Metals in short supply: a challenge for tomorrow's societies

Many metals are essential for 21st century technologies, and in particular for many "green" technologies, such as batteries, solar panels,wind turbine magnets and fiber optics. Some of these metals are "critical" because their supply is uncertain.

Alexandre Cugerone, University of MontpellierBénédicte Cenki-Tok, University of Montpellier and Emilien OLIOT, University of Montpellier

Zinc ore can contain important resources of critical metals useful for new technologies. Here, microscopy of ore from Arre-Anglas (Pyrenees). Alexandre Cugerone, Author provided

Our aim is to understand how certain critical metals are concentrated in the earth's crust so that they can be extracted more easily, and to inspire new methods of exploration and eco-responsible recovery of certain waste products from past mining operations, particularly in France and Europe.

In fact, these critical metals(rare earths, cobalt, lithium, platinoids, germanium, etc.) are found either in minute quantities, disseminated in base ores such as zinc and copper, or, sometimes, in hyper-concentrated minerals, smaller than a tenth of a millimeter. To understand this fundamental difference with an everyday example, let's consider a single chocolate cake, with melted chocolate evenly distributed throughout the cake batter, and chocolate chips. In which form is the chocolate easiest for gourmands to retrieve once the cake has been made? Chips, of course! The principle is the same in our study: it's easier to extract critical metals in small, concentrated minerals (our chocolate chips) rather than scattered in the base mineral (the melted chocolate in the cake mass).

The difficult supply of tomorrow's metals

Many natural metallic substances are still mined today, such as base and ferrous metals (copper, zinc, iron, manganese, etc.) or precious metals (gold, silver, platinum, etc.). Technological metals", such as lithium, rare earths, tungsten or other rare metals (germanium, gallium, indium), have been made indispensable by the digital revolution, and are also crucial to the development of "green technologies".




See also:
Why do we talk about the "criticality" of materials?


If we continue to extract these technological metals, at the current rate and under these conditions, when most are considered critical, we could face a supply crisis and significant environmental effects.

Current and future uses of rare metals associated with zinc deposits.
Author provided

Among these critical metals, elements from the "rare earth" group, as well as lithium and cobalt, are essential to new automotive and computer technologies. Tungsten is invaluable in certain aerospace alloys. Rare metals such as gallium, germanium and indium are essential to the manufacture of fiber optics, solar panels and electronic systems, and could improve the performance of lithium-ion batteries. The latter are extracted mainly as a by-product of zinc sulfide, in which they are diluted.

Where are rare metals concentrated and how can they be better extracted?

Our study shows that rare metals such as germanium, gallium and indium can exist in minute quantities, disseminated in base metal crystals, but also in small, hyperconcentrated carrier minerals. We have demonstrated that the deformation of zinc sulfide ore, contemporaneous with the formation of mountain ranges, favors the re-concentration of germanium in hyper-concentrated minerals (our chocolate chips) at the heart of mountain ranges, in this case the Pyrenees.

As a result, it becomes very interesting to look for mining sites where deformation by natural geological processes has acted as a "natural concentrator" of rare metals.

A naturally deformed germanium-rich zinc sulfide (ZnS) vein in an old mine at Arre in the Pyrénées Atlantiques region. A. Outcrop of a zinc sulfide vein (modified from Cugerone et al., 2019). B. Natural deformation in zinc sulfide under the microscope, materialized by the presence of numerous schistosity planes. C. Germanium minerals associated with zinc sulfide.
Author provided

This may apply to the rare metals listed, but could also appear for other technological metals, such as the rare earth elements. Many mining sites were once exploited for their base metals (only) and, at present, many tailings or mine dumps from this past exploitation could be valorized. There may be significant concentrations of rare metals in these mining spoil heaps, particularly in the Pyrenees, the Massif Central, but also in the Alps, or in the Scandinavian mountains of northern Europe, and may constitute potential rare metal resources.

Moreover, when a rare metal, such as germanium, is disseminated in the ore,extraction is complex, requires heavy hydrometallurgical processes and induces high losses during extraction. On the other hand, if these rare metals are concentrated (like chocolate chips in a cake) in small minerals, their separation by various mechanical processes could be improved and better exploited, whether in current mining sites or in certain slag heaps or mining waste.

Our study suggests rapid, low-cost techniques for characterizing the mineralogical texture (crystal size and shape) and chemistry of rock samples, locating rare metals and assessing their concentration and potential extraction.

A way out of Europe's almost total dependence on metal resources?

Today, the world market for rare metals (gallium, germanium, indium) and rare earths is dominated by China. Europe is almost totally dependent on Asia, the Americas and Africa. But what would be the economic consequences for our industries if a supply crisis in mineral resources, particularly in "technological metals", were to arise between our countries or continents?

Map of countries representing the largest share of the world market for each metal designated as "critical" by the European Union. Rare metals are framed in red (situation in 2017).
European Commission

Social and environmental impacts

The import of metal resources for our 21st century technologies, some with a strong "green" or "renewable" connotation, from faraway countries with lax or non-existent environmental rules on mining, is particularly paradoxical.




Also read:
Rare earths: our ultra-dependence on China (and how to get out of it)


Wouldn't one solution be to extract our metals, for example from some of Europe's critical metal-rich mine dumps, in eco-responsible and environmentally-friendly ways? We need a better understanding of how critical minerals form and concentrate in chemical and geological terms, which could enable us to revisit some old mines and valorize their mining dumps.The Conversation

Alexandre Cugerone, PhD in Geosciences - Mining Geology/Metallogeny - Geosciences Montpellier, University of MontpellierBénédicte Cenki-Tok, Associate professor at Montpellier University, EU H2020 MSCA visiting researcher at Sydney University, University of Montpellier and Emilien OLIOT, Senior Lecturer in Earth Sciences, University of Montpellier

This article is republished from The Conversation under a Creative Commons license. Read theoriginal article.