| The platinum-group elements (PGEs) are among the rarest elements in Earth's upper continental crust, yet each plays an important role in modern society. Despite their technological importance, little has been published on how much is lost during their extraction, processing, use, and recycling. Moreover, no global anthropogenic cycles or definitive estimates of global in-use stocks have been developed. Utilizing the principles of material flow analysis, this work provides estimates of global stocks and flows, losses, and recoveries of Pt, Pd, Rh, Ru and Ir at each life cycle stage. The use of Os is very small and not reported, so no analysis of this element has been performed.;Results indicate that PGE losses are greatest at the first and last life cycle stages, namely at concentration and at the end-of-life. On a relative basis, losses as a percentage of primary production across the PGEs range from approximately 23-38% on the supply-side and from 33-45% on the manufacturing, use, and disposal-side. There are, however, notable differences across both the life cycle stages and the PGEs. End-of-life losses of Pd are notably higher than those of Pt, owing to its greater use in electronics for which little end-of-life recycling occurs. In contrast, the greater use of Pt is in closed-loop industrial applications, jewelry, and investment in which minimal losses occur.;Results from the analysis of PGE stocks suggest that over half of the total quantity of PGEs that has ever been extracted is still in-use, with the remainder having been lost at the various life cycle stages. Cumulative losses of PGEs to mine tailings and at the end-of-life account for the largest share of these losses. Both categories have the potential to be a source of future PGE supply, but there are many factors that may limit that potential. Overall, geological resources are approximately an order of magnitude greater than the total quantity of PGEs that has ever been extracted. The in-use stocks are, however, growing rapidly and have already become an important source of secondary supply.;Two of the more important factors associated with material supply restrictions and with the opportunity to decrease the impact of such a restriction should it occur are examined in detail. The first evaluates the host-companion relationship of 62 metals, with special emphasis on the PGEs, to quantify the supply dependency of metals that are produced mainly as companions (i.e., byproducts). The results indicate that 38 of the 62 metals, including all of the PGEs save Pt, are produced only or mainly as byproducts (i.e., companions). Eighteen of the 38 are further characterized as having geopolitically concentrated production and by having extremely low rates of end-of-life recycling. It is this subset of metals that may be at the greatest risk of supply constraints in the coming decades.;The second factor provides an exploration of potential PGE substitutes, with a goal of highlighting aspects that may constrain substitution in each of the major commercial applications for all six PGEs. This examination reveals that substitution is often not possible, or is impractical due to various technical and economic reasons. When suitable substitutes are available they are often other PGMs or elements in close proximity to the PGMs on the periodic table, namely Ni, Co, and Au. In several cases, however, substitution has already occurred and further substitution may be limited. Furthermore, the co-production of PGMs and their most promising potential substitutes from the same mineral deposits limits their ability to substitute for one another in the event of a supply disruption. The combination of these factors suggests that PGE substitution potential for current high-volume applications is limited, and that further efforts are needed to develop new technologies that avoid the use, reduce the losses, and enhance the recovery of PGEs at each life cycle stage in order to significantly decrease our reliance on them in the future. |
