READERS may be forgiven for not having heard of rhenium (chemical symbol Re). It was discovered comparatively recently in 1925 and, at seven parts per billion, is one of the rarest elements in the Earth’s crust. Despite its elusiveness, the metal’s unique characteristics, including a high melting point of 3,186°C, endear it to manufacturers of things like jet engines. With the continuing global boom in air travel, its value has soared, increasing sevenfold since 2005, and making it one of the dearest industrial metals, and a darling of commodities speculators.
Until natural deposits start running dry, higher demand will probably be met through increased extraction, still the most economically viable solution. However, a new report just published by the United Nations Environment Programme (UNEP) warns that this approach may be unsustainable.
For a start, extraction of rhenium cannot be ramped up at will. It is a so-called companion metal, left over from molybdenum production, itself a by-product of copper mining. As such, its supply is tied to demand for copper. Second, like many metals, rhenium occurs naturally in specific pockets. The vast majority of global rhenium is produced in just two countries, Chile and Kazakhstan.
In principle, aircraft do not need rhenium to stay aloft. However, as Thomas Graedel, an industrial ecologist at Yale University, and the lead author of the UNEP report, points out, the reason many modern products work so well is that they use materials whose properties are just so. “Without them, performance would suffer – slower computers, fuzzier medical images, heavier and slower aircraft.”
One way to deal with limited supply of raw materials is to look for suitable alternatives. General Electric, one of the world’s biggest makers of jet engines, has spent years developing nickel-based superalloys to replace rhenium. But the best GE’s boffins could manage was to reduce the amount of metal required, not eliminate it altogether. Moreover, few manufacturers possess the resources to achieve even such limited progress.
The second option is to recycle. Unlike over one-third of all metals, rhenium has actually seen a rise in recycling rates (although less than a quarter of the stuff found in new jet engines is second-hand). This has been helped by its frothy price, and the fact that it is easy enough to pinpoint and extract from scrapped jet engines. By contrast,
modern mobile phones, which may contain up to sixty useful and rare metals, are too small and fiddly for triage to be worth the effort. The upshot is that many valuable materials end up in landfills or are melted into new metallic alloys, wasting their unique properties.
It would be foolish to underestimate the ability of materials scientists to come up with clever way to do without scarce metals. But research and development take time. Even if they do eventually succeed, the periodic table may have shrunk, leaving producers of fancy gadgets in the lurch. It may turn out that for a vast array of metals, recycling will soon no longer be a lifestyle choice; it shall become an economic exigency.
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Rare metals – re cycling