[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 Montpellier Geosciences Laboratory* aim to better understand the processes involved in the formation of rare metals used in so-called “green” technologies, with the goal of relocating and facilitating 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 turning to 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 points out. 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. “ Importing metal resources for our 21st-century technologies—some of which have strong ‘green’ or ‘renewable’ connotations —from distant countries with lax or nonexistent environmental regulations is particularly paradoxical,” laments the researcher.

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 This knowledge, which may seem outdated, is in fact precisely what allows us to understand the processes of formation and concentration of the critical metals involved in modern technologies,” adds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

Mining spoil heaps

The geologists’ goal: to inspire new, eco-friendly methods for exploring and recycling certain types of waste from past mining operations. Because these precious metals aren’t found only on the other side of the world, but 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 built up from the accumulation of mining byproducts.

These critical metals are found either in minute quantities, scattered throughout base ores 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 which form is the chocolate easiest for food lovers to recover once the cake is baked? The 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 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 hyper-concentrated minerals —“our famous chocolate nuggets, which are found particularly in the heart of the Pyrenees.” For geologists, it therefore becomes 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 historically 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 represent potential sources of rare metals,” the geologists point out.

Redistribute resources

With 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 heavy-duty processes. However, if these rare metals are concentrated—like chocolate chips—in small minerals, separating them could be simplified, ” explains Alexandre Cugerone.

A promising approach to breaking 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. "