Today's KNOWLEDGE Share : High Pure Rare Earth Elements

Today's KNOWLEDGE Share

Highly pure rare-earth elements are NOT essential for the production of Nd-Fe-B (neodymium-iron-boron) magnets. Nd-Fe-B magnets can be made from mixtures of rare-earth elements (REE) rather than highly pure metals of the individual REE. This possibility is often overlooked, but it could lead to much cheaper and more sustainable Nd-Fe-B magnets.

REE mixtures can be separated into individual REE with a purity of more than 99.9% by solvent extraction (SX). For full separation of a mixture of all REE, more than 1000 SX stages are required. This makes REE separation an expensive and tedious process.

While highly pure REE oxides are required for luminescent materials such as lamp phosphors or laser crystals, this is not the case for REE permanent magnets that are essential for electric vehicles, wind turbines, and military applications.

We do not need 99.9% pure neodymium for high-quality Nd-Fe-B magnets. Nd₂Fe₁₄B (the main phase in Nd-Fe-B magnets) and its praseodymium analogue Pr₂Fe₁₄B, as well as mixtures of Nd₂Fe₁₄B and Pr₂Fe₁₄B, can be used for Nd-Fe-B magnets without experiencing any significant deterioration in magnetic properties. Therefore, the neodymium does not need to be more than 95% pure. It is even possible to prepare strong permanent magnets from mischmetal, a mixture of non-separated rare earths, using the naturally occurring ratio of these elements found in their ores. Only the samarium must be removed.

Dysprosium and terbium are often added to Nd-Fe-B magnets to help maintain the magnetic properties of the magnets at higher temperatures. This makes the magnets more reliable and efficient in high-temperature environments, such as in electric vehicle motors. It is very difficult to separate these elements, but they do not need to be separated for use in magnets. They can be added to the magnet alloy as a dysprosium-terbium mixture.

I was not aware of this myself until we analyzed different magnets used in cars at SOLVOMET R&I Centre. To illustrate this, have a look at the following chemical composition of a REE magnet from a power steering motor of a car:

Neodymium: 20.9 wt%

Dysprosium: 3.8 wt%

Praseodymium: 4.2 wt%

Terbium: 0.6 wt%

Gadolinium: 0.2 wt%

(Total REE content: 29.7 wt%)

This raises the question: Why are we spending so much effort on the over-purification of REE for permanent magnet production? This is something to reflect upon.

Credit picture: Shutterstock

source: Koen Binnemans

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