Dysprosium Supply

One shining example of a scarce resource in need of conservation is the Rare Earth Elements (REE) series generally, and Neodymium, Nd, and Dysprosium, Dy, in particular. Nd is described as hard and not very malleable and ductile and Dy is very malleable. Both have a silvery metallic luster and similar chemistries forming +3 cation as the most stable cation. The REEs are often divided in a funny way. There are the Lanthanides which can be further subdivided into two subgroups – the light REEs from Lanthanum to Europium and the heavy REEs from Gadolinium to Lutetium. Of the lanthanides, heavy REE deposits are more scarce, but of the heavy group Dy is the most abundant.

Promethium is highly radioactive Lanthanide with a half-life of 17.7 years for the longest lived isotope, ¹⁴⁵Pm. Interestingly, the mode of decay for this isotope is electron capture, sometimes called K-Capture. Promethium has only a transitory existence due to its radioactivity. The entire group of REEs share the ability to form +3 cations. This increases the difficulty of isolating pure elements from an ore since most ores contain multiple REEs. Worse, the +3 Lanthanides also have similar ionic radii allowing for them to substitute with each other in minerals.

In the other subgroup are Scandium and Yttrium- sometimes called the Scandium group. In the periodic table all of the REEs are transition metals in Group 3.

For clarity, the image below shows a yellow vertical column of two elements, scandium and yttrium. They are members of the REE group. The yellow row of elements below are the Lanthanide elements. All together they make up the REEs. The Lanthanide elements differ from the other two REEs in that they have f-orbitals with valence electrons.

We’ll go into valence electrons a bit because most of the REEs have f-orbitals.

Chemistry is about what valence electrons do. These are the electrons that interact with the world around the atom or molecule. All electrons in an atom or molecule spend their time in regions of space called orbitals. Electrons in the valence level can be taken away or shared. If there is an empty space in the valence level, an electron can be dropped in. Valence electrons form chemical bonds. These electrons are chemically reactive because they are furthest from the nucleus and feel the least nuclear attraction. But their reactivity mostly disappears if the valence orbitals are full. Inert gases are inert because their valence orbitals are full.

Electrons spend their time in specially shaped regions of space around atoms and molecules. We do not need to know where an electron is exactly at any given moment. The orbital shapes define where electrons spend 95 % of their time. Orbitals do not have sharp edges. They taper off into space. The image below is a more realistic representation of where electrons can be found.

It turns out that we can describe the space electrons occupy if we apply the mathematics of a spherical harmonic series. The image below shows 4 levels of the series. The shapes define the space that electrons occupy around an atom. Each row represents a group of individual orbitals. Top to bottom, they are labeled s, p, d and f. The orbitals are filled with electrons theoretically in order from top to bottom rows as you move up the periodic table by atomic number, with each orbital holding as many as 2 electrons. Remember, orbitals are not physical objects. Each of them define a region of space in which one or two electrons spend their time. Also, there is some nuance in the energy levels of the orbitals. No matter though for this post.

Below is a chart showing atomic orbitals oriented in an xyz coordinate system. Interactions of orbitals between atoms or molecules very much depend on how they are oriented as they contact.

The common elements we are familiar with have s, p and d valence orbitals around the nucleus. As we increase the atomic number of the elements we drop down the rows of orbitals on the graphic and the periodic table, the valence electrons get further away from the nucleus. The consequence is that the energy needed by the first valence electron to escape becomes smaller.

We live in a time of permanent magnets with extraordinarily high magnetic field strengths. They’re called rare earth magnets and two REEs stand out in particular in this application- Neodymium (Nd) and Dysprosium (Dy). Nd is the primary REE in this type of magnet, but It turns out that up to 6 % of Nd can be replaced with Dy to increase coercivity and increase resistance to demagnetization. This is important for heavy duty magnet applications like windmills and electric cars. It is estimated that replacement of Nd with Dy in REE magnets amounts to ~100 grams of Dy per car. Based on Toyota’s planned output 3.5 million battery operated electric vehicles per year by 2030, the current reserves Dy would soon be exhausted.

Rare earth magnets are generally comprised of 3 elements; Neodymium, Nd; Iron, Fe; and Boron, B, proportioned according to the formula Nd₂Fe₁₄B. Dy is an optional component of these magnets.

So, obviously Dy is a highly desirable metal for efficient use of permanent RE magnets. Even among the REEs, Dy is a minor element. There are no known minerals having Dy as the major REE. The crustal abundance of Dy is 0.3 ppm and the recycle rate is <10%. The major reserve holders are China, Russia, and the USA. Incidentally, for some years now China has been disinclined to supply REE ore in favor of value added REE finished goods. This is in contrast to their buying copper ore from Chile or Peru in order to capture lower copper costs by doing their own refining. They know what they are doing.

Plainly, much is yet to be done in regard to putting a recycle loop in place for REEs in products. This is especially true for dysprosium. So, do we wait for the free market to respond when the situation is dire and the bulk of the REEs are already consigned to landfills around the world?

Note: For the sake of keeping the post light and airy, I’ve made some generalizations above. Of course there are exceptions and nuances. There always are.