Criticality of metals and metalloids

Abstract

Imbalances between metal supply and demand, real or anticipated, have inspired the concept of metal criticality. We here characterize the criticality of 62 metals and metalloids in a 3D "criticality space" consisting of supply risk, environmental implications, and vulnerability to supply restriction. Contributing factors that lead to extreme values include high geopolitical concentration of primary production, lack of available suitable substitutes, and political instability. The results show that the limitations for many metals important in emerging electronics (e.g., gallium and selenium) are largely those related to supply risk; those of platinum group metals, gold, and mercury, to environmental implications; and steel alloying elements (e.g., chromium and niobium) as well as elements used in high-temperature alloys (e.g., tungsten and molybdenum), to vulnerability to supply restriction. The metals of most concern tend to be those available largely or entirely as byproducts, used in small quantities for highly specialized applications, and possessing no effective substitutes.

Keywords: economic geology; materials science; substitution; supply risk; sustainability.

Fig. 1.

The concentrations (parts per million) of 44 elements found on printed circuit boards (33).

Fig. 2.

The methodology of criticality at the national level. The axes in criticality space are supply risk, environmental implications, and vulnerability to supply restriction. Several indicators on each axis are aggregated to arrive at a criticality assessment, as indicated in the diagram. WGI, World Governance Institute. Data sources for the assessment are metal in-use stock determinations, metal material flow analysis, metal substitution potential, country-level information, and environmental life cycle assessment results (comparison on the basis of 1 kg of each element at the factory gate). The global methodology is similar, but omits social and regulatory and geopolitical components on the supply risk axis and the susceptibility component and net import reliance ratio and national economic importance from the vulnerability to supply restriction axis.

Fig. 3.

Evaluation of criticality indicators, components, and axes, global and US levels, 2008 epoch. The abbreviations are defined in SI Appendix, section 1.

Fig. 4.

(A) The global assessment for 62 metals, 2008 epoch, global level, in criticality space. The highest level of criticality is at 100, 100, 100 (Back Right Top). The metals assigned to the several groupings are indicated in color on the periodic table. (B) Hierarchical cluster analysis dendrogram of the results shown in A.

Fig. 5.

Two-axes criticality plots for 62 metals, 2008 epoch, global level, with hierarchical clustering of elements identified. (A) Supply risk versus vulnerability to supply restriction, (B) environmental implications versus vulnerability to supply restriction, and (C) supply risk versus environmental implications. Dendrograms for these displays are given in SI Appendix.

Fig. 6.

Periodic tables of criticality for 62 metals, 2008 epoch, global level for (A) supply risk, (B) environmental implications, and (C) vulnerability to supply restriction.