Freeport McMoRan’s Sierrita mine south of Tucson is the only U.S. source of Rhenium, a metal used in high-temperature super-alloy turbine blades for jet aircraft and other land-based turbines. About 6% rhenium in the jet turbine blades allow the engines to develop much more thrust. Rhenium is also used, with platinum, as a catalyst to make high-octane hydrocarbons which are used in lead-free gasoline. Other uses, mainly as alloys with tungsten or molybdenum, include electrical contact points, flashbulbs, heating elements, metallic coatings, thermocouples, and x-ray tubes.
Rhenium occurs in the mineral molybdenite (molybdenum sulfide), a by-product of some porphyry copper mines. When the molybdenite concentrate is roasted, rhenium is recovered from the stack gases. Currently, the Sierrita plant is the only one in the U.S. equipped to recover rhenium. Rhenium is sold as powdered metal and as ammonium perrhenate for about $10,000 per kilogram. In 2008 (the latest figures available from the USGS), Sierrita produced almost 8,000 kilograms.
Sierrita’s production represents about 15% of our total consumption. Our major imports of rhenium metal come from Chile, Germany, and the Netherlands. Rhenium as ammonium perrhenate is imported from Chile, China, Germany, and Kazakhstan.
Possible future sources of rhenium involve recycling turbine blades from older decommissioned jet turbine blades which contain 3% rhenium. However, the technology does not yet exist. Another possible source would be to equip more molybdenum plants with the equipment to recover rhenium.
Data source: United States Geological Survey