Rhenium is considered to be a critical and strategic commodity because of the metal’s applications in defense, energy, high-tech industrial, and medical sectors. In the U.S., consumption of catalyst-grade rhenium by the petroleum industry is expected to remain high and demand for rhenium in the aerospace industry is expected to continue to increase.
Currently, the United States is a net importer of rhenium, unable to meet its rhenium requirements with domestic resources. In 2018, U.S. rhenium imports increased 22% over 2017. There are substantial, proven rhenium reserves in porphyry copper deposits in the United States, but special facilities are required to extract rhenium from the molybdenite concentrates recovered from these deposits.
Although rhenium is very rare, as far as the Critical Mineral Resources go, the economic and geopolitical-risks tied to this commodity are relatively low – aerospace companies are testing superalloys that contain one-half the rhenium currently used in engine blades, rhenium recycling processes continue to advance, and the number of companies designed to process the scap of molybdenum-rhenium and tungsten-rhenium continue to grow, especially in the United States and Germany. Accordingly, rhenium metal and catalytic-grade prices declined in 2018 for the seventh year in a row.
Beyond the basics above, what else should we know about rhenium? Check out the 15 interesting facts below!
- In 1871, the existence of rhenium was predicted by Russian chemist Dmitri Mendeleev. He noted two vacant slots below manganese on the periodic table of elements, which he had created in 1869, and predicted that these two elements would have similar properties to manganese. As a result, he called these ‘eka-manganese’, now ‘technetium’, and ‘dvi-manganese’, now ‘rhenium’. (Sanskrit: ‘eka’ means first and ‘dvi’ means second).
- In 1913, the existence of rhenium was suggested once again. English physicist Henry Moseley arranged elements in the periodic table by atomic number, not atomic weight as had been done previously, which lead to gaps in the periodic table belonging to undiscovered elements. One of these was element 75, rhenium.
- In 1925, rhenium was isolated from platinum ores by German chemists Walker Noddack, Ida Tacke, and Otto Berg. They named it after the Rhine River, located in Germany – ‘Rhenium’ comes from the Latin word ‘Rhenus’ meaning ‘Rhine’.
- In the 1950s, demand for rhenium saw a catalyst when tungsten-rhenium and molybdenum-rhenium alloys were invented and found important industrial applications.
- In the early 1970s, Chevron developed a series of platinum-rhenium catalysts that did not react with sulfur.
- Since the late 1980s, rhenium has been critical for superalloys used in turbine blades and in catalysts used to produce lead-free gasoline.
- From 2014 to 2017, U.S. rhenium import sources for ammonium perrhenate were: Kazakhstan, 34%; Canada, 19%; Republic of Korea, 13%; Germany, 10%; and other, 24%. During that same timeframe, U.S. import sources of rhenium metal powder were: Chile, 85%; Germany, 6%; Belgium, 4%; Poland, 3%; and other, 2%.
- In May 2018, the U.S. Department of the Interior, in coordination with other executive branch agencies, published a list of 35 critical minerals (83 FR 23295), including rhenium. This list was developed to serve as an initial focus, pursuant to Executive Order 13817, ‘‘A Federal Strategy to Ensure Secure and Reliable Supplies of Critical Minerals” (82 FR 60835).
- Rhenium was the last stable, naturally occurring element discovered and is one of the five major refractory metals (metals with very high resistance to heat and wear). The other refractory metals are tungsten, molybdenum, tantalum and niobium.
- Rhenium is a silvery-white, metallic element with an extremely high melting point of 3,180 degrees Celsius, the third highest melting point of all the elements (only carbon [3,500 degrees Celsius] and tungsten [3,422 degrees Celsius] have higher melting points.
- Rhenium has a density of 21.02 grams per cubic centimeter, making it the fourth densest element (only iridium, osmium, and platinum have higher densities).
- One of the rarest elements, rhenium has an average abundance of less than one part per billion in the Earth’s crust. Furthermore, rhenium has an abundance by weight in our solar system of 100 parts per trillion.
- Rhenium has the widest range of valences of any element – nine in total, ranging from –1 to +7. Rhenium forms three stable oxides: rhenium heptoxide (Re2 O7), rhenium trioxide (ReO3), and rhenium dioxide (ReO2 ) . Rhenium heptoxide is the most common.
- Most extracted rhenium is a byproduct of copper mining, with about 80 percent recovered from flue dust during the processing of molybdenite concentrates from porphyry copper deposits. Porphyry copper ores typically contain less than 0.5 grams per metric ton rhenium.
- This primary use for rhenium is in high-temperature superalloys critical in the manufacture of jet engine components. These alloys contain from 3 to 6 percent rhenium – the high-temperature properties of rhenium allow for turbine engines with prolonged life, increased performance, and enhanced operating efficiency. Rhenium alloys are also used in crucibles, electrical contacts, electromagnets, electron tubes and targets, heating elements, ionization gauges, mass spectrographs, metallic coatings, semiconductors, temperature controls, thermocouples, vacuum tubes, and flashbulbs. Rhenium catalysts are useful in the hydrogenation of fine chemicals. The petroleum industry uses platinum-rhenium catalysts to produce high-octane, lead-free gasoline – these catalysts boost the octane level of refined gasoline and improve refinery efficiency.
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