Rare Earth Metals and Minerals Industries

Four conventional mineral deposit types—carbonatite, alkaline igneous, heavy mineral sand, and regolith-hosted ion-adsorption clay deposits—currently supply global markets with the rare earth elements (REEs) and rare earth oxides (REOs) necessary to meet the technological needs of global communities. The unique properties of REEs make them useful in a wide variety of applications, such as alloys, batteries, catalysts, magnets, phosphors, and polishing compounds. Rare earth element minerals are complex in both composition and structure. Carbonate, oxide, silicate, and phosphate-type minerals contain highly variable amounts of rare earths. Most rare earth-bearing minerals contain mainly lighter rare earths, a mixture of all the rare earths, or only the heavier rare earths.

Diverse technological applications require the full range of light, middle, and heavy rare earths. The production of these elements, in particular the heavy rare earths, remains highly dependent on deposits from China. Diversification of rare earth supply chains is contingent on expanded knowledge of globally distributed resources and an understanding of the degree to which those resources have been explored and evaluated. The knowledge of tectonic setting, typical rock associations, deposit morphology, and deposit genesis has led to the discovery of many conventional-type rare earth deposit types. Recent developments are anticipated to result in further discoveries that have the potential to meet the ever-expanding applications of REEs and REOs to address modern societal needs.

Energy-related materials such as coal, coal-bearing wastes, and coal combustion products are traditionally thought of as sources or by-products of electric power generation. Increasingly, these materials are considered resources for their content of rare earth elements (REEs) and other useful constituents. In this chapter, we examine the distribution, modes of occurrence, and relative extractability of REEs from coal-derived materials. We also consider economic factors associated with recovery of REEs from these sources. While several coal-derived sources show promise for REE recovery at the pilot scale, in all cases, REE contents are much below those of primary ores, such that extraction and concentrating the REEs require new and innovative approaches that are largely developmental.

Among coal-related sources, fly ash is the most REE-enriched, as REEs from coal are strongly retained in these refractory solids remaining after coal combustion. Partitioning of coal-derived elements into fly ash has been known for decades but this has yet to be commercially exploited. A key drawback shown in this chapter is that a significant fraction of REEs in fly ash is contained in highly insoluble aluminosilicate glasses that make up the largest portion of this material. In addition to testing chemical or physical pretreatment approaches to help improve the extractability of REEs from fly ash, current research is applying modern analytical approaches to better understand the distribution of REEs on increasingly smaller scales, in the interest of targeting their recovery.

Next-most REE-enriched among coal-related materials are solid waste products of coal mining and wastes from coal preparation, both of which are REE-enriched relative to coal itself. These waste coals concentrate mineralogical constituents that are excluded during mining or removed during coal preparation because they do not contribute to the heating value of coal for power generation. Recovery of REEs from coal waste has shown promise at the pilot scale and has the added benefit of converting a waste into useful constituents.

Total REE contents of commercial coals are, on average, much below the 300 parts per million interest level for REE recovery set by the U.S. Department of Energy (DOE). However, as reviewed in this chapter, certain horizons within coal beds show preferential REE enrichment and could be targeted by selective mining. Beyond this, certain coals are REE-enriched overall due to their unique geologic histories involving derivation from REE-enriched sediment sources, deposition of volcanic ash during coal formation, or interaction of coal with REE-bearing fluids.

Acidic drainage from abandoned coal mines is produced by the breakdown of pyrite (FeS₂), which is unstable in oxygenated conditions. While these acidic fluids have lower REE contents than any of the coal-based solids described above, they are proportionally enriched in certain heavy rare earths, especially yttrium (Y). Precipitates from coal-based acid-mine drainage concentrate REEs to levels that are of interest for recovery, and these are also promising sources for extraction at the pilot scale.

The lanthanides are more commonly referred to as rare earth elements (REEs). Approximately 250 rare earth minerals (REMs) are known but vary in their composition as solid solutions. Because REEs have similar properties, REMs are usually separated from invaluable gangue into a single bulk concentrate. Flotation is almost universally the method of choice. Flotation is a complex process that works based on differences in hydrophobicity, involving a plethora of variables that enhance those differences with the goal of improving the grade and recovery of the REMs reporting to the concentrate.

In this regard, flotation is briefly reviewed from reagent, machine, and flowsheet design perspectives with application to REMs. It is stressed that REM flotation depends on REE coordination number and cation size, typically requiring the need for collector blends. A case study is then presented to illustrate the importance of depressants. This was accomplished by examining their role on the first-order rate constant in kinetic modeling. Four novel depressants were identified and a parametric design of experiments was conducted. The study looked at the type of depressant and the dosage of collector to generate a statistically significant model using a three-compartmental kinetic approach. Not only were grade and recovery examined but so was the response of the first-order rate constant to changing experimental conditions.

Ion-adsorption clays (IACs) mined in South China are probably the most important rare earth resource in the world, as they account for >80% of the global supply of heavy rare earth elements (HREEs) that are critical for high-tech manufacturing industries. Recent studies conducted by the U.S. Geological Survey (USGS) showed that both the climate and geological condition in the Central Appalachian Mountains were conducive to forming regolith-hosted ion-adsorption clays, which raised the prospect of finding IAC deposits in the region. It happens that ~80% of the mineral matter in coal is clay and/or clay-based sedimentary rocks, while much of the sediments in coal basins are detrital in origin. It is, therefore, the objective of this chapter to discuss the possibility of extracting rare earth elements (REEs) from coal by-products. It appears that IACs are present in coal by-products; however, it is more difficult to extract the REEs from these materials as compared to those in South China. The reasons for the difficulty are reviewed on the basis of the limited experimental and thermodynamic data available in the literature.

The chemical and physical properties of the final application using rare earth elements (REEs) are specific to the different REEs and in most cases, these properties depend on the purity of the REE used. Since RE ores contain a mixture of all the lanthanides plus yttrium, and because the lanthanides and yttrium have similar chemical properties, producing such high purities is a challenge. Currently, this process step commonly called RE separation or RE refinery is done by solvent extraction (SX). Although several companies and research teams are looking for alternative processes, SX remains the only technology used in industry.

Solvent extraction is a combination of chemistry and technology. This chapter presents the chemistry and the technology behind the RE separation process and their consequences on the economics and the environmental footprint of the REE industry. Different combinations of aqueous solutions and organic molecules can be used at industrial scale, but only an overall comparison from ore leaching to the separated individual and blended RE oxide including environmental assessment can decide the best choice for each specific application. Companies mastering the modeling of the REE separations can design and drive an REE separation unit.

Up to now all the industrial units of RE separation use SX operated in mixer-settlers (MS). This technology is mature and very robust but leads to high CAPEX and high REEs inventory. Several teams are trying to overcome this drawback by working on new processes as replacing MS by columns, or by replacing the solvent with a solid phase leading to processes called Solid Phase Extraction (SPE). These efforts are also reviewed.

In the late 1940s, lanthanide separations were performed using ion exchange (IX) as part of the Manhattan project (Boyd et al. J Am Chem Soc 69(11): 2818–2829, 1947; Spedding et al. J Am Chem Soc 69(11): 2812–2818, 1947 which led to the development of ion chromatography techniques enabled the separation and production of large quantities of high-purity rare earths Gscheneidner, Rare Earth; The Fraternal Fifteen: Division of Technical Information; U.S. Atomic Energy Commission, New York, 1967; Fritz, J Chromatogr 1039(1–2): 3–12, 2004).

(Lifton, Solvay’s Toll Refining Services Redirect the Downstream Rare Earth Dream, 2014, https://investorintel.com/markets/technology-metals/technology-metals-intel/first-come-first-served/).

In the more than seventy years since IX was first applied for REE separation, IX resins and the equipment used for separations have advanced significantly. The performance of IX resins with regard to stability, kinetics, and capacity has increased markedly with the development of highly uniform, small monosphere polymer materials. The development of continuous IX contactors has greatly simplified the delivery and control of IX and ion chromatographic separations where a single multiport valve can control 20–30 columns enabling multiple separation stages, recycle steps, and reagent recycling. While IX has continued to be used for rare earth production, the technological advances and improvements in the equipment and chemical media have led to a renaissance in the movement toward reestablishing IX as a separation technique for the production of high-purity rare earths.

Ionic Liquids are room temperature organic molten salts that are being investigated for various metallurgical processing applications. Specifically, the application of ionic liquids (ILs) in the extraction, refining, separation, and reduction of the rare earth elements provides many opportunities for reducing the processing economic and environmental costs. The primary fields of research involve the replacement of organic diluents and extractants in solvent extraction, their utilization in flotation, and their application in electrometallurgy. Additionally, ILs are being investigated as a replacement for water, transitioning from hydrometallurgy to solvometallurgy. Advantages of ILs include their low vapor pressure, high thermal stability, and significant variability in coordination ability. This later advantage allows researchers to design task-specific ILs with targeted characteristics. In electrometallurgy, ILs allow for the electrodeposition of highly water-reactive metals such as the rare earth elements and offer a potential alternative to high-temperature molten salt electrolysis and metallothermic reduction processes.

An overview of the reduction of rare earth elements through metallothermic and electrochemical methods is presented. The basic thermodynamic considerations are discussed. Metallothermic methods are reviewed, including lanthanothermy. Industrial considerations and production of rare earth metals by electrochemistry are addressed, as well as alternatives for rare earth electrodeposition. Lastly, some of the environmental concerns are described.

The reduction to metal of rare earth elements is a complex, energy-intensive, and environmentally damaging process currently undertaken by molten salt electrolysis for the light rare earth elements (lanthanum (La) to neodymium (Nd)) and by metallothermic reduction for heavier rare earth elements ((samarium (Sm) to lutetium (Lu), yttrium (Y), and scandium (Sc)). The primary metals used as reductants in metallothermic reduction processes are calcium (Ca) and La. New approaches such as electrolysis in ionic liquid medium, the FFC-Cambridge, Fueled Anode Electrolysis, and Carboxylate Reduction processes are set to disrupt the current industrial practices. Their development is a sustainability imperative as they promise to offer a significant reduction in environmental impact and in energy usage.

Continuous discoveries of the unique chemical and physical properties of rare earth elements (REEs) throughout history have had a major impact on their industrial applications. Although their first popular use can be traced back as early as 1885, it is in only the 1970s that diversification of uses truly emerged, coeval to the expansion of mining production levels. Thanks to continuous technological progress, REEs have since enabled significant advances in numerous industrial applications. Through an historical perspective and illustrative examples, this chapter shows that two main trends are at the root of such an evolution: (1) the search for substitution technologies following the evolution of consumer’s demand and (2) the fact that REEs are geologically found and extracted as aggregate lanthanide elements. The latter has often led to seeking new applications to by-products in order to maximize economic benefits from their extraction, sometimes bringing key technological breakthroughs along the way.

A comprehensive review of rare earth magnet manufacturing and applications would need several book volumes to cover these topics in detail, so with just a single chapter, the only approach is to provide a brief synopsis of the history, the basics of the manufacturing methods and a few key applications. In terms of value, these materials represent the largest segment of the permanent magnet market and in terms of performance, they have dominated the market since their discovery nearly 60 years ago. As a result of the massive improvement in performance many devices are smaller, lighter, more efficient or lower cost than they would be without them. In some cases, applications would not even be possible without rare earths, particularly those applications that depend on miniaturization. Today, they are used in almost every manufacturing sector but are rarely noticed by the billions of people that benefit from them in daily life. With consistent growth over several decades and with nothing on the horizon to replace them, the future will increasingly depend on rare earth magnets.

This chapter addresses the application of rare earths in petroleum refining, transportation, chemical processing and pollution abatement. Petroleum refining, especially fluid catalytic cracking, is the main area where rare earths are applied as catalysts. Rare earths also find wide application in catalytic converters and in air pollution control in car exhaust. One area that is beginning to see the emergence of the application of rare earths as catalysts is chemical processing, where the introduction of rare earths leads to increased catalyst performance. This chapter reviews the effects of rare earth elements on the structure, activity and stability of these catalysts.

Cerium(IV) oxide (CeO₂) is one of the predominate oxides produced in rare earth mining. Much of it is discarded after separation from the higher atomic number rare earth oxides. A beneficial use of cerium (Ce) is being sought to reduce the cost of producing the more desirable rare earth elements.

Aluminum (Al) alloys containing small amounts of Ce have been investigated to improve their grain refining, casting characteristics and mechanical properties. Cerium containing mischmetal has also been studied in some depth. These additions were usually made at levels of 1 wt% or less and appreciable material property improvement was not evident. Recent work has shown that additions between 4 wt% and the approximate eutectic composition of 10 wt% improve the high-temperature performance of Al alloys.

Corrosion performance of Al alloys can also be improved through the addition of Ce. Traditional Al alloying elements such as magnesium (Mg) and silicon (Si) can be used to control casting characteristics and thermal and physical properties.

The result of using Ce as an addition to Al alloys in multiple manufacturing methods such as additive manufacturing, extrusion and casting is explored in this chapter. Significant strengthening and improved mechanical property retention at elevated temperature has been demonstrated, and in some compositions, complete recovery of room temperature mechanical properties resulted after exposure to elevated temperatures as high as 500 °C for 1000 h.

This chapter reviews commercial applications for scandium (Sc)-containing wrought aluminum (Al) alloys. Advantages from alloying Sc with aluminum Al include (1) refined grain structure in billets, ingots and weldments; (2) increased resistance to recrystallization; (3) strengthening from stable Sc-containing dispersoids and (4) improved nucleation of strengthening phases. These effects are well documented in the literature as highlighted in several detailed reviews.

Efforts to commercialize Sc-containing alloys were initiated in the late 1960s in the Former Soviet Union and at Alcoa in the United States. Alcoa was granted a patent in 1972 covering Sc additions in commercial wrought alloys. Subsequently, hundreds of patents were granted for Sc-containing alloys, but commercial applications have been limited due to Sc availability. In view of current and potential future Sc resources, production of Sc-containing alloys conceivably will find widespread commercial applications once a stable supply market is established.

Ceramic coatings containing rare earth oxides (REO) play a critical role in enabling high performance and efficiency in gas turbines used for power generation and propulsion. To meet evolving performance constraints, current and next-generation coating architectures employ a wide range of material systems containing larger fractions of REO compared to prior coating technologies. This chapter reviews the application requirements, design considerations and typical architectures for the thermal barrier coatings (TBCs) used to protect metal alloys and the environmental barrier coatings (EBCs) used to protect ceramic composites. It then introduces key materials families based on rare earth aluminates, hafnates, silicates, zirconates and related systems. Finally, the chapter discusses the techno-economic considerations for selection of the material system and REO constituent, and the outlook toward new materials and future coating systems.

With the advent of a clean energy economy, our society is moving away from a fuel-intensive energy system to a material-intensive system that relies heavily on critical materials such as rare earth elements (REEs), according to the international energy agency. However, REE production is currently dominated by a few countries leaving the rest of the world vulnerable to supply risks which hinder clean energy technology development and national security. To mitigate the risks researchers are exploring circular economy (CE) strategies to recover value from end-of-life products that contain REEs. Hard disk drives (HDDs) are identified as a promising feedstock for such CE strategies along with other opportunities from consumer electronics (e.g., smartphones), household appliances (e.g., washers and dryers), medical equipment (e.g., magnetic resonance imaging (MRI) scanners) and electric vehicles (EVs). The value recovery pathways include product reuse, Nd-Fe-B magnet reuse, magnet assembly reuse, magnet remanufacturing and REE recovery. In this chapter, new technologies that support these value recovery pathways are reviewed, focusing on the recent advancements, challenges and opportunities. The economic, environmental and supply chain implications of adopting these technologies are also evaluated for economic and environmental sustainability. Future research is suggested to prioritize reuse strategies over recycling and integrate the novel value recovery processes into the established supply chain to close the material loop.

Europium and yttrium (Y) are critical materials required for light-emitting diode (LED), florescent lamp (FL), cell phone screen and flat panel display production. Nearly, the entire worldwide production of europium (Eu) is sourced as a minor constituent recovered from mining bastnäsite, monazite ore or ion-absorbing clays in China. Ongoing supply risks, environmental legacies from previous operations and the drive toward monetizing end-of-life (EoL) waste streams that otherwise are destined for landfills are the inspirational basis for this chapter that is focused on rare earth element (REE) recycling from lighting phosphors. A recently developed mild acid-leach and reduction-precipitation process is described for high recovery of Eu as europium(II) sulfate (EuSO₄) and coproduction of Y from waste lamp phosphor dust.

In the mining and minerals sector, new development projects are assessed for economic viability using a standard approach whereby resource and reserve data are evaluated alongside cost and revenue estimates. While this universal approach can be applied for any mined commodity, projects in the rare earth element (REE) sector have unique attributes that merit specific attention, most notably including inconsistent product pricing structures and market entry concerns. For example, the REE pricing used in any individual study may vary considerably from others depending on the data source, the year of study, and the extent of separation and refining included in the assessment. Altogether, these issues can create challenges when analyzing reported economic projections at face value or making comparisons between dissimilar projects. Recognizing these nuances, this chapter seeks to provide a set of economic benchmarks for REE development projects using a fixed REE pricing deck and a common evaluation methodology.

Technical and economic data were collected from public disclosures for 42 distinct REE development projects. Of these, 21 were found to be of sufficient maturity to include pro forma cash flow projections suitable for detailed economic analysis. The technical and economic data were then aggregated to identify trends and outliers among the population of development projects. Lastly, these findings were compared against similar economic projections for several unconventional REE resources, including monazite sand, coal refuse, acid mine drainage and seafloor sediments. In summary, the findings show that conventional REE ore deposits vary in grade from approximately 300 ppm to nearly 15% total rare earth oxide (TREO) content; however, the majority of the deposits with viable economic outcomes were between 0.5% and 2% TREO. At the time of their publication, many of these projects reported robust economic outcomes with all 21 showing payback periods (PP) of 7 years or less and net present values (10% discount rate) in the hundreds of millions to billions of dollars. A revised analysis using a lower price deck (i.e., January 2020 market prices) showed less-favorable outcomes, with only 9 of the 21 having a positive calculated gross margin. Similarly, analysis of unconventional resources showed that while the REE resource is vast in most cases (e.g., seafloor sediment and coal refuse), the contained values can be quite low, but still within the range of conventional deposits. Overall, the findings of this assessment further emphasize the need for low cost production and innovative technological advances for both conventional and unconventional resources.

An overview of potential environmental regulations is provided in this section for stakeholders who are concerned with the environmental, health effects and impacts across authorities for rare earth elements (REE) and critical minerals (CM) recovered from both conventional as well as unconventional feedstock resources as mine tailings, abandoned hard rock mining sites, coal and coal by-products and recycling. Regulations for REE and CM recovery facilities will be based on the source material matrix, the type of recovery process (chemical, physical or biological), the surrounding environment in association with the types of potential discharges and storage of hazardous materials located on or at the recovery facilities. It is recommended that any new facility that is being planned for REE and/or CM recovery consult their federal, state, and local environmental regulatory agencies. Early regulatory consultation for new facilities and or for the expansion of existing facilities is recommended prior to and during the permit application process.