[LUM#14] Precious Gems

[LUM Magazine] - Published on March 30, 2021 under Research Centers, Research Units

How can we achieve the cleanest possible ecological transition? Thanks to geologists. Three researchers from the Géosciences Montpellier* laboratory aim to better understand the processes involved in the formation of rare metals used in so-called “green” technologies in order to relocate and facilitate their extraction.

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Lithium, tungsten, germanium, gallium, indium… These metals all share one thing in common: they are indispensable to new technologies. Tungsten? Valuable in certain aerospace alloys. Lithium? Essential to automotive and computer technologies. As for the rare metals—gallium, germanium, and indium—they are necessary for the manufacture of solar panels, making them indispensable components in the development of renewable energy.

“To reduce our carbon emissions, we’re embracing renewable energy, which is sometimes considered clean energy,” explains Bénédicte Cenki-Tok. “But the only clean energy is the energy we don’t use , ” the geologist adds. And for good reason: the supply chain for these so-called rare metals used in green technologies can hardly be described as “clean.”

"Clean" Energy

“Currently, the global market for rare metals is dominated by China,” explains Alexandre Cugerone, who wrote his thesis on this topic. “Europe is almost entirely dependent on Asia, the Americas, and Africa. “It is particularly paradoxical that we import metal resources for our 21st-century technologies—some of which are strongly associated with ‘green’ or ‘renewable’ initiatives—from distant countries with lax or nonexistent environmental regulations for mining,” laments the researcher.

That’s where geologists come in. “These metals are essential for developing these technologies, so what we need to do is try to mine them in a thoughtful and intelligent way, ” explains Émilien Oliot. And to mine them more effectively, it is first and foremost necessary to understand how they form and become concentrated in nature. “We’ve long understood the processes that create metamorphic rocks and mountain ranges, as well asthe temperature and pressure conditions inherent in their formation. This knowledge, which may seem outdated, is in fact precisely what allows us to understand the processes of formation and concentration of the critical metals used in modern technologies,” adds Bénédicte Cenki-Tok.

Mining spoil heaps

The geologists’ goal: to inspire new, eco-friendly methods for exploring and recovering certain types of waste from past mining operations. After all, these precious metals aren’t found only on the other side of the world—they’re sometimes right under our noses, or almost. “For certain rare metals, we know which host minerals contain them, so we know where to look for them,” explains Emilien Oliot. Where? In mine tailings piles, for example—those artificial hills formed by the accumulation of mining byproducts.

These critical metals are found either in minute quantities, scattered throughout base metals such as zinc and copper, or sometimes in highly concentrated minerals smaller than one-tenth of a millimeter. To better understand the value of these tailings piles, researchers use a culinary analogy. “Consider a single cake, with cocoa powder evenly distributed throughout the batter, and chocolate chips. In what form is the chocolate easiest for chocolate lovers to recover once the cake is baked? The chocolate chips, of course. The principle is the same in our study: it is easier to extract critical metals concentrated in small minerals—our chocolate chips—rather than those scattered throughout the base ore—the chocolate powder in the cake batter.”

Chocolate chips

For example, researchers have shown that the deformation of zinc sulfide ore—which occurs simultaneously with the formation of mountain ranges—promotes the re-concentration of germanium in hyperconcentrated minerals, “our famous chocolate nuggets, which are found in particular in the heart of the Pyrenees.” For geologists, it is therefore very interesting to search for mining sites where deformation caused by natural geological processes has acted as a “natural concentrator” of rare metals.

“Many mining sites were formerly exploited solely for their base metals, and the tailings from this past mining activity could be put to good use, particularly in the Pyrenees, the Massif Central, as well as in the Alps and the Scandinavian mountains of northern Europe. They may constitute potential sources of rare metals,” the geologists point out.

Redistribute resources

There is another significant advantage: these metals might be easier to extract. “When a rare metal, such as germanium, is scattered throughout the ore, extraction is complex and requires labor-intensive processes. However, if these rare metals are concentrated—like chocolate chips—in small minerals, separating them could be simplified, ” explains Alexandre Cugerone.

A promising path toward ending European countries’ near-total dependence on rare metals. “The social and environmental impacts of this mining are cause for concern; we cannot simply shift the pollution generated by it elsewhere,” geologists warn. “Above all, we must work inclusively with producing countries and involve all stakeholders in order to better redistribute resources. ” Let everyone have their share… of the pie.