What are the rare earth elements?

The entire basis of my exhibit here in Germany is the rare earth elements. But there is always the question: what exactly are the rare earth elements? (This is a long post; you can scroll to the bottom for the tl;dr if you’d like).

The rare earth elements (REE) are 17 elements on the periodic table, usually shown at the bottom, the lanthanide series, plus scandium and yttrium from the main periodic table.

periodic-system-ree

These 17 elements can further be divided into two distinct categories: the light REE and the heavy REE. The light REE are the elements with numbers 21, 57 through 64; these are known as the cerium group. The heavy REE are elements 39, 65 through 70 and are known as the yttrium group.

There are some misleading terms out there. First, “rare earth metal” is used in place of the rare earth elements, but they are not the same things. When someone uses the term rare earth metal, they are usually including elements like gold, silver, or platinum, or minerals such as coltan. Though they are all considered rare earth resources, only the 17 elements listed above are considered the rare earth elements. (There is another argument: there are really only 15 rare earth elements, the 15 found in the lanthanide series. Scandium and yttrium do not belong to this group. For reference, from here on out I am going to refer to all 17 elements when I say “the rare earth elements.”)

Finally, the biggest misleading term: none of these elements are really rare except 61, promethium. Many of them are more common than gold or platinum. Cerium is about as common as copper in the world. Due to their geologic and chemical structures, getting enough of them in the same place to be economically viable is difficult.  Think about baking: if you add a teaspoon of cinnamon to a kilo of flour, you really can’t separate the two of them again. You know the cinnamon is there, but getting it out is extremely difficult.

Bear with me through the chemistry for a second: the lanthanide series on the bottom has what’s known as “lanthanide contraction,” and this affects why the REE are found where they are. Usually, an increase in the atomic number results in an increase in atomic radii; with the REE this is not the case. Each larger atom in the list has a smaller radius then the ones before it, which also helps increase the weight density of the atom. This is caused by problems with the outer electron shell, 4f. (This all gets very technical very quickly. I encourage you to look it up on Wikipedia for a better explanation). Scandium follows the same pattern, as does yttrium.

In a nutshell: The REE like to hang together and are often found either grouped by the light or heavy REE in the ground.

This brings us to the actual question: so what?

The REE are needed in EVERY form of modern day life. They act a lot like vitamins, helping other elements work more efficiently, faster, and stronger. Without them, your screens wouldn’t have beautiful reds (europium) or greens (terbium) when you binge-watch Netflix. Many light bulbs now contain a REE of some kind. Your cellphone has at least 7 of them (the violet ones):

Source: www.compoundchem.com
Source: http://www.compoundchem.com

You find the REE in every type of green energy too. The Prius has over 10 kilograms of lanthanum in it’s battery and a kilogram of neodymium in the motor. A large windmill has over 500 kilograms (so over 1000 pounds) of REE.

© Eli Patten 2016, all rights reserved. Used with permission. There are over 40 pounds of rare earth element in this picture in the Priuses alone!
© Eli Patten 2016, all rights reserved. Used with permission.
There are over 40 kilograms of rare earth element in this picture. And that’s just the Prius-es!

REE are also used a lot in medical purposes, like xray, PET scans, and mobile imaging. The four harddrives that I have backing up my copies of this blog all use REE in the magnets in the harddrive. Without the REE, your MP3 player would be more like a walkman, and there wouldn’t be anything like the iPod Nano. The REE currently power our daily lives.

tl;dr The REE are 17 elements on the periodic table that like to hang out together. They are what let us have small harddrives and show you greens and reds when you binge watch Netflix. They aren’t really rare, just hard to find in mineable quantities. Without them, we wouldn’t have electric cars or those huge windmills, not to mention any iProduct.

Next up: What do the REE look like?

2 thoughts on “What are the rare earth elements?

    1. Hi! That is a great question.

      They are difficult to mine, but there are a lot of them. And we have a lot stockpiled. There were also a lot of stockpiles involved. We actually have a huge amount of rare earths; estimates say that at current usage, we still have enough for 500 years, possibly longer.

      Like

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