Rhenium and Rhenium Compounds

Abstract

Abstract Rhenium remains one of the least abundant elements, existing in nature only in trace amounts. The major commercial source of rhenium is still molybdenite as a by‐ or coproduct of porphyry copper ores but also in the sediment‐hosted copper ores of Dzhezkazgan where the mineral was designated Dzhezkazganite after the name of the area. In the past three years, production has begun from similar copper deposits in Poland. Rhenium oxides are released during the roasting of the molybdenite or processing of the copper ores and captured by wet scrubbing followed by chemical processing of the scrub liquors to recover the rhenium as ammonium perrhenate, which then can be reduced to pure metal or converted to other rhenium chemicals. The metal has many high temperature uses as a pure metal or as an alloy with the elements of molybdenum, tungsten, and nickel. Those uses include filaments in bulbs and mass spectrometers, in thermocouples, and in heating elements. Ammonium perrhenate and perrhenic acid are both used to produce petroleum and petrochemical catalysts. The greatest use today is in the production of rhenium bearing nickel‐based alloys for the production of aircraft and land‐based gas turbine blades to improve the heat resistance of those blades. The use has grown to the point of creating a deficit in availability. Consumption has exceeded production, causing an increase in price from the $1100/kg range a few years ago to as much as $1l,000/kg in early 2009. However, recovery from super alloy scrap and other recycling, as well as gas turbine engine makers reducing the level of rhenium in certain areas of the engines and eliminating it in others, has caused the price to fall back to the $6500/kg range. Rhenium forms a wide variety of compounds in oxidation states from −1 to +7. High oxidation state compounds are the most common, whereas the lower oxidation states are primarily metal carbonyls and derivatives. Polynuclear compounds that have strong metal‐metal bonds are plentiful. Very little is know about the toxicity of rhenium or its compounds primarily because they are available and are used in significantly smaller quantities than most other materials of commerce. There seems to be significant information available on the Internet concerning the experimental use of a radioactive isotope of rhenium, Re 186 HEDP (1,1 hydroxyethylidene diphosphate) to aid in the reduction of bone pain resulting from metastatic cancer.