According to the U.S. Department of the Interior, iridium in the Earth’s crust is thought to have come from the same asteroid or comet believed to have caused the extinction of dinosaurs. While crustal abundance of iridium is estimated at 0.001ppm[1], the concentrations are much higher in asteroids. Normally, iridium rains down on Earth in meteorite dust at a fairly constant rate[2]. Iridium in the clay layer that created the boundary between the cretaceous and tertiary periods (KT boundary) was 30 times greater than the amount expected. This information was what allowed scientists to develop the hypothesis that an asteroid impact caused the extinction of dinosaurs 65 million years ago (See Alvarez hypothesis).
Iridium is one of the rarest elements on Earth, but can be found in one of the most ubiquitous aspects of modern life – the car. Due to its high melting point and low reactivity, iridium is used as the contact in spark plugs. Another valuable physical property is iridium’s ability to resist corrosion, which is why the element is used to grow crystals for LED lights[3]. Interestingly, iridium was also used to create the standard meter bar used to measure the unit of distance from 1889 to 1960. The metal has several important uses in industrial chemistry, as industrial catalysts and in chlorine production.
Despite its rarity, consumption of iridium continues to increase. This is related to the demand for more energy-efficient electrical devices, in which iridium crucibles play a large role. In 2014, global iridium consumption only rose 5 percent from the previous year, however electrical applications rose by 17 percent, bringing global consumption of iridium in electrical devices to 30 percent. Demand, plus a drop in price per troy ounce, has allowed the iridium market to increase[4]. The U.S. Geological Survey expects this upward trend to continue in the electronics industry.
The problem with iridium is two-fold. First, mining and processing iridium is expensive, time-consuming, and results in significant environmental impacts. Although copper and zinc processing requires relatively low levels of energy, the additional steps to extract and refine iridium make it highly energy-intensive with large global warming potential[5] (Figures 1 and 2). Secondly, the majority of iridium is mined in South Africa, which is fraught with tension. Along with the socioeconomic, safety and environmental problems that plague mines and nearby towns, the past 10 years have seen more worker violence and strikes than any other time post-apartheid[6].
Most concerning, however, is the lack of awareness about “critical elements” like iridium. The world is likely to face shortages for many of these elements anywhere between the next five to100 years in most cases[7]. Despite this, demand for these elements is rising and will continue to do so as new applications are found. For example, in the realm of chemistry, iridium has seen increased interest for its applicability in a wide range of catalytic reactions, especially in the pharmaceutical sector, but also in biomass conversion and many other applications. As much as possible, chemistry research should be tailored to finding sustainable alternatives not only for iridium, but for all of the critical elements. The ramifications of ignoring this problem will not just affect our children and their children, but will impact our lives as well. We are poised in the unique position to take action and make lasting changes to improve our lives and the lives of future generations.
(Click Figure 2 Image to Enlarge)
[1] https://www.britannica.com/science/iridium
[2] http://undsci.berkeley.edu/lessons/pdfs/alvarez_ms.pdf
[3] https://www.bloomberg.com/news/articles/2014-02-19/iridium-climbs-to-3-month-high-amid-buying-after-...
[4] https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2014-plati.pdf
[5] http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0101298
[6] http://www.counterpunch.org/2016/08/16/south-africas-marikana-massacre-prompting-the-longest-strike-...
[7] https://www.acs.org/content/acs/en/greenchemistry/research-innovation/research-topics/endangered-ele...
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