Rhenium is a new and special industrial metal. It is rare in metallurgy, difficult to extract, has a high cost of extraction and is prized by society for the properties it brings to some high-tech products. It has some similar properties to the Platinum Group Metals (PGMs) and shares other properties with refractory metals. When it is in its ‘great’ form it has a white, platinum-like appearance but is a dull grey when in its powder form.
When the Periodic Table was first introduced in 1869, rhenium was one of the unknown elements. It was predicted to exist by D.I. Mendeleeff, who thought it should have similar properties to manganese, but it wasn’t until 1925 that Ida Tacke, Walter Noddack and O. Berg of Germany claimed the first identification by obtaining 1 mg of the element in an Ural native platinum ore. They later went on to process metallic rhenium from a virtually pure sample of molybdenite, (MoS2 58% molybdenum, 39.8% sulphur and 2 ppm Re).
At room temperature, rhenium is inert in air, but when temperatures reach above 400°C it will rapidly oxidise forming a heptoxide which is soluble in both water and alcohol. It has a high volatility in the heptoxide form and the relative solubilities in water and oxygenated solvents are used in rhenium recovery. At high temperatures it corrodes with sulphuric acid. Rhenium can be attacked by hydrochloric acid, but oxidizes with nitric acid.
Rhenium has oxidation states of I-VII and valences of 1, 2, 3, 4, 5, 6 and 7, which can easily change. This makes it a highly desirable component in catalysts. Due to its high susceptibility to oxidation some degradation may take place at high temperatures. As rhenium’s properties rely heavily on its purity, experimental conditions must be carefully maintained.
Relative Atomic Mass
The driving force of the Rhenium market over the last 30 years has reflected the commercialisation of Rhenium in the aero-engine industry (where it is un-substitutable) as well as its continued mature use in platinum-rhenium reforming catalysts for the oil industry.
It is an element which may be classed as rare – the 77th least abundant element in the periodic table, nowhere mined for itself, only produced as a by-product of copper (and frequently only as a by-product Molybdenum Sulphide Concentrates separated from copper porphyry ores and sent for roasting). It has a worldwide primary supply of about 45mt (less than a quarter of the supply of palladium), which rises to about 70mt when scrap and recycling is taken into account.
Its growing pains have been reflected in price. In 1979-80 prices first peaked at about $3300 per kg Re as European and U.S. laws on cleaner air led to an expansion in demand for high octane lead-free gasolines. Meanwhile the ending of the Soviet Union saw the first flows of Rhenium from East to West, largely from Kazakhstan, forcing prices down to a low of $300 per kg Re in 1996. Just twelve years later, in August 2008, Rhenium reached a peak of $12,000 per kg as a result of the combined demand for units for both aerospace and industrial gas turbines, as well as the then (but now abandoned) prospects of Rhenium’s use in catalyst formulations for gas to liquids technology (GTL).
The biggest recent structural change to the market came about after 2008 when, thanks to the incentive provided by high prices, ways were found to extract rhenium from spent Nickel-alloy, and methods to clean spent super alloy for reverting into new melts. In this way the total supply of Re units rose by over 50% and led to a steady fall in prices over the following decade. At the time of writing (2020) with prices circa $1000 per kg Re, a number of scrap recovery works have closed, which suggests the supply base will be likely now to contract again.
Lipmann Walton & Co Ltd's main business in Rhenium consists of sourcing a wide range of Re-containing raw materials which are then converted and upgraded at Heraeus Deutschland GmbH in Germany. Both rhenium pellets and very pure catalyst grade ammonium perrhenate are then stocked for customers.
Our Re metal pellets have been approved for use as virgin addition in super alloys destined for precision casting into single crystal turbine blades by most aero-engine and gas turbine manufacturers. We are also AS 9120 certified ensuring full traceability.
So called second generation alloys contained typically Re 3%, third generation 6% and now the 4th generation, yet to be commercialised, will contain Re 6% and Ru 3%.
These same alloys are also used in industrial gas turbine capacity which remains a significant slice of today's deregulated electricity supply industry. These blades, as in aero-engines, must meet the same requirements of high operating temperatures, creep resistance and anti NOx emissions.
Geologically, Rhenium is an element precariously dependent on one region, Chile, for its supply, where the majority of porphyry (volcanic) copper ores are mined. With 65% of output originating here, the world's leading producers, namely Molymet (the world's leading producer of Molybdenum) as well as Molyb, the by product arm of the state producer Codelco, have a leading role. Both treat their by-product MoS2 locally by roasting and capturing rhenium from the sulphur flue gases thus generated, which are then treated hydrometallurgically.
Most contracts in rhenium are written as long-term multi-year agreements between producers and aero-engine makers, but an active free market also exists around the world, where spot demand for catalyst making and new alloy are filled from local markets and merchants such as ourselves who are able to supply, in spec, on time, and from stock.
Leading trade publications such as Fastmarkets (formerly London Metal Bulletin) and Argus Metals report prices for reference.