Rare Earth Elements: Abundant Yet Difficult to Extract
Rare earth elements (REEs) comprise 17 metals that are relatively abundant in the Earth’s crust, but their extraction is extremely challenging. These elements possess many useful properties, making them highly sought after in the energy and technology sectors. This group includes 15 metallic elements at the end of the periodic table, along with two elements, yttrium and scandium.
The most valuable elements among them are neodymium, praseodymium, terbium, and dysprosium, which function as ultra-strong magnets and are crucial components in electronic devices such as smartphones, electric vehicle batteries, and wind turbines. However, the limited supply of rare earth elements poses a significant concern for companies and governments producing essential modern-day products.
Neodymium, a rare earth element that is extremely difficult to extract. (Photo: RHJ/Getty).
Rare earth elements are not actually that rare. According to research from the United States Geological Survey (USGS) on the abundance of various elements (the average availability in the Earth’s crust), most rare earths have similar quantities to common metals like copper and zinc. “They are certainly not as rare as metals like silver, gold, or platinum,” said Aaron Noble, a professor at Virginia Polytechnic Institute and State University.
However, extracting them from natural sources is extremely difficult. “The issue is that they are not concentrated in one location. There are about 300 milligrams of rare earths in each kilogram of shale rock throughout the United States,” Paul Ziemkiewicz, director of the West Virginia Water Research Institute, stated.
Typically, metals concentrate in the Earth’s crust due to various geological processes, such as magma flow, hydrothermal activity, and mountain formation. However, the unusual chemical properties of rare earth elements often prevent them from concentrating together under these specific conditions. Traces of rare earth elements are scattered across the planet, making their extraction inefficient.
Sometimes, acid-rich underground environments can slightly increase the concentration of rare earth elements at certain sites. However, finding these locations is just the first challenge.
In nature, metals exist in a mixture known as ore, which contains metal molecules bonded with non-metal elements (counter-ions) through strong ionic bonds. To obtain pure metals, these bonds must be broken, and the non-metals removed. The difficulty of this process depends on the metal and the non-metal it is bonded with.
“Copper ore often appears as sulfide (a chemical compound consisting of sulfur and another element). You heat the ore to the point where the sulfide escapes as gas, and pure copper falls to the bottom of the reactor. That is a relatively easy extraction process. Other types, such as iron oxide, require additives to release the metal. But separating rare earth elements is much more complex,” Ziemkiewicz explained.
Rare earth metals have three positive charges and form extremely strong ionic bonds with phosphate counter-ions, each having three negative charges. As a result, the extraction process must overcome the exceptionally strong bond between the positive metals and negative phosphates.
“Rare earth ores are very chemically stable minerals, requiring a lot of energy and chemical strength to break them down. Typically, this process demands extremely low pH, harsh conditions, and very high temperatures because the bonds in the ore are incredibly strong,” Noble noted.
The challenges in extracting pure elements have led to the term “rare earth.” Some experts are researching new methods to recycle and extract these valuable metals from industrial waste and old electronics to alleviate pressure on current supplies. They are also attempting to recreate the unique magnetic and electronic properties of rare earths in new compounds, hoping these new compounds will become more accessible alternatives. However, currently, there are no effective alternative sources for rare earth elements, despite the rising demand.
