Rare earth elements, often referred to as rare earth minerals or rare earth metals, are critical in a number of areas of modern technology including electric vehicles, green energy generation, electronics, military, aerospace, and healthcare.
If you are thinking of investing in rare earth minerals this article explains the mining process and how they are refined. Mining rare earths is expensive and it takes many years to establish new sources.
What are rare earth elements?
In total there are 17 rare earth elements. The table below lists all 17, including their chemical symbols and atomic numbers:
|
Rare earth metal |
Chemical symbol |
Atomic number |
| Scandium | Sc | 21 |
| Yttrium | Y | 39 |
| Lanthanum | La | 57 |
| Cerium | Ce | 58 |
| Praseodymium | Pr | 59 |
| Neodymium | Nd | 60 |
| Promethium* | Pm | 61 |
| Samarium | Sm | 62 |
| Europium | Eu | 63 |
| Gadolinium | Gd | 64 |
| Terbium | Tb | 65 |
| Dysprosium | Dy | 66 |
| Holmium | Ho | 67 |
| Erbium | Er | 68 |
| Thulium | Tm | 69 |
| Ytterbium | Yb | 70 |
| Lutetium | Lu | 71 |
Of these, the most important for industrial purposes are neodymium, dysprosium, europium, terbium, and yttrium.
Promethium is a special case and uniquely different from the other rare earths as it is radioactive. It has a half-life of 17.7 years, which means that every 17.7 years half of it decays into another element, which in this case is neodymium.
Given that that decay process has been going on since the planet was formed, there is only a tiny amount of promethium remaining in the earth’s crust. However, it can be manufactured from uranium 235 in nuclear reactors.
How are rare earth minerals mined?
Rare earths occur in around 160 known minerals, but only a few of these are currently mined. These are:
- Bastnasite, a fluorocarbonate, is the main source of rare earths accounting for around 94% of the world’s rare earth minerals.
- Laterite clays occur in China and are rich in lanthanides and yttrium.
- Monazite, a phosphate, once accounted for around 40% of rare earths mines, but now its contribution is minimal.
- Loparite is also a phosphate but richer in lanthanides and yttrium.
Mining rare earth minerals is challenging. Usually they occur on the same site in many different minerals such as fluorites, carbonates, and phosphates, and any given mineral may contain multiple rare earth elements.
For example, at the Chinese Bayan Obo mine, which supplies almost half the world’s supply of rare earth elements, rare earths occur in 15 different minerals as the tailings of iron ore mining.
How are rare earth minerals refined?
Refining rare earth minerals is highly complex, difficult and expensive. The rare earth metals are chemically very similar, so separating and purifying them is challenging. The precise process depends on the kind of ore, but in general, the following method is typical.
- The first stage is to concentrate the rare earths in the ores from less than 10% concentration to 60%. To achieve this, the ore is ground to a fine powder and separated using either floatation, electrostatic or magnetic separation.
- The concentrated ore is treated with hydrochloric acid, which removes calcite, followed by roasting, and the resulting material is leached with hydrochloric acid which dissolves the tri-valent lanthanum, neodymium, samarium, europium, gadolinium, and praseodymium. The four valent cerium is left behind and is refined chemically to various purity levels.
- The next stage is to separate out the individual rare earth elements. The process is complex and involves chelation with a complexing agent such as EDTA, ion exchange, and solvent extraction.
The rare earth metals are purified using various techniques depending on the physical and chemical properties of the specific rare earth metal. Purification usually involves calciothermic and electrolytic processes to achieve purities of from 95% to 99% or purer.
Are rare earth metals recyclable?
Although there are numerous potential sources for recycling, doing so is dangerous for the environment and individuals. In practice, less than one percent of rare earths are recycled.
Where are rare earth metals produced?
As mentioned above, today most rare earth elements come from China, but that is a relatively recent phenomenon. Before 1948, most came from Brazil and India, then a rich vein was discovered in South Africa, and the country became the primary source throughout the 1950s.
Another vein was found in California, and the US became the main supplier throughout the 1960s to the 1980s. From then on production in China grew, and today the country produces around 80% of rare earths and is the sole producer of the heavier rare earth elements such as dysprosium.
How are rare earth metals used in everyday life?
if you want to learn more how rare earth metals are used, please follow the link.
