The most valuable of these are neodymium, praseodymium, terbium and dysprosium, which are super-strong micromagnets that are essential components of electronics such as smartphones, electric car batteries and wind turbines. However, their limited global supply is a major concern for governments and businesses, as they need these metals to continue manufacturing various types of modern necessities.
But why are rare earth elements so rare?
It turns out they’re actually not that rare. A U.S. Geological Survey study of the “crystalline abundances” of various elements—that is, the amounts available in the average Earth’s crust—found that most rare earths are “of roughly the same order of magnitude as common metals such as copper and zinc.” ”
Aaron Noble, professor and chair of the Department of Mining and Mineral Engineering at Virginia Tech, told Live Science. “They are certainly not as rare as metals like silver, sleep And platinum. ”
connected: Which is rarer, gold or diamonds?
Location and relative abundance of mineable rare earth elements around the world. 2020 USGS data. (Image credit: Visual Capitalist/Science Photo Library via Getty Images)
Although these elements are common, extracting them from natural sources is very difficult.
“‘Troubled Earth’ would have been a better name,”
Paul Zimkiewiczthe director of the West Virginia Water Institute told Live Science. “The problem is, they’re not concentrated in one place. The rare earth content in all shale in the United States is about 300 milligrams per kilogram (0.005 ounces per pound). If you dig a hole in your backyard, you’ll find this.”
Typically, metals are concentrated within the Earth’s crust due to various geological processes such as lava flows, hydrothermal activity, and mountain building. However, the unusual chemistry of rare earth elements means these metals don’t usually clump together under these special conditions. As a result, traces of these elements are scattered throughout the Earth, making mining these materials particularly inefficient.
Sometimes, extremely acidic conditions underground can slightly increase the amount of rare earth elements in some areas. But finding these elusive rich sites is only the first challenge.
In nature, metals occur in the form of compounds called ores, which are composed of metal particles linked by strong ionic bonds to other non-metallic substances called counterions. To obtain a pure metal, these bonds must be broken and the counterpart removed – but the difficulty of this separation depends on the metal and counterpart involved.
All types of metals may be present in the ore, not just rare earth elements. For example, copper and iron can also form ores.
“Copper ore usually exists in the form of sulfide. The ore is heated to a point where the sulfide is released in the form of a gas, and pure copper falls from the bottom of the reaction vessel. It’s easy. There’s extraction,” Zimkiewicz explains Tao. “Others, such as iron oxide, require additives to release the metal. But separating rare earths is more complicated.”
Rare earth metals naturally have three positive charges and form extremely strong ionic bonds with phosphate counterions, each of which has three negative charges. The extraction process therefore has to overcome the very strong attraction between the positive metal and the negative phosphate – no easy task.
“This is a very long and complex supply chain for pure metals,” Noble said. “Rare earth ores are very chemically stable minerals – you have to invest a lot of energy and chemical intensity to break them down. Typically, the process uses very low pH, very harsh conditions and very high temperatures.” Because it will The bonds that hold the minerals together are very strong. ”
The difficulty of extracting pure elements is what gives rare earth elements their name. Some researchers are working on new ways to recycle and extract these valuable metals from old electronics and industrial waste to relieve pressure on current supplies; others are trying to recreate the unusual magnetic and electronic properties in new compounds to Providing alternatives to these elusive metals and converting them into more readily available man-made compounds that behave similarly to rare earth elements. .