Manganese

March 2, 2011, 2:52 pm
Content Cover Image

Small pieces of manganese, 2-5 mm each. Source: images-of-elements.com

Manganese is gray-white metal with a pinkish tinge, and a very brittle but hard metallic element. Its atomic number is 25. In 1774, while heating the mineral pyrolusite (MnO2, manganese dioxide) in a charcoal fire, the Swedish scientist Johann Gahn discovered manganese. The heat and carbon in the charcoal separated oxygen from the pyrolusite, leaving a metallic manganese residue. This chemical reaction is called a reduction reaction.

caption Manganite. (Source: MII)

Manganese is a reactive element that easily combines with ions in water and air. In the Earth, manganese is found in a number of minerals of different chemical and physical properties, but is never found as a free metal in nature. The most important mineral is pyrolusite, because it is the main ore mineral for manganese. When manganese is alloyed with other metals like aluminum, copper and antimony, the end product is magnetic.

Previous Element: Chromium

Next Element: Iron
25

Mn

54.938
Physical Properties
Color gray-white
Phase at Room Temp. solid
Density (g/cm3) 7.43
Hardness (Mohs) 5
Melting Point (K) 1517.2
Boiling Point (K) 2333
Heat of Fusion (kJ/mol) 14.4
Heat of Vaporization (kJ/mol) 220
Heat of Atomization (kJ/mol) 281
Thermal Conductivity (J/m sec K) 7.81
Electrical Conductivity (1/mohm cm) 5.405
Source Pyrolusite, psilomelane (oxide)
Atomic Properties
Electron Configuration [Ar]4s23d5
Number of Isotopes 30 (1 natural)
Electron Affinity (kJ/mol) ---
First Ionization Energy (kJ/mol) 717.4
Second Ionization Energy (kJ/mol) 1509
Third Ionization Energy (kJ/mol) 3248.3
Electronegativity 1.55
Polarizability (Å3) 9.4
Atomic Weight 54.938
Atomic Volume (cm3/mol) 7.4
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) ---
Atomic Radius (pm) 127
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) 89
Ionic Radius3+ (pm) 75.3
Common Oxidation Numbers +2, +4, +7
Other Oxid. Numbers -3, -2, -1, +1, +3, +5, +6
Abundance
In Earth's Crust (mg/kg) 9.50×102
In Earth's Ocean (mg/L) 2.0×10-4
In Human Body (%) 0.00002%
Regulatory / Health
CAS Number 7439-96-5
OSHA Permissible Exposure Limit (PEL) Ceiling: 5 mg/m3
OSHA PEL Vacated 1989 TWA: 1 mg/m3
Ceiling: 5 mg/m3
STEL: 3 mg/m3
NIOSH Recommended Exposure Limit (REL) TWA: 1 mg/m3
STEL: 3 mg/m3
IDLH: 500 mg/m3
Sources:
Mineral Information Institute
Jefferson Accelerator Laboratory
EnvironmentalChemistry.com
 

Trace amounts of manganese are very important to good health. It makes bones strong yet flexible, and it aids the body in absorbing Vitamin B1. It also is an important activator for the body to use enzymes. As little as 0.00002% Mn in the human body is essential. Studies have shown that a lack of manganese leads to infertility in animals.

Name

The word manganese comes from the Latin word magnes which means magnet.

Sources

Over 80% of the known world manganese resources are found in South Africa and Ukraine. Other important manganese deposits are in China, Australia, Brazil, Gabon, India, and Mexico. The United States imports manganese ore because the manganese resources in the U.S. are relatively low in manganese content per ton of ore. Importing these ores is presently more economical than mining them locally.

Most manganese ore imported to the United States is used to manufacture intermediate manganese ferroalloy products and electrolytic manganese for use in dry-cell batteries. Only a small amount of the ore is directly used in the steel making process.

Some manganese is recovered through the reprocessing of scrap metals and steel slag, or the materials left over from the steel-making process. Though considered waste in terms of its steel content, slag often contains significant amounts of other elements that can be recovered.

Deep-sea nodules of manganese and other metals are scattered on the ocean floor. They form when the hot waters from hot springs (called black smokers) on the ocean bottom meet the cold, deep ocean water. The elements in the hot volcanic waters precipitate as nodules. Though rich in manganese (nearly 25% manganese) they are very deep in the ocean and it would cost too much to make them worth retrieving. This may prove to be an important source of manganese in the future should reserves in the Earth’s crust be depleted and cost-effective deep-sea mining methods are discovered.

Uses

Steel becomes harder when it is alloyed with manganese. It has similar applications when alloyed with aluminum and copper. Hardened steel is important in the manufacture of construction materials like I-beams (24% of manganese consumption), machinery (14% of manganese consumption), and transportation (13% of manganese consumption).

Manganese dioxide is used to: manufacture ferroalloys; manufacture dry cell batteries (it's a depolarizer); to "decolorize" glass; to prepare some chemicals, like oxygen and chlorine; and to dry black paints. Manganese sulfate (MnSO4) is used as a chemical intermediate and as a micronutrient in animal feeds and plant fertilizers. Manganese metal is used as a brick and ceramic colorant, in copper and aluminum alloys, and as a chemical oxidizer and catalyst. Potassium permanganate (KMnO4) is used as a bactericide and algicide in water and wastewater treatment, and as an oxidant in organic chemical synthesis.

Substitutes and Alternative Sources

There are presently no adequate substitutes for manganese in its varied applications.

Further Reading

Glossary

Citation

Institute, M. (2011). Manganese. Retrieved from http://www.eoearth.org/view/article/154436

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