Criticality of Seven Specialty Metals

Evaluating metal criticality is a topic that addresses future metals supply and that has inspired research in corporations, academic institutions, and governments. In this article, we apply a comprehensive criticality methodology to seven specialty metalsscandium (Sc), strontium (Sr), antimony (Sb), barium (Ba), mercury (Hg), thallium (Tl), and bismuth (Bi)at the national and global levels for 2008. The results are presented along with uncertainty estimates in a three-dimensional criticality space comprised of supply risk (SR), vulnerability to supply restriction (VSR), and environmental implications (EI) axes. The SR score is the highest for antimony over the medium term (i.e., 5 to 10 years), followed very closely by bismuth and thallium; for the long term (i.e., a few decades), the highest SR is for thallium, followed very closely by antimony. Strontium and barium, followed very closely by mercury, have the lowest SR over the medium term, and mercury has the lowest SR over the long term. Mercury has the highest EI score. For VSR, thallium is the most vulnerable at both the national level (for the United States) and global level, followed by strontium at both levels. In general, specialty metals are found to possess a unique mix of sparse data, toxicity concerns (in some cases), and inadequate or nonexistent substitutes for a number of specialized uses, a situation that would seem to demand increased effort in acquiring the information needed to characterize specialty metal criticality with more rigor and transparency than is currently possible.