How rare are rare earths really?

Rare earth elements, a group of 17 metals, are relatively abundant in the Earth's crust but their extraction is extremely difficult.

Neodymium, one of the rare earth elements that is extremely difficult to mine. Photo: RHJ/Getty — Neodymium, one of the rare earth elements that is extremely difficult to mine. Photo: *RHJ/Getty*

Rare earth elements have many useful properties that make them very popular in the energy and technology industries. This group includes 17 metals, including 15 metallic elements at the bottom of the periodic table, along with 2 elements yttrium and scandium.

The most valuable of these elements are neodymium, praseodymium, terbium and dysprosium, which act as powerful miniature magnets, a key component in electronic devices such as smartphones, electric car batteries and wind turbines. However, the limited supply of rare earths is a major concern for companies and governments producing these modern necessities.

Rare earths aren’t actually that rare. According to a USGS study of the crystalline abundances of various elements (how abundant they are on average in the Earth’s crust), most rare earths are found in about the same quantities as common metals like copper and zinc. “They’re certainly not as rare as metals like silver, gold, and platinum,” says Aaron Noble, a professor at Virginia Tech.

But extracting them from natural sources is extremely difficult. “The problem is they’re not concentrated in one place. There are about 300 milligrams of rare earths in every kilogram of shale across the United States,” says Paul Ziemkiewicz, director of the West Virginia Water Research Institute.

Normally, metals accumulate in the Earth’s crust due to various geological processes, such as lava flows, hydrothermal activity, and mountain building. However, the unusual chemical properties of rare earth elements mean that they do not often accumulate together under these special conditions. Traces of rare earths are scattered across the planet, making their extraction inefficient.

Sometimes, acidic underground environments can slightly increase the amount of rare earth elements in certain locations. But finding these locations is just the first challenge.

In nature, metals exist as mixtures called ores, which contain metal molecules bound to other non-metals (counter-ions) by strong ionic bonds. To obtain pure metals, people have to break these bonds and remove the non-metals. The difficulty of the work depends on the metal and the non-metal they are bound to.

"Copper ore usually comes in the form of sulfides (chemicals made up of sulfur and other elements). You heat the ore to the point where the sulfides escape as a gas and the pure copper falls to the bottom of the reactor. That's a pretty easy extraction process. Some other types, like iron oxide, require additives to release the metal. But separating rare earths is much more complicated," Ziemkiewicz explains.

Rare earth metals have three positive charges and form extremely strong ionic bonds with phosphate counterions, each of which has three negative charges. Therefore, the extraction process must overcome the extremely strong bond between the positive metal and the negative phosphate.

"Rare earth ores are very chemically stable minerals, and it takes a lot of energy and chemical power to break them down. Typically, that process requires extremely low pH, harsh conditions, and extremely high temperatures because the bonds in the ore are incredibly strong," Noble said.

The difficulty in isolating the pure elements has earned them the name “rare earths.” Some experts are researching new methods for recycling and extracting these valuable metals from industrial waste and old electronics to ease the pressure on current supplies. They are also trying to recreate the unique magnetic and electronic properties of rare earths in new compounds, hoping these will become more accessible alternatives. However, there are currently no viable alternatives to rare earths, despite growing demand.

Thu Thao (According to Live Science )

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