In This Issue
Summer Bridge on Critical Materials
June 15, 2024 Volume 54 Issue 2
The summer issue of The Bridge discusses leveraging new and emerging technologies, infrastructure, innovative approaches, and a resilient supply chain to ensure a stable and reliable supply of critical materials far into the future.

Technology and Innovation Enablers for Critical Mineral Production

Wednesday, June 12, 2024

Author: Mark E. Russell, Lindley Specht, Steve Klepper, and Alfred Pandiscio

We must take steps to minimize the supply chain vulnerability of rare earth elements and the environmental impacts of processing them.

In recent years, there has been significant coverage in the general press as well as in policy circles of the challenges and risks facing the United States and allied countries regarding access to and availability of various critical minerals needed to enable the twenty-first century high-technology economy. Industries enabled by such critical minerals as the rare earth elements, lithium, cobalt, nickel, and titanium include the automotive, electronics, semiconductor, and aerospace and defense industries.

Supply chain issues around these materials have impacts spanning the domains of the economy, national security, climate, and technological com­petitiveness. Geopolitical tensions with nations such as China and Russia, which have significant concentrations of certain minerals and their processing, only heighten these concerns. And the war in Ukraine, ensuing international sanctions, and Russian responses to these sanctions have served to highlight the geo­political risks of the supply of critical minerals.

This article will focus on one subset of critical ­minerals, the rare earth elements (REEs), and the implications for the aerospace and defense sector. We will explore technologically driven opportunities and initiatives to reduce risks to this sector from supply chain concentration and vulnerabilities, as well as to reduce environmental impacts from the use of this class of minerals.
 

Russell figure 1.gifThese technology-driven approaches include process innovations to reclaim, reuse, and recycle REE ­materials, which both reduce the need for newly mined and processed materials as well as mitigate the environmental impact of mineral extraction. They also include system-level efforts to “design out” or design around the need for REE materials in key applications that are a source of supply chain risk, reducing the demand for and criticality of these elements.

REEs comprise seventeen metallic elements in group 3/3B of the periodic table, including atomic ­numbers 21 (scandium) and 39 (yttrium), and the entire ­­lanthanide series: atomic numbers 57 (lanthanum) through 71 ­(lutetium) (see figure 1). These elements are not especially rare when measured as a percentage of the earth’s crust; however, they are typically widely dispersed in quantities that can be uneconomic to extract.

REE metals and alloys find uses in numerous industrial and technological applications, including in the aerospace and defense industry for applications such as communications, electric motors, guidance and control systems, and targeting and weapons (Grasso 2013). Underlying REE components used for these purposes are high-field-strength permanent magnets as well as specialty optical and electromagnetic materials, for example, in yttrium-aluminum garnet lasers. As just one example of the diverse industrial applications of REEs, gadolinium (Gd), with atomic number 64, finds many potential uses: in thermomagnetic engines and magnetic refrigeration; in a class of superconductors with applications for electric motors; as a dopant in solid oxide fuel cells; as a contrast agent for magnetic resonance imaging; as a phosphor for x-ray medical imaging; in alloys as thermal barrier coatings for hot sections of aircraft engines; and as a neutron absorber for nuclear reactor shielding.

The current production of REEs is heavily concentrated in China. Figure 2 illustrates the 1994-2022 trend of global REE production, illustrating the concentrated role that China has in the global supply and availability of these critical materials. As noted in a recent Wall Street Journal article (Zhai 2021), “Estimates of China’s dominance of the rare-earth industry vary. Some analysts say China mines more than 70% of the world’s rare earths and is responsible for 90% of the complex process of turning them into magnets. A White House report has estimated that China controls 55% of the world’s rare-earth mining and 85% of the refining process.” As a result of this concentration of worldwide REE production and the criticality of these materials to national security systems and capabilities, the US government has taken actions over the years to assess the REE supply chain and ensure the adequacy of supply.

Russell figure 2.gif

Technology and Innovation Enablers

As most are aware, the extraction and separation of REEs from various feedstocks is a difficult yet important task in the supply chain of these materials. Also, given their chemical similarity, these elements are typically difficult to separate from one another and purify. At present, the typical method of extraction and separation from ore feedstock involves the use of strong acids (HCl, H2SO4, etc.) and other chemicals. While a detailed description of the various separation methods developed to date is beyond the scope of this article (Xie et al. 2014), a typical solvent extraction process might involve the use of a phosphoric acid ligand and many stages of solvent extraction to facilitate the mass transfer of the desired material (REE) between the two immiscible aqueous and organic phases. Further separation of the similar elements in this series can be realized by further exploiting small differences in their basicity or other small chemical differences.

The process results in large quantities of toxic, environmentally unfriendly waste that need to be dealt with. While the United States was a dominant player in this supply chain many years ago when these materials were introduced, its position has been replaced by China. To a large extent this transition was precipitated by the differing costs associated with the handling of this toxic waste stream and associated environmental impacts. To address this Chinese dependency, especially for defense applications, mining and processing capabilities are being established (or re-established) in areas such as the western United States (the Mojave Desert area) and the ­Australian outback regions in their typical mining areas. While one can co-locate the mining and processing operations, it should be noted that these current extraction and separation methods tend to require large amounts of water (and thus waste), which may not be in abundance at the actual mining location.

If the United States plans on returning to its position as a dominant supplier of these refined materials, it must both accept and deal with the higher cost of disposing of this toxic waste stream, which may also contain low levels of radioactivity due to the presence of uranium and thorium. Or the United States must develop a method of significantly reducing this toxic by-product and associated costs. Taking the latter view that reducing the total amount of waste is preferred, let’s look at some of the possible methods to achieve this, of which there are at least four.

There are environmental waste considerations associated with REE processing that need to be addressed as we expand domestic production.

The first approach involves the use of higher-efficiency separation materials, such as improved ligands in the current process or improved adsorbents. One example of a novel bio-inspired separation process utilizes the REE-selective lanmodulin protein (LanM) (Dong et al. 2021). This material has shown a high affinity for REEs and can be immobilized onto porous microbeads for use in a low-pH solid-liquid extraction process. This has the advantage of utilizing a lower total solvent amount and, thus, lower waste stream generation, together with the desorption of the REE and subsequent reuse of this adsorbent media. Another advantage of increased extraction efficiency is that lower-grade feedstocks can be utilized. In the mining operation, one prefers to use the highest-grade ore available, for obvious reasons. The use of lower-grade (concentration) feedstock opens up the possibility of repurposing other “waste” supplies, such as coal ash and mining tailings. Low environmental impact work is underway in this area; however, more work is required to mature these processes enough to be economically viable.

The second approach is to take advantage of current electronic waste (e-waste) for recycling to extract the REEs (and other useful materials), either via manual dis­assembly, magnetic separation after processing, or other means. Apple (2022), for example, has developed robotic methods for disassembling its products and extracting the various components for recycling. Currently a significant fraction of the REEs used in Apple products come from recycling. Another process uses an aqueous copper salt-based process to extract REEs from shredded e-waste, thus bypassing the use of strong acid solutions. While much more work remains to be done, various companies (Wayman 2023) are developing these recycling ­approaches to add to the overall supply chain. It should be noted that, as with most recycling efforts, while they can provide a significant addition, they do not typically supplant the need for more “original” materials. Thus, while the concentration of REEs in appropriate e-waste can be high, it does remain a challenge to cost-effectively extract and repurpose these materials. Additionally, as larger market products, such as electric vehicles, reach their end of life, the source of REEs for recycling will increase along with the financial incentives.

The third approach involves the incorporation of allied countries’ capabilities (in addition to those of the United States) into the US supply chain. Australia has one of the largest mining and processing capabilities[1] in the world, and Japan is one of the largest rare earth magnet fabricators (Okinaga 2022). These resources can thus augment the US supply chain to reduce dependency on Chinese raw materials and finished products. Recently, the United States, along with Australia, Canada, the United Kingdom, Japan, and other countries, entered into the Minerals Security Partnership (MSP) (Home 2022). According to the US Department of State (2022), “The goal of the MSP is to ensure that critical minerals (including REEs) are produced, processed, and recycled in a manner that supports the abilities of the countries to realize the full economic development benefit of their geological endowments.”

The fourth approach involves alternative solutions that do not involve the use of REEs. Since high-field magnets, such as ones using Nd2Fe14B, are the focal point here, one can point to recent research (Wang 2020) into the possibility of using iron nitride (Fe16N2) as one possible future replacement for neodymium-based magnets.[2] For most applications, one wants a high-energy product ((BH)max) and high saturation magnetization (Ms), along with other desirable properties. Iron nitride, while still early in develop­ment, has the potential to meet these expectations. One potential limitation is the lower ­thermal stability of the appropriate phase of this ­material, which may limit applications to a lower-temperature regime (<150oC). While much of the experimental properties of this material have been measured in various thin film forms to date, more recent work has been exploring the synthesis of this material in bulk form. This has entailed various low- and high-temperature nitridation methods utilizing, for example, nanoparticles or other starting form factors, followed by subsequent sintering or other methods to form the bulk product.

Summary

There is a recognized need to re-establish more domestic, or at least non-Chinese, supply chains for processed REEs. There are environmental waste considerations associated with REE processing that need to be addressed as we expand domestic production. Recent technological advances in the separation and extraction of these compounds and the use of alternative compounds may be able to help overcome some of these environmental (and thus cost) issues to establish a more environmentally friendly domestic capability in the near future.

References

Apple. 2022. Environmental Progress Report. Cupertino, ­California.

Dong Z, Mattocks JA, Deblonde GJ-P, Hu D, Jiao Y, ­Cotruvo JA Jr., Park DM. 2021. Bridging hydrometallurgy and bio­chemistry: A protein-based process for recovery and separation of rare earth elements. ACS Central Science 7:1798−808.

Grasso VB. 2013. Rare Earth Elements in National Defense: Background, Oversight Issues, and Options for ­Congress. Congressional Research Service Report R41744. ­Washington, DC.

Home A. 2022. U.S. forms ‘friendly’ coalition to secure critical minerals. Reuters, June 30.

Xie F, Zhang TA, Dreisinger D, Doyle F. 2014. A critical review on solvent extraction of rare earths from aqueous solutions. Minerals Engineering 56:10–28.

Nassar NT, Alonso E, Brainard JL. 2020. Investigation of U.S. Foreign Reliance on Critical Minerals—U.S. Geological Survey Technical Input Document in Response to Executive Order No. 13953 Signed September 30, 2020. Open-File Report 2020–1127, Version 1.1. US Department of the ­Interior, US Geological Survey. Washington, DC.

Okinaga S. 2022. Hitachi Metals developing EV motors with less China rare earths. Nikkei Asia, Dec 8.

US Department of State. 2022. Minerals security partnership, June 14. Online at www.state.gov/minerals-security-­partnership/.

Wang J-P. 2020. Environment-friendly bulk Fe16N2 permanent magnet: Review and prospective. Journal of Magnetism and Magnetic Materials 497(1):165962.

Wayman E. 2023. Recycling rare earth elements is hard. Science is trying to make it easier. Science News, Jan 20.

Zhai K. 2021. China set to create new state-owned rare-earths giant. Wall Street Journal, Dec 3.

 


[1]  For example, see lynasrareearths.com.

[2]  See NironMagnetics.com.

About the Author:Mark E. Russell (NAE) is senior vice president and chief technology officer, Lindley Specht is principal engineering fellow, Steve Klepper is principal engineering fellow, and Alfred Pandiscio is vice president, defense technology, all at RTX Corporation.