Manganese Mn

Discovery

Black manganese oxides were among the pigments used in prehistoric cave paintings. Much later, glassmakers added the mineral pyrolusite (manganese dioxide) to molten glass to remove the greenish tint caused by iron, earning it the nickname 'glassmakers' soap'. For centuries pyrolusite was confused with magnetite and with magnesium minerals.

In 1774 the Swedish chemist Carl Wilhelm Scheele showed that pyrolusite contained a new element, although he could not isolate it. That same year his friend Johan Gottlieb Gahn heated manganese dioxide with carbon in a crucible and obtained the metal.

The decisive industrial step came in the nineteenth century, when steelmakers found that manganese removes sulfur and oxygen from molten steel. In 1882 the English metallurgist Robert Hadfield developed a steel containing about 12 percent manganese that hardens as it is struck, still used for railway points and rock crushers.

Origin of the name

The name traces back to magnesia nigra, 'black magnesia', the Latin term for pyrolusite, itself named after the Magnesia region of Greece. Over time the word changed through forms such as manganesum to manganese, which helped distinguish it from magnesium. The symbol is Mn.

Main uses

• Steel: about nine tenths of manganese goes into steel, where it removes sulfur and oxygen and increases strength and hardness.
• Aluminium alloys: manganese improves the corrosion resistance and strength of aluminium, including drink cans.
• Batteries: manganese dioxide is the cathode material in common alkaline and zinc–carbon batteries, and manganese appears in several lithium-ion cathodes.
• Chemicals: potassium permanganate is a strong oxidiser used for water treatment and disinfection.

Isotopes

Manganese has only one stable isotope, manganese-55. The radioactive manganese-53 has a half-life of about 3.7 million years; it is produced by cosmic rays in meteorites and its decay to chromium-53 helps date early solar system events. Manganese-54, with a half-life of about 312 days, is used as a tracer and in calibration. Manganese-52 is being investigated for PET imaging.

In everyday life

The human body needs small amounts of manganese for enzymes involved in bone formation, metabolism and antioxidant defence. Nuts, whole grains, legumes and tea are rich sources, so deficiency is rare.

Long-term inhalation of manganese dust or fumes, for example by miners and welders, can cause manganism, a nervous system disorder with symptoms resembling Parkinson's disease, so workplace exposure is limited.