Rare earths are indispensable raw materials with a high global demand. They are essential for the energy transition, as they are used for manufacturing electric motors, rechargeable batteries and wind turbines. The mining involves extensive use of chemicals and is therefore harmful to the environment. This makes it all the more important to use and recycle the rare earths that are already available in a way that conserves resources. Reuse is also the goal of Heraeus Remloy: We use a new process to recycle permanent magnets made of neodymium.
Rare earths - important metals for future technologies
The Rare Earths - What are they?
Rare earths are the 17 elements of the lanthanides, as well as yttrium and scandium. All of these chemical elements are metals. By the way, rare earths are not as rare as the name suggests: neodymium, for example, occurs more frequently in the earth's crust than lead, copper or gold. The metals owe their name to the time of their discovery. They were explored as oxide compounds, formerly called earths, in rare minerals. Neodymium was finally discovered as an independent element at the end of the 19th century and was first produced in its pure form in 1925.
Rare earths play a key role in our everyday lives: smartphones, laptops, electric cars, power tools all need rare earths. Neodymium is required for permanent magnets in electric motors and hard drives.
Frequent metals ─ rare occurrences
Depots for rare earths are limited, however. Many of the metals are only extracted as a byproduct of other ore mining operations. This results in only small quantities in each case. In 2020, global mining production of rare earth oxide was 214,000 metric tons. Nearly 70 percent of this mining and refining comes from China, and one-third solely from the Bayan Obo mine in Inner Mongolia.
There are other depots of rare earth metals in North America, Australia, Greenland, Russia and even Germany. However, the depots are too small or unexploited for mining to be economically profitable. Due to China's dominant market position, the European Commission currently sees rare earths as raw materials with the highest supply risk. The German Parliament's Scientific Service has also considered the importance of rare earths and consolidated relevant facts in a document ("Rare earths as an important resource").
How to mine rare earths?
Rare earths are mainly mined in industrial opencast mines. They occur as oxides. In Bayan Obo, for example, mining of rare earths takes place as a byproduct of iron ore production. After extraction, the ore is crushed and milled. Optional magnetic separation is followed by multi-stage flotation to produce a rare earth mineral concentrate such as bastnäsite or monazite.
The concentrate is then dried and roasted with the addition of sulfuric acid and digested. Thereafter, the concentrate is processed with a caustic solution. The steps differ depending on the type of mining and the composition of the concentrates. Finally, the various rare earths are separated with organic solvents. Energy-intensive fused-salt electrolysis is required to extract metallic neodymium from the oxide. Typically, one kilogram of neodymium can be extracted from 200 kilograms of raw ore.
The problems of rare earth mining
The mining of rare earths is energy-intensive, complex and very harmful to the environment because many chemicals are used. Depending on the mining method, soil layers containing rare earths have to be directly leached and removed over the whole area. This results in massive impacts on the environment. In addition, the extraction process requires a large amount of water. The production of one kilogram of rare earth oxides requires an average of 2,300 liters of water. Rare earths are also contaminated with radionuclides, especially uranium and thorium. As a result, mining residues are radioactively contaminated, depending on the type of ore deposit. Modern processes that have less environmental impact are currently rarely used, which makes recycling all the more important.
Rare earth magnets
Rare earth magnets are permanent magnets made of rare earth metals. Compared to traditional magnets, rare-earth magnets have high magnetic remanence flux density and high magnetic coercivity.
One of the most industrially used permanent magnets is made of neodymium-iron-boron (Nd2Fe14B1). These magnets are characterized by very high remanence flux densities, coercive field strengths and energy densities. Neodymium-iron-boron magnets are also especially strong and can therefore have a small form factor. This makes them the perfect choice for applications where space plays a major role, such as in hard drives or hi-fi loudspeakers.
How rare earth magnets are extracted?
Permanent magnets are often pressed into a mold as a crystalline powder. Afterwards, the magnets are sintered, that means heated under pressure, to bond the different base materials. This is followed by magnetization with an external magnetic field. The permanent magnets orient themselves to this magnetic field and thus obtain their magnetic properties.
Read more about the neodymium-iron-boron materials from Heraeus