processes; and optimization and efficiency improvement of conventional separation processes to achieve system economic viability.
Since 2016, numerous extramural stakeholder extraction separation and recovery processing approaches have been identified and used to demonstrate the technical feasibility of extracting REEs from coal, coal refuse, power generation ash and AMD (Figure 11). By 2020, these efforts have resulted in the design, construction and operation of three first-of-a-kind, small pilot-scale facilities producing small quantities (e.g., ~100 gm/day) of >98-99% (>980,000-990,000 ppm) high purity, MREOs from 300 ppm REE-containing coal-based feedstock materials using conventional physical beneficiation and hydrometallurgy (chemical separation) processes.
In 2018, the University of Kentucky produced small quantities of 80-90wt% (800,000-900,000 ppm) pure mixed rare earth oxides (MREOs) in its modular pilot-scale facility (Figure 12), from coal refuse materials from the Central Appalachian and Illinois Coal Basins. Forty-five percent of the critical elements in the University of Kentucky’s REE concentrate were neodymium and yttrium which are used in national defense technologies and the high-tech and renewable energy industries. In 2020, 98% pure MREO concentrates were produced with co-production of CMs.
Commissioned in July 2018, West Virginia University (WVU) bench/small pilot-scale rare earth extraction facility (Figure 13) began producing REE pre-concentrates from acid mine drainage (AMD) and sludge materials from the Appalachian Coal Basin. By 2019, WVU produced approximately 80wt% (800,000ppm) pure MREO concentrate, and in 2020, WVU succeeded in producing approximately 98wt% (980,000ppm) pure MREO concentrates from AMD with co-production of CMs.
In July 2018, Physical Sciences Inc., produced greater than 15wt% (150,000ppm) MREOs in their micro-pilot facility (Figure 14) in Andover, Massachusetts, using post-combustion ash that was generated in a Power Plant boiler that was burning East Kentucky Fire Clay coal. The micro-pilot facility was used by PSI to develop the design and operating parameters that were used to scale their process to the pilot-scale operating system with Winner Water Services in Sharon, PA. The PSI-Winner Water pilot-scale facility became operational in November 2019.
In 2019, the University of North Dakota demonstrated in their bench-scale facility (Figure 15) the capability of producing a 65wt% (650,000 ppm) MREO concentrate from lignite using a one-step selective mineral acid leaching process. Efforts are continuing at the University of North Dakota to bring on-line their pilot-scale facility in 2021.
Numerous additional technical contributions have resulted from conduct of the extramural stakeholder projects. For example, researchers at West Virginia University have demonstrated that nearly 100% of the REEs in AMD can be recovered, and that when REEs are extracted from small AMD material drying cells (e.g., ~0.5 acre x ~10-ft deep (Figure 16)), an estimated revenue of $250,000 (or greater) can result.
Researchers at the University of North Dakota have shown the relative ease of extracting REEs that are primarily contained in the organic fraction of lignite using a one-step selective mineral acid leaching process.
Researchers at the University of Kentucky in collaboration with the University of Utah have incorporated in-situ sulfuric acid production through microbially-enhanced heap leaching of pyrite in feedstock materials, improving coal refuse processing economics.
Each of these small-pilot-scale MREO facilities are currently implementing process design configurations for co-production of select CMs as Co, Mn, Ni, Ga and Gd.
In collaboration with Battelle Memorial Institute, Rare Earth Salts (RES) produced the first individually separated, high purity (>95%) REO from coal-based materials in 2020.
Researchers at Los Alamos National Laboratory (LANL) have shown the feasibility of transitioning proven actinide separations processing technology to the separation and recovery of REEs from the lanthanide series, as well as the planned development of a portable LIBS-Ramen backpack, similar to that planned for soil exploration on Mars, for determination of the REE concentration and chemical phase composition in solid coal-based materials.
Technology achievements resulting from both intramural and extramural projects has successfully demonstrated the potential for the utilization of coal and coal-based resources to produce critical elements needed for the U.S. to drive towards the development of refineries that are essential for domestic commodity and defense product production. DOE-NETL’s program is additionally on-point to realize the full potential value of coal-based resources, transforming the use of coal in today’s U.S. domestic coal industry.
The uniqueness of DOE-NETL’s program is its capability to not only impact both domestic and global technology integration across numerous supply chains and markets, but also to facilitate cross-functional technology development in and between DOE-NETL’s Coal Crosscutting Materials Research, Turbine, Fuel Cells, and Advanced Coal Processing Technology Programs, as well as DOE-NETL’s Oil and Gas Technology programs.
When viewed in its entirety, the REE and CM supply or value chain consists of mining, separation, refining, alloying, and ultimately manufacturing devices and component parts (Figure 17). A major issue with respect to critical material development in the U.S. is the lack of refining, alloying and fabricating capacity to domestically process these materials . In order to achieve domestic self-reliance, ensuring a stable, sustainable REE and CM dual-use supply chain — from mine to manufactured product (Table 1) — is critically essential for clean energy and high-value defense platforms.
Notably, approximately 40% of mined rare earth production is reduced to metals and alloys, including most of neodymium (Nd), samarium (Sm), and dysprosium (Dy), for applications such as neodymium metal for Nd-Fe-B permanent magnets, samarium metal for Sm-Co permanent magnets, lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd) for rechargeable battery electrodes .
By creating a sustainable domestic REE and CM supply chain, the U.S. would reduce its risk of supply disruption for essential domestic and military industries, would have the potential to produce intermediate products and manufacture end-use products onshore which are currently valued above $1.2-trillion, and would prevent the U.S. from being left behind in the emerging clean energy technology market. A 40% growth of the current $5-billion global REE market is projected in the next five years, with similar growth projected for the CM market.
Recent U.S. demand for REEs is approximately ~13,000 tonnes/year (annual consumption varies) . The estimated distribution in 2019 of rare earths (as oxides) based on end use was 75% catalysts, 5% metallurgical applications and alloys, 5% ceramic and glass, 5% polishing, and 10% other . In 2010 and 2012, the Department of Defense (DoD) indicated that military consumption accounted for less than 5% of domestic REE consumption (approximately 800 tonnes/yr) that was associated with national security needs [27-28].
Domestic production of REEs and CMs from coal-based and/or alternate resources clearly supports our Nation’s clean energy and economic security needs. Currently, the dominant U.S. end uses for REE are for automobile catalysts and petroleum refining catalysts; use in phosphors in color television and flat panel displays (cell phones, portable DVDs, and laptops); permanent magnets and rechargeable batteries for hybrid and electric vehicles; metal alloys; glass polishing; ceramics; and numerous medical devices. Permanent magnets containing neodymium (Nd), gadolinium (Gd), praseodymium (Pr), dysprosium (Dy), and terbium (Tb) are used in numerous electrical and electronic components and new-generation generators for wind turbines . In addition, critical minerals are used in permanent magnets for wind turbines and electric vehicles, fluorescent lighting, light-emitting diodes (LEDs), photovoltaics, batteries for electric vehicles and storage, catalytic converters, fuel cells, gas turbines, hydrogen electrolysis, nuclear power, thermoelectrics, and vehicle light weighting.
Similarly, as dual use materials, domestic production of REEs and CMs from coal-based and/or alternate resources supports our Nation’s defense and national security needs. Defense applications that utilize REEs include jet fighter engines, missile guidance systems, antimissile defense, and satellite and communication systems. Critical minerals are additionally used in defense satellite communication equipment, guidance systems, military vehicles, armor, ammunitions, hardware and imaging.
Building on the accomplishments achieved between 2014 and 2020 in DOE-NETL’s Feasibility of Recovering Rare Earth Elements program, and aligning the program to further support Executive Order 13817 , the following five areas are identified for conduct in DOE-NETL’s Critical Minerals Sustainability program:
R&D efforts in the Critical Minerals Sustainability program will continue to enable the recovery of CMs, including REEs throughout the supply chain. Understanding the basinal deposit relationships of these CMs and REEs from carbon ore (e.g., coal, coal by-products, and coal waste streams such as acid mine drainage and fly ash), other ores, mining by-products, abandoned mines and other valuable sources will enable projects to address resources holistically. Advanced technologies developed throughout the supply chain and co-production business models, will continue to improve the economics of future projects. The program will strive to develop and test in engineering-scale prototype facilities the technologies that industry will need to establish a domestic supply chain to help fuel our nation’s economic growth, transition to clean energy technologies, secure our energy independence by reducing our reliance on foreign sources, and increase our national security.
DOE-NETL’s rare earth element and critical minerals program has demonstrated the first step towards national independence from reliance on offshore REE and CM suppliers through its 2014-2020 RD&D efforts using coal-based resources to produce small quantities of high purity MREOs and CMs. Leveraging accelerated production of these materials in engineering-scale prototype, demonstration and commercial facilities, in parallel with the return of onshore component manufacturing, will facilitate not only self-reliance but also Made in America across numerous critical clean energy and defense product lines and supply chain markets.
External stakeholders who were previously under contract to NETL, external stakeholders who are currently participating on projects, NETL Research and Innovation Center (RIC) scientists and engineers, NETL Federal Project Managers, and Fossil Energy Program Managers are acknowledged for their many contributions to DOE-NETL’s Feasibility of Recovering Rare Earth Elements and Critical Minerals Sustainability program.