Rare earth elements are a key strategic concern for most nations today. This group of elements is a critical input for the technology that drives modern life, and as a result, securing supply is a core strategic focus for both governments and businesses.
To understand why, it helps to look at what rare earths actually are — and why they’re often misunderstood as being scarce.
What are Rare Earths?
Rare Earth Elements (REE) are defined by the USGS as a “group of 17 elements composed of scandium, yttrium, and the lanthanides”[1] (Lanthanum, Cerium, Praseodymium, Neodymium, Promethium, Samarium, Europium, Gadolinium, Terbium, Dysprosium, Holmium, Erbium, Thulium, Ytterbium, Lutetium). This group of elements possess unique properties that have made them useful for a range of applications.
REEs have enabled key technological advancements, leading to improvements in magnets, computer hard drives, and other ever-shrinking technology we rely on every day. Additionally, REEs have supported advances in materials utilized by engineers for defense and aerospace applications.[2]
Names and chemical formulas of some important REE-bearing minerals associated with REE deposits are shown in the table below[3]
| Mineral | Formula |
| Allanite | (Y,Ln,Ca)2(Al,Fe3+)3(SiO4)3(OH) |
| Apatite | (Ca,Ln)5(PO4)3(F,Cl,OH) |
| Bastnaesite | (Ln,Y) (CO3)F |
| Eudialyte | Na4(Ca,Ln)2(Fe2+,Mn2+,Y)ZrSi8O22(OH,Cl)2 |
| Fergusonite | (Ln,Y)NbO4 |
| Gittinsite | CaZrSi2O7 |
| Iimoriite | Y2(SiO4) (CO3) |
| Kainosite | Ca2(Y,Ln)2Si4O12(CO3)·H2O |
| Loparite | (Ln,Na,Ca) (Ti,Nb)O3 |
| Monazite | (Ln,Th)PO4 |
| Mosandrite | (Na,Ca)3Ca3Ln (Ti,Nb,Zr) (Si2O7)2(O,OH,F)4 |
| Parisite | Ca (Ln)2(CO3)3F2 |
| Pyrochlore | (Ca,Na,Ln)2Nb2O6(OH,F) |
| Rinkite (rinkolite) | (Ca,Ln)4Na(Na,Ca)2Ti(Si2O7)2(O,F)2 |
| Steenstrupine | Na14Ln6Mn2Fe2(Zr,Th) (Si6O18)2(PO4)7·3H2O |
| Synchysite | Ca (Ln) (CO3)2F |
| Xenotime | YPO4 |
| Zircon | (Zr,Ln)SiO4 |
How Rare Are They?
Despite their name, rare earth elements are not especially rare.
If you consider the USGS annually compiled data on Rare Earth statistics, you can see that many of the elements in the Rare Earth group are quite abundant. For example, cerium is 25th on the list of 78 common elements that are found in the Earth’s crust[4]. The perception of rarity stems from the challenging and expensive process of separating the REEs from the ore. The elements tend to occur in compounds dispersed throughout a rock and are often found with several REEs in one area, not concentrated in large mineral compounds as is common for many other commoditized elements. This means that they require expensive and challenging processes to separate and purify them sufficiently to move through the supply chain[5]. Additionally, deposits of these elements occur around the globe, with only a few REEs present at any one extraction site.
It is the complexity and cost of extraction that drives the perception of rarity for REEs. But despite the actual abundance, the supply is still finite. Precise measurement is essential for site evaluation and for the raw materials and finished products of each REE processing step to ensure that all material is accurately accounted for.
Measuring REE – An Essential but Complicated Task
Handheld XRF is a common tool for mapping prospective sites. This non-destructive technique analyzes the elemental composition of geological samples using the characteristic fluorescent x-rays for each element. The accuracy of this technique is maximized by utilizing calibration sets. These calibration sets typically include a range of ore or geological powder CRMs pre-loaded into XRF sample cups for quick and easy use in the field. Accurate mapping helps control costs by ensuring that the samples sent to the lab for detailed and defensible analysis represent the most promising locations.
Notably, handheld XRF also plays a role during the recycling of goods containing REEs. This analysis is especially useful to identify toxic metals that are present alongside REEs in items like circuit boards to limit their entry into recycling streams. Unfortunately, only limited quantities of REEs are recovered through recycling today[6].
When it comes to processing REEs, numerous steps, including chemical flotation, acid leach, heat treatment, and solvent extraction, are required to separate, concentrate, and purify the elements. These numerous steps are necessary due to the similar chemical properties of the rare earth elements which can easily substitute for each other in mineral compounds. This same feature means that the chemical analysis needed to confirm the results of processing steps can be challenging as well.
Beyond field analysis, laboratory techniques such as ICP-MS provide the precision needed during processing steps. This analytical technique offers a high level of sensitivity, multi-element capability, and limited interferences enabling analysts to overcome the complexities of testing REEs. But similar to hand-held XRF, calibration is key. ICP-MS is a comparative technique that relies on the quality of the standards deployed during method set-up to achieve peak accuracy. No compromise can be made on standard selection - from tuning solutions to calibration standards – certified reference materials are the best choice.
When discussing analysis, it is important to also consider sample preparation. While some techniques such as LIBS, handheld XRF or LA-ICP-MS can be performed with little to no preparation of sample, most of the commonly used lab techniques require that the sample be processed into a form suitable for analysis. For higher quality, lab-based XRF analysis, samples must be pressed into pellets or paired with a suitable flux and prepared by fusion. On the other hand, for samples to be analyzed by ICP-OES, they must first be fully digested into a liquid form. Regardless of the sample preparation process, laboratory best practices must be deployed to ensure no contamination is introduced to the sample through the additional handling. These best practices include using high-quality reagents or acids for any processing steps.
The special physical and chemical properties of REEs, which have made them a critical part of our modern high-tech, lives also add to complexity of the steps involved in mining and processing them. Precision across every stage, from mining to finished materials, depends on the use of high-purity reagents for extraction and certified reference materials for calibration in analytical instruments such as XRF and ICP.
AnalytiChem provides trusted solutions for every stage of rare earth analysis - from exploration to quality control. Get in touch with our team to learn how we can support your workflow with precision and confidence.
[1] Rare Earths Statistics and Information | U.S. Geological Survey (usgs.gov)
[2] Rare Earths Explained - Milken Institute Review (milkenreview.org)
[3] V. Balaram, Rare earth elements: A review of applications, occurrence, exploration, analysis, recycling, and environmental impact, Geoscience Frontiers, Volume 10, Issue 4, 2019, Pages 1285-1303, ISSN 1674-9871, https://doi.org/10.1016/j.gsf.2018.12.005.
[4] Rare Earths Statistics and Information | U.S. Geological Survey (usgs.gov)
[5] Rare Earths Explained - Milken Institute Review (milkenreview.org)