History

(L. Rhenus: Rhine) Discovery of rhenium is generally attributed to Noddack, Tacke, and Berg, who announced in 1925 they had detected the element in platinum ore and columbite. They also found the element in gadolinite and molybdenite. By working up 660 kg of molybdenite in 1928 they were able to extract 1 g of rhenium.

Sources

Rhenium does not occur free in nature or as a compound in a distinct mineral species. It is, however, widely spread throughout the earth's crust to the extent of about 0.001 ppm. Commercial rhenium in the U.S. today is obtained from molybdenum roaster-flue dusts obtained from copper-sulfide ores mined in the vicinity of Miami, Arizona and elsewhere in Arizona and in Utah.
Some molybdenum contains from 0.002% to 0.2% rhenium. More than 150,000 troy ounces of rhenium are now being produced yearly in the United States. The total estimated Free World reserve of rhenium metal is 3500 tons. Rhenium metal is prepared by reducing ammonium perrhentate with hydrogen at elevated temperatures.

Isotopes

Natural rhenium is a mixture of two stable isotopes. Twenty six other unstable isotopes are recognized.

Properties

The element is silvery white with a metallic luster; its density is exceeded only by that of platinum , iridium, and osmium, and its melting point is exceeded only by that of tungsten and carbon .
The usual commercial form of the element is powder, but it can be consolidated by pressing and resistance-sintering in a vacuum or hydrogen atmosphere. This process produces a compact shape in excess of 90 percent of the density of the metal.
Annealed rhenium is very ductile, and can be bent, coiled, or rolled. Rhenium is used as an additive to tungsten and molybdenum -based alloys to impart useful properties. 
A Periodic Table of the Elements at Los Alamos National Laboratory