By-product metals are technologically essential but have problematic supply

Abstract

The growth in technological innovation that has occurred over the past decades has, in part, been possible because an increasing number of metals of the periodic table are used to perform specialized functions. However, there have been increasing concerns regarding the reliability of supply of some of these metals. A main contributor to these concerns is the fact that many of these metals are recovered only as by-products from a limited number of geopolitically concentrated ore deposits, rendering their supplies unable to respond to rapid changes in demand. Companionality is the degree to which a metal is obtained largely or entirely as a by-product of one or more host metals from geologic ores. The dependence of companion metal availability on the production of the host metals introduces a new facet of supply risk to modern technology. We evaluated companionality for 62 different metals and metalloids, and show that 61% (38 of 62) have companionality greater than 50%. Eighteen of the 38-including such technologically essential elements as germanium, terbium, and dysprosium-are further characterized as having geopolitically concentrated production and extremely low rates of end-of-life recycling. It is this subset of companion metals-vital in current technologies such as electronics, solar energy, medical imaging, energy-efficient lighting, and other state-of-the-art products-that may be at the greatest risk of supply constraints in the coming decades.

Keywords: critical metals; industrial ecology; mineral production; resource management; sustainability.

Fig. 1. The periodic table of companionality on a global basis for 2008.

Metals that are mainly produced as hosts appear in blue, and those that are mainly produced as companions are in red. Details regarding data sources and assumptions are presented in the Supplementary Materials.

Fig. 2. The wheel of metal companionality.

The principal host metals form the inner circle. Companion elements appear in the outer circle at distances proportional to the percentage of their primary production (from 100 to 0%) that originates with the host metal indicated. The companion elements in the white region of the outer circle are elements for which the percentage of their production that originates with the host metal indicated has not been determined. Data sources and assumptions for the assessment are given in the Supplementary Materials. Inspired by a diagram developed by (10).

Fig. 3. Companionality dynamics.

(A to H) Variations in host metal contributions (vertical axis) for cobalt (A), nickel (B), copper (C), molybdenum (D), silver (E), platinum (F), rhenium (G), and gold (H) as a percentage of total primary production over several years (horizontal axis). Data are from (, –39).

Fig. 4. Companionality, primary production concentration, and end-of-life recycling for 62 metals.

Primary production concentration is measured by the HHI, which is calculated as the sum of the squares of the individual country production shares. Where data for multiple production stages (for example, mining, smelting, and refining) are reported, the production stage that yields the largest HHI value is used. Top and side inserts indicate distributions along respective axis. Data sources and assumptions for the assessment of companionality and production concentration are given in the Supplementary Materials (tables S1 and S2). End-of-life recycling rate ranges are obtained from (24).

Fig. 5. Revenue contribution by metal (in descending order) for five mines producing platinum group elements.

The red line marks the point at which revenues cover the cost of sales, thus defining dependency of the metals. For the Canadian and U.S. mines, costs of sales exceed revenues, as indicated by the red number at the right. Details regarding data sources (that is, company annual reports) and assumptions are noted in the Supplementary Materials.

Fig. 6. Economic companionality assessment.

(A to E) 2008 companionality of platinum (A), palladium (B), rhodium (C), ruthenium (D), and iridium (E) calculated on the basis of each metal’s revenue contribution relative to the cost of sales on an operation-by-operation basis for 36 operations (column height) displayed in ascending order. Column widths are proportional to each operation’s sales contribution as percent of global sales. Sales-weighted averages for each metal are represented by horizontal lines.