Cobalt has been used as a coloring agent since Bronze Age. It has been found in Egyptian statuettes and in Persian jewelry of the 3 rd millennium BCE. It was also used in China for pottery glazes as early as 618-907 CE. Cobalt in the form of metal was isolated by George Brandt in 1735. In 16 th century kobold name was given to the ores that contain copper but in the end found that ores contain poisonous arsenic. Brandt in 1742 determined that in various ores, the blue color is due to the presence of cobalt. The word kobold derived from German word meaning ‘’goblin ore’’ [1].
| Periodic Table Classification | Group 9 Period 4 |
|---|---|
| State at 20C | Solid |
| Color | Bluish gray metal |
| Electron Configuration | [Ar] 3d7 4s2 |
| Electron Number | 27 |
| Proton Number | 27 |
| Electron Shell | 2, 8, 15, 2 |
| Density | 8.9 g.cm-3 at 20°C |
| Atomic number | 27 |
| Atomic Mass | 58.93 g.mol -1 |
| Electronegativity according to Pauling | 1.88 |
Cobalt is widely present on the earth crust, in combination with other minerals and in natural water. It is the 32 nd most abundant element present on the earth crust. It is present in the sun, in soil, and in bodies of plants and animals. Cobalt is mostly present in combination with nickel. In compound form, it occurs in minerals of in copper and nickel. Most common minerals of cobalt are cobaltite (cobalt sulfoarsenide mineral), linnaeite (sulfide mineral), skutterudite (series of cobalt and nickel mineral), and smaltite (cobalt, nickel arsenide). Cobalt is produced as a byproduct during the mining and refining nickel, silver, lead, copper and iron. Large deposits of cobalt are present in Canada, Australia, Zambia and Brazil.
Refined or polished cobalt is a silvery white metal and have a faint bluish tinge. Its physical properties resemble iron and nickel. Cobalt is a ferromagnetic (strongest magnet), up to 1121 0 C. Its specific gravity is 8.9. Pure cobalt is obtained through smelting process, which is hard and lustrous and release vapors of arsenic. Cobalt is a is transition metal. It melts at 1495 o C and its boiling temperature is 2927 o C [2].
Cobalt is not very reactive metal. It is stable in air and is unaffected by water. Cobalt reacts slowly with dilute acids. It combines with oxygen and produce Co3O4 and lose oxygen at higher temperature (900 o C) and give monoxide (CoO). Cobalt does not catch fire in air and is resistant to burning, unless it is in powder form. Cobalt is weak reducing metal and protected from oxidation by formation of a passivating oxide film. It reacts with halogens and produce halides. Cobalt does not react with hydrogen and nitrogen gas even at high temperatures. At standard temperature it reacts with mineral acids. Cobalt exist in +2 and +3 oxidation state, although -3 to +5 oxidation states compounds are also formed. Cobalt oxides are antiferromagnetic at low temperature. Cobalt (II) oxide has a rock salt structure. In the form of halides, Cobalt (III) fluoride is used in fluorination reaction.
Cobalt is necessary for human as it is a part of essential vitamin, B12. It stimulates the production of red blood cells and is widely used to treat anemia. In work place, when workers are exposed to high level of cobalt, they can suffer from lungs infections such as asthma and pneumonia. When plants grow on the soil near cobalt mining area, they take up high amount of cobalt which may eventually affect human health. The daily intake dose of cobalt is around 1mg.
Cobalt has one stable isotope 59 Co. Cobalt-60 is a commercially important radioisotope that have a half- life of more than 5.2 years [3]. The isotopes of cobalt range in atomic weight from 50 to 73.
[1]. Enghag, Per (2004). “Cobalt”. Encyclopedia of the elements: technical data, history, processing, applications. p. 667. I
[2]. Properties and Facts for Cobalt”. American Elements. Retrieved 2008-09-19.
