Rhenium: The Rare Metal Inside Jet Engines

The Continental Pit at Butte, Montana, a porphyry copper–molybdenum deposit. Rhenium is recovered from the molybdenite concentrates it produces. Photograph by David John, USGS.

What rhenium is

Rhenium is a silvery-white metal with an extremely high melting point — 3,180°C — and a crystal structure stable in heat, which makes it exceptionally resistant to heat and wear.

• It is one of the rarest elements: less than one part per billion of the continental crust on average.
• It was the last stable, naturally occurring element discovered. Dmitri Mendeleev predicted it in 1871, noting two empty slots below manganese in the periodic table; German chemists Walter Noddack, Ida Tacke and Otto Berg finally isolated it in 1925, from platinum ore.
• It is named for the Rhine (Latin Rhenus).
• Since the late 1980s it has been critical to superalloys for turbine blades and to catalysts for lead-free gasoline.

What it is used for

Rhenium has 28 isotopes. Two short-lived radioactive ones, rhenium-186 and rhenium-188 (half-lives of about 90 and 17 hours), are used to treat liver and bone cancer and arthritis.

Where it comes from

Nearly all newly mined rhenium is a byproduct of copper mining.

• Porphyry copper deposits supply about 80%. The rhenium sits mostly in molybdenite, which commonly holds 100 to 3,000 parts per million of it.
• The ore itself usually holds under 0.5 grams per metric ton — recovery pays only because of the enormous tonnages mined (hundreds of millions to billions of tons), enough molybdenite to make it worthwhile, and special recovery plants.
• Most of the rest comes from sediment-hosted copper deposits in Kazakhstan (sandstone type) and Poland (the Kupferschiefer, or "copper schist"). Just where the rhenium sits in these is poorly understood — possibly in dzhezkazganite in Kazakhstan and in castaingite, a copper-rich molybdenite, in Poland.
• Small amounts come from processing roll-front sandstone uranium ores, in Kazakhstan and elsewhere.

Molybdenite, found in veins and scattered through most porphyry copper deposits, is the main source of rhenium. Photograph by David John, USGS.

How it is recovered

When molybdenite concentrates (or copper sulfide ores) are roasted, the rhenium oxidizes and rises up the flue stack with sulfur gases. Scrubbing the dust and gases yields sulfuric acid and other fluids carrying dissolved rhenium, from which it is precipitated as ammonium perrhenate (NH₄ReO₄) — a white powder, the main form in which rhenium is sold.

Supply and demand

Production, 2012:

• World mine output: 52,600 kg, about 27,000 kg of it from porphyry copper mines in Chile.
• Other producers: Peru, the United States, Kazakhstan, Uzbekistan, Russia and Armenia.
• U.S. production: 7,900 kg.

Resources:

• U.S. resources are in Arizona and Utah, with smaller ones in Montana, New Mexico and Nevada, and a large inferred resource in an unmined Alaska deposit.
• Identified resources: about 5 million kg in the United States and about 6 million kg in the rest of the world, led by Chile, Peru, Canada, Poland and Kazakhstan.

Consumption:

• World use: 50,000–55,000 kg a year in 2012, expected to reach about 71,500 kg by 2015.
• The United States is the largest consumer — 48,000 kg in 2012 — and imports nearly 80%, mostly from Chile and Kazakhstan.

Recycling: turbine blades last about 10 years, so second-generation blades (3% rhenium) are piling up. Once they can be recycled into third-generation blades, primary rhenium needs could fall by about 50%. Companies recycling molybdenum–rhenium and tungsten–rhenium scrap are multiplying, especially in the United States and Germany, and spent catalysts are recycled too.

Securing future supply

The United States is unlikely to meet its needs at home. It has substantial proven reserves in porphyry copper deposits, but extracting rhenium takes special plants: only one U.S. molybdenum roasting facility can recover it. A second, under construction, could raise U.S. output by about 50% — still far below U.S. use. Imports will likely keep supplying most of it.

The USGS studies how and where rhenium concentrates in the crust to assess where undiscovered resources may lie, and tracks world supply, demand and trade to inform national policymakers.

More: USGS rhenium statistics · porphyry copper deposit models

Sources

Based on David John, "Rhenium: a rare metal critical in modern transportation," U.S. Geological Survey Fact Sheet 2014–3101 (2015), USGS Mineral Resources Program, drawing on D.E. Polyak, "Rhenium," USGS Minerals Yearbook 2012; a work of the United States government in the public domain. The two photographs are taken from the fact sheet's PDF; its photographs of a jet engine and a rhenium crystal, from Wikimedia Commons under their photographers' licences, are not reproduced. The source spells the discoverer's name "Walker Noddack" and lists the two medical isotopes in the reverse order of their half-lives; rhenium-186 is the longer-lived.