Cobalt [Co]

Characteristics

An: 27 N: 32
Am: 58.933200 g/mol
Group No: 9
Group Name: Transition metals
Period: 4
State: solid at 298 K
Colour: lustrous, metallic, greyish tinge Classification: Metallic
Boiling Point: 3143K (2927°C)
Melting Point: 1768K (1495°C)
Density: 8.90g/cm³

Discovery Information

Who: George Brandt
When: 1737
Where: Sweden

Name Origin

German: kobalt or kobold (evil spirit); Greek: cobalos (mines). "Cobalt" in different languages.

Sources

Occurs in compounds with arsenic, oxygen and sulfur as in cobaltite (CoAsS) and linneite (Co₃S₄). Primary production occurs in Zaire, Morocco, Sweden and Canada. Annual production is around 17 thousand tons.

Abundance

Universe: 3 ppm (by weight)
Sun: 4 ppm (by weight)
Carbonaceous meteorite: 600 ppm
Earth’s Crust: 20 ppm
Seawater: Atlantic surface: n/a ppm; Atlantic deep: n/a ppm; Pacific surface: 6.9 x 10^-6 ppm; Pacific deep: 1.1 x 10^-6 ppm
Human: 20 ppb by weight; 2 ppb by atoms

Uses

Used in many hard alloys; for magnets, ceramics and special glasses. Also used in permanent magnets, razor blades and catalitic converters.
Cobalt compounds have been used for centuries to impart a rich blue colour to glass, glazes, and ceramics. Cobalt has been detected in Egyptian sculpture and Persian jewellery from the third millennium BC, in the ruins of Pompeii (destroyed AD 79), and in China dating from the Tang dynasty (AD 618-907) and the Ming dynasty (AD 1368-1644).
Cobalt-60 is used in cancer therapy, food sterilization and industrial radiography (to detect structural flaws in metal parts).

History

Cobalt compounds have been used for centuries to impart a rich blue colour to glass, glazes, and ceramics. Cobalt has been detected in Egyptian sculpture and Persian jewelry from the third millennium BC, in the ruins of Pompeii (destroyed AD 79), and in China dating from the Tang dynasty (AD 618-907) and the Ming dynasty (AD 1368-1644).
Swedish chemist Georg Brandt (1694-1768) is credited with isolating cobalt sometime between 1730 and 1737. He was able to show that cobalt was the source of the blue colour in glass, which previously had been attributed to the bismuth found with cobalt.
During the 19th century, cobalt blue was produced at the Norwegian Blaafarvevaerket (70-80% of world production), led by the Prussian industrialist Benjamin Wegner. In 1938, John Livingood and Glenn Seaborg discovered cobalt-60.
The word cobalt is derived from the German kobalt, from kobold meaning "goblin", a term used for the ore of cobalt by miners. The first attempts at smelting the cobalt ores to produce cobalt metal failed, yielding cobalt(II) oxide instead; not only that, but because of cobalt’s curious affinity for arsenic, the primary ores of cobalt always contain arsenic, and upon smelting the arsenic oxidized into the highly toxic As4O6, which was breathed in by workers.

Notes

Cobalt in small amounts is essential to many living organisms, including humans. Having 0.13 to 0.30 mg/kg of cobalt in soils markedly improves the health of grazing animals. Cobalt is a central component of the vitamin cobalamin, or vitamin B-12.

Hazards

Cobalt is recognised by NIOSH as a neurotoxic agent.
Powdered cobalt in metal form is a fire hazard. Cobalt compounds should be handled with care due to cobalt’s slight toxicity. 60Co is a powerful gamma ray emitter and exposure to it is therefore a cancer risk.

Cobalt Compounds

Cerulean blue
Cerulean blue is a cerulean (light blue or azure) pigment used in artistic painting. It is particularly valuable for painting atmospheric shades because of the purity of the blue (specifically the lack of greenish hues). The pigment is regarded as permanent: in oil, no other blue pigment retains colour as well.
It was discovered in 1805 by Andreas Hopfner
Cobalt green CoO and ZnO
Cobalt green (Rinmann’s green), is a translucent green pigment made by mixing cobalt(II) oxide and zinc oxide and heating. It was invented by Swedish chemist Sven Rinmann in 1780. Although it is stable and can be safely mixed with other pigments, it is rarely used because it is a weak pigment for its cost.
Cobalt(II) chloride CoCl₂
Because of the dramatic colour change from anhydrous to hydrous and the ease of the reaction, cobalt chloride is used as an indicator of water.
Anyhdrous cobalt chloride is light blue, hydrous cobalt chloride (CoCl₂(H₂O)₆) is bright pink.
Cobalt(II) oxide CoO
A blackish gray powder used extensively in the ceramics industry (earliest examples go back to 12th century Germany) as an additive to create blue coloured (a deep shade called cobalt blue) glazes and enamels as well as in the chemical industry for producing cobaltous salts.
Cyanocobalamin (Vitamin B12) C₆₃H₈₈CoN₁₄O₁₄P
Vitamin B12 is required by many organisms, including humans. Deficiency causes anemia.
Vitamin B12 is naturally found in foods including meat (especially liver and shellfish), eggs, and milk products.

Reactions of Cobalt

Reactions with water
Water has little or no effect on cobalt. However, the reaction of red-hot cobalt and steam produces cobalt(II) oxide.
2Co_(s) + O_2(g) --> 2CoO_(s)

Reactions with air
Cobalt is not very reactive with air. Cobalt will not react directly with nitrogen. Heating will produce cobalt oxide.
3Co_(s) + 4O_2(g) --> 2Co₃O_4(s)
Heating above 900°C will result in cobalt(II) oxide being formed.
2Co_(s) + O_2(g) --> 2CoO_(s)

Reactions with halogens
Cobalt reacts with chlorine, bromine and iodine to form cobalt dihalides.
Co_(s) + Cl_2(g) --> CoCl_2(s)
Co_(s) + Br_2(l) --> CoBr_2(s)
Co_(s) + I_2(s) --> CoI_2(s)

Reactions with acids
Cobalt metal dissolves in dilute sulphuric acid to form solutions containing the Co(II) ion and hydrogen gas.
Co_(s) + H₂SO_4(aq) --> Co²⁺_(aq) + SO₄^2-_(aq) + H_2(g)

Occurrence of Cobalt

Cobalt is not found as a native metal but generally found in the form of ores. Cobalt is usually not mined alone, and tends to be produced as a by-product of nickel and copper mining activities. The main ores of cobalt are cobaltite, erythrite, glaucodot, and skutterudite.
In 2005, the Democratic Republic of the Congo was the top producer of cobalt with almost 40% world share followed by Canada, Zambia, Russia, Brazil and Cuba, reports the British Geological Survey.

Isotopes of Cobalt

⁵⁶Co [29 neutrons] Abundance: synthetic
Half life: 77.27 days [ Electron Capture ]
Decay Energy: 4.566MeV
Decays to ⁵⁶Fe.

⁵⁷Co [30 neutrons]
Abundance: synthetic
Half life: 271.79 days [ Electron Capture ]
Decay Energy: 0.836MeV
Decays to ⁵⁷Fe.

⁵⁸Co [31 neutrons]
Abundance: synthetic
Half life: 70.86 days [ Electron Capture ]
Decay Energy: 2.307MeV
Decays to ⁵⁸Fe.

⁵⁹Co [32 neutrons]
Abundance: 100%
Stable with 32 neutrons

⁶⁰Co [33 neutrons]
Abundance: synthetic
Half life: 5.2714 years [ beta- ]
Decay Energy: 2.824MeV
Decays to ⁶⁰Ni.

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