Searching for Rare Earth Elements from space and how minerals made in the lab play a key role

If you are looking for a powerful magnet, you probably leave the hardware store with something called a neodymium magnet.

Neodymium is a chemical element with exceptional magnetic properties. It belongs to a group of elements collectively known as the rare earth elements, so your magnet may also be called a rare earth magnet.

If you are a manufacturer of a giant wind turbine designed to operate at sea for many years with minimal maintenance, you want to put the best magnets money can buy in the generator. The generator is the part of the turbine which turns the rotation of the blades into electricity. The most reliable (and quiet) turbines have no gearbox, but that only works if you use rare earth magnets in the generator. A modern turbine uses 200 kg of neodymium for every megawatt of power.

Magnets containing neodymium and other rare earth elements are used in electric vehicle motors. They also play a crucial role in LED lights and lots of electronics.

The rare earth elements are genuinely some of the ‘super-elements’ driving modern society and the energy transition.

Dependency on China

But there is a snag.

The rare earth elements in these magnets are almost certainly mined and refined in China. The International Energy Agency estimates that 60% of the rare earth elements ores are mined in China, and nearly 90% are refined there. As a result, the magnet itself is almost certainly produced in China, too.

This dependency on a single country for material so essential for the energy transition makes the European Commission and many national governments around the world very nervous.

The US government has decreed that no Chinese rare earth magnets may be used in any of its military applications.

The game-changer of remote sensing

They are called critical raw materials because of the enormous importance of rare earth elements for modern society and because of concerns about the security of supply.

So, exploration geologists worldwide are looking for new sources of these valuable raw materials.

And increasingly, remote sensing is seen as a game-changer in the search for rare earth elements.

Because, as it turns out, remote sensing using multispectral or hyperspectral sensors is remarkably well suited for detecting rare earth elements in rocks and minerals.

The unusual arrangements of the electrons in these chemical elements give them powerful magnetic properties and absorb light at distinct wavelengths - for instance, in the visible light and in the shortwave infrared part of the spectrum.

So, in the sunlight bounced off rocks containing rare earth elements, certain wavelengths are missing, which are tell-tale signs of rare earth elements in these rocks. And satellites can detect these missing wavelengths!

New research at ITC

Thanks to our new research by the Faculty of Geoinformation Science and Earth Observation of the University of Twente, published in the journal Physics and Chemistry of Minerals, these diagnostic wavelengths at which different rare earth elements absorb light are now better known and understood than ever before.

We took the original approach to synthesize two common ore minerals that contain rare earth elements, monazite and xenotime, in the lab. With this approach, we can carefully control the chemical composition of these minerals.

For instance, we made a series of monazite minerals, each with only one rare earth element at a time. We determined at which wavelengths this element absorbs light. In nature, many rare earth elements occur together in minerals, resulting in a complex array of absorptions that could not be easily linked to individual rare earth elements before.

We also looked at how the nature and arrangements of other elements around the rare earth element in the crystal lattice of these minerals slightly changed the wavelengths of these diagnostic absorptions.

This will help us to determine not only which rare earth elements are present in a rock but also which minerals they are present in. And all this can be done from space!

Application of new knowledge

This new knowledge was already successfully applied in an exciting remote sensing study of a rare earth mine in the US by a team from Potsdam University, using the data from the new, state-of-the-art German EnMAP hyperspectral satellite.

This is just the beginning, and satellites will be at the forefront of mineral exploration for new rare earth element resources.