Critical, Rare, and Strategic Metals in Sustainable Metallurgy: A few Definitions, Supply Risks, and Key Examples

Metals and minerals underpin countless modern technologies, from everyday consumer electronics, medical, transportation, energy to strategic manufacturing systems. As global demand for advanced devices, electric vehicles, and renewable energy infrastructure grows, so does the urgency of securing a stable supply of specific metals. Terms like “critical,” “rare,” or “strategic” are used to highlight metals whose availability is not guaranteed—or whose scarcity and supply constraints pose potential risks for industries and national security. Yet the meaning behind these labels goes beyond mere geological abundance. Economic viability, geopolitical concentration, the substitutability of these metals in key applications, and the environmental costs of extraction and refining are all important factors. By examining how metals transition from “abundant” or “common” status to “rare,” “high risk,” or “critical,” it becomes easier to see why supply chains for certain elements require special attention in sustainable metallurgy.

In discussions about whether a metal is “rare” or “abundant,” context is essential. The Earth’s crust contains nearly all chemical elements, but in vastly different concentrations. Some metals, like iron (about 5% in the Earth’s crust) and aluminum (around 8%), are so abundant and widely distributed that large, economically minable deposits are relatively common. Others, like lithium or the rare earth elements, are moderately present in Earth’s crust (on the order of tens to hundreds of parts per million), yet often only found at commercially viable grades in limited geological settings.

Quantifying whether a metal is “rare” involves distinguishing between reserves, resources, and geopotentials. A resource reflects the total amount of a metal in identified or undiscovered mineral deposits that, in principle, could be mined in the future. A reserve is the fraction of that resource which can be extracted economically and legally under current market and technological conditions. For instance, the overall resource base for copper may be over a billion metric tons in terms of geological estimates, yet the current global reserve—the portion feasible to mine profitably—is significantly lower. This gap arises because most copper ores contain anywhere from 0.3% to 2.0% copper by weight, and it is only those deposits that can be mined and processed at a margin above production costs that qualify as reserves.

Similarly, nickel has a crustal abundance of roughly 80 parts per million, but many nickel deposits (sulfide or laterite) have ore grades in the range of 0.5% to 3% Ni. Large-scale production of nickel stands at about 2.5 million metric tons per year, meeting demand for stainless steel, battery precursors, and specialty alloys. However, if demand surges—particularly from the electric vehicle sector—low-grade deposits might become economically attractive, changing their status from “resource” to “reserve.” This dynamic process depends not only on geology but also on technology (e.g., more efficient hydrometallurgical processes) and market forces (nickel prices).

A metal becomes “critical” or “strategic” when its supply risk is judged high relative to its importance for key applications. If a metal is crucial for national security or for enabling large-scale technologies with few good substitutes, any disruption or shortfall can ripple through industries. Traditional examples include platinum group metals for catalytic converters or defense electronics, tungsten for specialized alloys, and rare earth elements for permanent magnets in wind turbines and electric motors.

In deciding whether a metal is critical, analysts often consider:

1. Supply Concentration: The degree to which extraction and processing are dominated by a few countries or companies. 

2. Vulnerability to Disruption: The likelihood of geopolitically driven export restrictions, trade disputes, or natural disasters that might halt production. 

3. Lack of Substitutes: The difficulty or impossibility of replacing a metal in a given application without sacrificing performance or drastically increasing cost. 

4. Market Growth: Potential for rapid demand growth outpacing current and future supply, leading to price volatility. 

“Strategic” metals tend to be those viewed as indispensable for national defense, economic stability, or critical infrastructure. This category overlaps significantly with “critical” metals but often emphasizes security stockpiling and the risk of embargo or geopolitical pressures. Defense industries, for instance, rely on specialized alloys containing rhenium or cobalt for jet engines, making these metals strategic because disruptions could threaten military readiness.

Many metals are called “rare” not only because of their relatively low abundance but because of the challenges in discovering and exploiting concentrated deposits. Rare earth elements (REEs) such as neodymium, dysprosium, and europium each have specific crustal abundances on the order of a few parts per million. Although collectively they are more common than silver or gold, REEs rarely occur in high-grade ores, thus limiting the number of active mines. Global production of rare earth oxides is on the order of a couple hundred thousand metric tons per year, with the majority historically coming from a small number of locations. When demand for rare earth magnets in motors and generators rises, any supply disruption can lead to significant price spikes and production bottlenecks.

Lithium is another example. While its crustal abundance is around 20 parts per million, economic extraction typically occurs from either hard rock (spodumene) ore, which can range from 1% to 2% Li by weight, or lithium brine deposits containing around 200 to 3,000 milligrams of lithium per liter. Annual lithium output in recent years has exceeded 100,000 metric tons, and forecasts suggest demand could grow by more than fivefold within the next decade due to lithium-ion batteries for electric vehicles. Such rapid expansion leads to concerns about supply bottlenecks and environmental impacts, since lithium brine extraction in arid regions can compete with local water usage and ecosystems.

Cobalt and nickel highlight the “high risk” aspect as well. Cobalt mining exceeds 160,000 metric tons per year, with over half sourced from the Democratic Republic of Congo. Political instability, artisanal mining with minimal oversight, and fluctuating global prices create an environment in which short-term disruptions or long-term underinvestment can severely affect production volumes. Nickel, though more widely distributed, still faces hurdles in developing lower-grade deposits or dealing with large volumes of overburden material. Extracting either metal often results in significant energy requirements and a substantial carbon footprint, contributing to broader sustainability concerns.

Supply risk can be approximated by metrics that combine geological data, production statistics, and political stability indices. For instance, a measure of “country concentration” might reveal how dependent the global market is on just one or two nations. Price volatility can be another quantitative indicator, where metals like cobalt or rare earths can experience price swings of over 100% in a single year, reflecting tight supply and speculative trading. In contrast, abundant metals like iron or aluminum often exhibit less extreme volatility, thanks to broader geographical distribution and well-established infrastructures.

Environmental metrics come into play when evaluating critical metals. Low ore grades demand large-scale material movement and energy inputs, raising greenhouse gas emissions, water consumption, and waste generation per unit of metal. Nickel laterite ores, for example, can require over 3 to 5 times more energy to process compared to nickel sulfides. Cobalt extraction from copper-cobalt ores commonly produces tailings that contain residual heavy metals, creating long-term disposal challenges. When scaling up production to meet a booming electric vehicle market, these environmental costs become even more pronounced.

Concerns around critical, rare, and high-risk metals motivate several strategies aimed at reducing supply vulnerabilities and environmental impacts:

1. Diversification of Supply: Developing new mines and refineries in stable regions to mitigate geographical concentration. 

2. Technological Innovation: Improving ore processing, expanding low-grade deposit viability, and reducing energy and chemical demands. 

3. Substitution and Materials Engineering: Designing components that either use less of a critical metal or can switch to more readily available elements without substantial performance loss. 

4. Recycling and Circular Economy: Capturing end-of-life products containing metals like lithium, cobalt, or rare earths, then refining them back into high-purity materials. Although still a relatively small fraction of global supply, this “urban mining” model can greatly reduce primary extraction. 

5. Strategic Stockpiling: Governments or industries may maintain inventories of essential metals to buffer against short-term supply disruptions and price spikes.

Demand for metals used in clean energy and high-tech devices is forecast to grow sharply over the coming decades, making these strategies increasingly urgent. Rising electric vehicle production alone could account for more than half of lithium and cobalt consumption within a decade, and copper demand for electrification might outstrip existing mining capacity if new projects fail to keep pace. As a result, evaluating metals as “critical,” “rare,” or “strategic” rests on an ever-shifting balance of economic, political, and technological factors. Sustainable metallurgy aims to address these complexities, ensuring that future resource needs can be met without causing excessive social or ecological harm. By deepening our quantitative understanding of deposits, refining technologies for ore processing and recycling, and pursuing balanced resource policies, societies can better manage the complexities surrounding metals that are increasingly recognized as essential yet perilously at risk.