Rare Earths: Why, Where, How?

The enigmatic materials known as rare earths allow the manufacture of some of the most economically and strategically valuable materials of the 21st century. In this brief essay, I aim to understand what they are, why they behave the way they do, how their deposit locations are influenced by these properties, and anticipate some areas of future study.

First, the necessary background. The term “rare” in “rare earths” refers not to their abundance, but to their earliest industrial application – glass colouring. “Rare” in this 19th-century sense meant “extraordinary”, “astonishing”. In fact, some rare earths are far more abundant than gold, silver, and platinum. “Earths” comes from an equally-antiquated usage, meant to refer not to varieties of difficult-to-find muds but rather the metal oxides from which “rare” elements could be extracted.

Image result for rare earth element abundancesAs this table should make clear, rare earth elements (in blue) are generally orders of magnitude over gold or platinum. It should also highlight a property that will start to establish why this particular group of elements stands out. As you can see, the abundance of an element is related to its atomic number. Adjacent elements in the periodic table can have very different abundancies in practice, because of what the atomic number actually means. It’s the number of protons in the atom’s nucleus, and in an uncharged atom, that’s the same as the number of electrons. As atomic numbers increase, electrons can’t all fit at the same distance from the nucleus, especially as it’s now growing larger and more positively charged. As a result, some electrons might be closer to the nucleus and more tightly held by its positive charge, whereas others will be further away and can easily absorb or lose energy.

So why are the abundances of rare-earth elements so similar? Because at this point in the periodic table, as atomic nuclei grow larger and more positively charged, the additional electrons that are counterbalancing their charge are actually quite far off from the nucleus. The inner electronic configuration of the element is quite stable, like a noble gas. The outermost electrons tend to lock into “pairs” in various energy levels. And so, as we’d expect, there is a consistency in the physical and chemical properties of rare earths, except when there is an additional electron that can’t form a pair and tweaks the chemical properties a bit.

This electronic configuration, providing for loose electrons as well as similar physical and chemical properties, drive many applications of rare earths today. About 60% of global rare earth consumption today is driven by their use as catalysts, in alloys, and in magnets. Their applications are summarised in this visual from Nicolas Vogel’s 2011 thesis.

It is in battery alloys and magnets that rare earth elements will find their most valuable applications over the next century. Though, as mentioned, these elements are hardly rare, they are also not often found in economically viable deposits. They form a variety of compounds, from silicates, carbonates, oxides, phosphates, borates, halides, and sulphates – all of which in turn have their own distinct geochemical properties and can be found in various proportions in different kinds of rock based on its formation conditions.

The abundance of rare-earth chondrites (the remains of ancient asteroids) in various clays can be seen in this figure. The Bayan Obo fields of Inner Mongolia, controlled by China, are highly economically viable because of the amount of light rare earth elements that can be processed from the clay. This monopoly is so lucrative that China alone produces and stores more rare earths than most other countries combined. As US-China geopolitical rivalry enters more sectors of the global supply chain, supply-side shocks to the system – intended or unintended – cannot be ruled out.

There is one final layer of complexity to add to this puzzle: sustainability. The extraction and refining of rare earths is expensive and polluting, and up to this point, the costs of the exploration of new nodes – or the costs of keeping up with Chinese pollution standards – have proved prohibitive. Supply from China has, until recently, been taken for granted, but this is a situation that is likely to change in the future,

Given all these questions, India needs to be thinking about the following aspects of the problem.

  1. Is it in India’s national interest to be directly involved in the sale/supply/processing of rare earth elements or their manufactures?
  2. What are the risks, if any, posed by its current stance? What imports/exports/economic sectors could be on the line?
  3. Are there likely to be major changes to this risk/benefit calculation in the coming decades – for ex., will new technology allow efficient recycling of the elements?
  4. What should India’s rare earth strategy look like?
  5. What benefits could be unlocked by a foray into the geopolitics of high-tech manufactures? Should India be a direct player in this game, and if so, how?