Conserving functionality of relatively rare metals associated with steel life cycles: a review

Steel often contains relatively rare metals. These metals are geochemically relatively scarce (having an upper crustal abundance < ∼0.025 (mass)%) or subject to national stockpiling to prevent shortages in supply. Examples are: Cr, Mn, Mo, Nb, Ni, V and W. Relatively rare metals can be intentionally added to steel: they are then functional. Currently, during a small number of steel life cycles these metals lose functionality. Functional relatively rare metals can also be present in surface coatings and joining materials for steel. These may also lose functionality. This paper considers options for conserving the functionality of the relatively rare metals associated with steel life cycles. These include changes in the composition of steel and surface coatings, e.g. by substituting the relatively rare metals by more abundant ones or selecting functional metals with reduced losses to production residues. Other possibilities are using mechanical fasteners that allow for easy disassembly, replacing recycling by re-melting by solid state technologies, reducing losses of relatively rare metals to steel production residues by optimizing melting conditions and increased recycling of production residues. Further options regard extending the service life of steel products and components to minimize under-exploitation, furthering end-of life disassembly and increasing source-separation and closed-loop recycling of end-of-life steel. Recovering relatively rare metals from steel production residues, options for the improvement thereof, and incentives for conserving relatively rare functional metals are also discussed.