Rhenium (75)

Rhenium is silvery white with a metallic lustre; 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. It has other useful properties. It is expensive but useful as a trace alloying agent.

Table: basic information about and classifications of rhenium. •Name: Rhenium
•Symbol: Re
•Atomic number: 75
•Atomic weight: 186.207 (1) 
•Standard state: solid at 298 K
•CAS Registry ID: 7440-15-5
•Group in periodic table: 7
•Group name: (none)
•Period in periodic table: 6 
•Block in periodic table: d-block
•Colour: greyish white
•Classification: Metallic

Historical information
Rhenium was discovered by Walter Noddack, Ida Tacke, and Otto Berg at 1925 in Germany, who announced that they had detected the element in platinum ores and columbite. Origin of name is from the Greek word "Rhenus" meaning river "Rhine". 

Physical properties 
•Melting point: 3459 [or 3186 °C (5767 °F)] K
•Boiling point: 5869 [or 5596 °C (10105 °F)] K
•Density of solid: 21020 kg m-3

Orbital properties
•Ground state electron configuration: [Xe].4f14.5d5.6s2
•Shell structure: 2.8.18.32.13.2
•Term symbol: 6S5/2

Isolation
Commercial rhenium is extracted from molybdenum roaster-flue gas obtained from copper-sulfide ores. Some molybdenum ores contain 0.001% to 0.2% rhenium. Rhenium(VII) oxide and perrhenic acid readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with potassium or ammonium chloride as the perrhenate salts, and purified by recrystallization. Total world production is between 40 and 50 tons/year; the main producers are in Chile, the United States, Peru, and Poland. Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons per year. Prices for the metal rose rapidly in early 2008, from $1000–$2000 per kg in 2003–2006 to over $10,000 in February 2008. The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures:

2 NH4ReO4 + 7 H2 → 2 Re + 8 H2O + 2 NH3