Rhenium

October 28, 2011, 9:08 pm

Background

caption Rhenium. (Source:University of Texas)

Rhenium is a rare, silvery-white metallic element. Its atomic number is 75 and its symbol is Re. Rhenium was discovered in 1925 by a team of German scientists named Walter Noddack, Ida Tacke-Noddack, and Otto Berg. They discovered rhenium as a trace element in platinum ores and the mineral columbite. It is very dense. It has a melting temperature of 3,186 degrees Celsius (5,767 degrees Fahrenheit). It is not known to have any health benefit for animals or plants. Rhenium does not form minerals of its own, but it does occur as a trace element in columbite, tantalite and molybdenite. These minerals are the principal sources of columbium (commonly called niobium), tantalum and molybdenum metals.

Rhenium is a very rare element that is produced principally as a by-product of the processing of porphry copper-molybdenum ores. Because it is scarce, very little rhenium is actually processed and isolated each year as compared to the millions of tons of copper and millions of pounds of molybdenum that are extracted from these same porphry copper deposits. As a result, the processing of rhenium poses no environmental threat. The equipment that reduces sulfur dioxide in these processing plants also removes any rhenium that may escape through the smokestacks.

Name

Previous Element: Tungsten

Next Element: Osmium
75

Re

186.21
Physical Properties
Color silvery-white
Phase at Room Temp. solid
Density (g/cm3) 21
Hardness (Mohs) ---
Melting Point (K) 3453.2
Boiling Point (K) 5923
Heat of Fusion (kJ/mol) 33.054
Heat of Vaporization (kJ/mol) 707
Heat of Atomization (kJ/mol) 770
Thermal Conductivity (J/m sec K) 48
Electrical Conductivity (1/mohm cm) 51.813
Source Molybdenite (sulfide)
Atomic Properties
Electron Configuration [Xe]6s24f145d5
Number of Isotopes 45 (2 natural)
Electron Affinity (kJ/mol) 14
First Ionization Energy (kJ/mol) 760
Second Ionization Energy (kJ/mol) ---
Third Ionization Energy (kJ/mol) ---
Electronegativity 1.9
Polarizability (Å3) 9.7
Atomic Weight 186.21
Atomic Volume (cm3/mol) 8.9
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) ---
Atomic Radius (pm) 137
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) ---
Ionic Radius3+ (pm) ---
Common Oxidation Numbers +4
Other Oxid. Numbers -3, -1, +1, +2, +3 +5, +6, +7
Abundance
In Earth's Crust (mg/kg) 7.0x10-4
In Earth's Ocean (mg/L) 4.0x10-6
In Human Body (%) 0%
Regulatory / Health
CAS Number 7440-15-5
OSHA Permissible Exposure Limit (PEL) No limits
OSHA PEL Vacated 1989 No limits
NIOSH Recommended Exposure Limit (REL) No limits
Sources:
University of Wisconsin General Chemistry
Mineral Information Institute
Jefferson Accelerator Laboratory
EnvironmentalChemistry.com
 

Rhenium was named after the Greek word for the Rhine River, Rhenus.

Sources

Rhenium is obtained almost exclusively as a by-product of the processing of a special type of copper deposit known as a porphyry copper deposit. Specifically, it is obtained from the processing of the mineral molybdenite (a molybdenum ore) that is found in porphyry copper deposits. A porphyry copper deposit is a valuable copper-rich deposit in which copper minerals occur throughout the rock. The copper in these deposits occurs as primary chalcopyrite (CuFeS2) or the important secondary copper mineral chalcocite (Cu2S).

The identified rhenium resources in the United States are estimated to total 5 million kilograms. These resources are found in the southwestern United States. The identified rhenium resources in the rest of the world are estimated to total 6 million kilograms. Countries producing rhenium include Armenia, Canada, Chile, Kazakhstan, Mexico, Peru, Russia, and Uzbekistan. Even though the United States has significant rhenium resources, the majority of the rhenium consumed in the U.S. is imported. Chile and Kazakhstan provide the majority of the imported rhenium. The rest is imported from Mexico and other nations.

Very small amounts are gathered by recycling molybdenum-rhenium and tungsten-rhenium scrap metals.

Uses

Because of its very high melting point, rhenium is used to make high temperature alloys (an alloy is a mixture of metals) that are used in jet engine parts. It is also used to make strong alloys of nickel-based metals. Rhenium alloys are used to make a variety of equipment and equipment parts, such as temperature controls, heating elements, mass spectrographs, electrical contacts, electromagnets, and semiconductors. An alloy of rhenium and molybdenum is a superconductor of electricity at very low temperatures. These superalloys account for the majority of the rhenium use each year.

Rhenium is also used in the petroleum industry to make lead-free gasoline. In this application, rhenium compounds act as catalysts. (A catalyst is a chemical compound that takes part in a chemical reaction, and can often make the reaction proceed more quickly, but the chemical is not consumed in the chemical reaction.)

Substitutes and Alternative Sources

Substitutes for rhenium as a catalyst are being researched. Iridium and tin have been found to be a good catalyst for at least one reaction. Cobalt, tungsten, platinum and tantalum can be used in some of the other applications for rhenium.

Further Reading



Disclaimer: This article is taken wholly from, or contains information that was originally published by, the Mineral Information Institute. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the Mineral Information Institute should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

Glossary

Citation

Institute, M. (2011). Rhenium. Retrieved from http://www.eoearth.org/view/article/155731

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