More abundant than copper and lead, the 17 rare earth elements are by no means scarce. That’s why extracting and refining them is so expensive and polluting.
The so-called rare earths they hide a curious geological and industrial paradox. In fact, hearing the name one would tend to think of scarce and, indeed, rare elements. But that’s not exactly the case.
What are rare earths
The name given to 17 chemical elements that make up the rare earths was given to them at the end of the eighteenth century and in the nineteenth century, when the first chemists isolated these elements from uncommon minerals in Scandinavia, calling them “earths” (an archaic term for oxides) and “rare”.
Their employment has become increasingly essential over the last few decades, especially in the hi-tech sector.
In fact, they are present in smartphones, LED screens, hard drives, speakers and headphones. Some of these elements, such as europium, terbium and yttrium, create the bright colors of displays, while erbium is used to amplify signals in networks in optical fiber.
Rare earths are also essential for producing i permanent magnets very high performance used in electric car engines and wind turbine generators.
Without forgetting their use in missile guidance systems, radars, night vision goggles, high-power lasers and components for satellites and fighters.
The availability in the earth’s crust
The paradox of rare earths However, it lies in the fact that they are not at all scarce on the earth’s crust. Indeed, these 17 chemical elements they are often present in larger quantities than common metals (such as copper, lead or gold).
Let’s take for example the Ceriumthe most abundant of the rare earths, it is present in the earth’s crust in quantities comparable to those of copper or zinc. Also the Neodymium and the Lanthanum, they are about three times more abundant than a common metal such as lead.
Of course, rare earths are not all created equal in terms of availability. They are usually divided into “light” (more common) and “heavy” (more scarce).
Take for example the Thulium and the Lutetiumthe two most scarce rare earths, with an average concentration in the earth’s crust of just 0.5 and 0.8 ppm (parts per million), they are however much more abundant than gold, approximately 200 and 120 times more abundant respectively.
Because it is difficult to extract and refine them
The real criticality lies not in natural availability, but in geological distribution and refining.
Rare earths are almost never found in concentrated deposits, but rather dispersed in very small quantities. The extraction process therefore requires the fragmentation of large volumes of rock to obtain a relatively small quantity of useful material.
Once the mineral has been extracted, the most critical phase is the separation of the different elements: rare earths, in fact, are chemically very similar to each other and tend to always appear mixed.
Separating them requires the use of large quantities of acids and organic solventsthrough repeated and complex processes that make this phase one of the most wasteful and polluting of the entire supply chain.
To the technical difficulty, therefore, is added the economic one, with the need for sophisticated systems and chemical reagents which profoundly affects the sustainability of the process.
The environmental impact
In addition to being expensive, refining has a huge environmental impact. The conventional method is based on sulfuric acid cooking, multi-step leaching and solvent extractiona sequence that generates toxic waste streams and radioactive waste.
According to a Harvard analysis, for every ton of rare earths produced, conventional processing generates approximately 2,000 tons of toxic waste.
They add to this high energy consumption and the use of aggressive chemicals, which make refining one of the most impactful phases of all.
The management of this waste, often radioactive due to the presence of thorium and uranium in the starting rocks, represents a further burden. More than their scarcity, therefore, the problem of rare earths is of an industrial and environmental nature.
