Over the past years, rare earth elements have occupied an increasingly important role in modern technologies, as they are used as a basic raw material in the manufacture of many things, from smart phones to drives, wind turbines, satellites, superconductors, components of electric cars, and other modern industries.

And recently, an international team of scientists helped unravel a long-standing mystery about how underground rare earth deposits form, which sometimes appear to fade or disappear without a trace.

The results of their study on the transport of rare earth elements in and around carbonate rocks controlled by sodium, potassium and silica were published in the journal Science Advances on October 9th.

Rare earth elements

Rare Earth Elements (REEs), as defined by the International Union of Pure and Applied Chemistry, are: Rare earth minerals form a group of 17 very important chemical elements of the periodic table elements, specifically scandium, yttrium, and lanthanides.

These elements were described as "rare" due to the few places they were previously extracted from. However, recently a relatively high concentration of these elements - with the exception of unstable promethium - has been found in the earth's crust, with cerium being the element of the order of 25 of the more elements. Abundance in the earth's crust, at a concentration of 68 parts per million.

A thin strip of carbonatite rich in apatite may contain economic concentrations of rare earth elements (Kalerna - Wikipedia)

Although their name suggests they are scarce, they can in fact be relatively abundant resources in the Earth's crust, but their dispersed dispersion makes them difficult to isolate and extract from below the surface, not to mention the environmentally unfriendly extraction methods.

However, concentrated rare earths deposits are a highly desirable natural resource, and scientists are constantly looking to innovate new and better ways to find and secure precious metals.

Exploring chemical mechanisms

In the new study, a team of researchers led by geologist Michael Annenberg of the Australian National University wanted to explore the chemical mechanisms by which rare earth elements form below the surface, specifically in igneous carbonate rocks that are closely related to rare earth elements.

The researchers showed in their new study that "these rare rocks and their modified and damaged derivatives provide most of the rare earth elements in the world."

They added in their paper that "there is no standard model explaining all the features of rare earth elements deposits associated with carbonate, which severely impairs the exploration required to secure future supply."

The researchers put small amounts of synthetic carbonate into silver or nickel capsules into a piston cylinder device (Depth of the Earth - Wikipedia)

Annenberg and his team simulated what happens when carbonate rocks are heated under high pressure, before cooling and decompression, as they do in natural magma processes.

The researchers put small amounts of synthetic carbonate into silver or nickel capsules in a piston cylinder device, and subjected the samples to temperatures of up to 1,200 degrees Celsius at pressures of up to 2.5 GPa, before gradually decompressing and cooling them to 200 degrees Celsius and 0.2 GPa. Pascal.

Annenborg explained on his Twitter account that the goal of this work is to understand what is focused on rare earth elements from high-quality local deposits, and said, "So we decided to put carbonatite in a capsule and test it ourselves."

A step forward

Before the last study, it was thought that some molecules capable of binding with rare-earth elements - including chlorine and fluorine - were necessary to make them soluble and able to group them into extractable crystalline concentrations.

But that is not what the latest study showed.

Instead, the results indicate that alkaline chemicals are required to transport the rare earth elements in and around the carbonate, as the experiment showed that sodium and potassium helped make the rare earth elements soluble.

According to the researchers, the alkaline-bearing carbonatite is able to form fluids rich in rare earth elements that can migrate long distances in rock-like conditions, while maintaining a high solubility in rare earth elements.

Solid carbonate lava at Ull Duinyo Lengai volcano, Tanzania (Thomas Kraft - Wikipedia)

Neat solution

Of course, just because we've seen this in lab conditions doesn't necessarily mean we'll notice the same exact interactions in open systems in nature, where the presence of water and other chemicals in the environment can change things.

Nevertheless, it is a step forward that fixes our knowledge of the basic processes involved in the formation of rare earths, as the paper's senior author and geologist Francis Wall of the University of Exeter in the United Kingdom explains to the research news page on the university's website.

"This is an elegant solution that helps us better understand where heavy rare earths, such as dysprosium, and light rare earths such as neodymium, may be concentrated in and around carbonate intrusions," Wall says.

"We were always looking for evidence for solutions containing chloride, but we failed to find them ... These results give us new ideas."