Cobalt (Co): Properties, Uses, Health & Environmental Effects

Overview

Cobalt is a hard ferromagnetic, silver-white, hard, lustrous, brittle element. It is a member of group VIII of the periodic table and is located between iron and nickel and shares many chemical and physical properties with these two elements.  

Cobalt is found in the Earth’s crust only in a chemically combined form. Cobalt is chemically active, forming many compounds. It is stable in air and unaffected by water, but it is slowly attacked by dilute acids.

The main ores of cobalt are cobaltite, erythrite, glaucodot and skutterdite, but most cobalt is obtained by reducing the cobalt by-products of nickel and copper mining and smelting.  Several methods exist to separate cobalt from copper and nickel, depending on the concentration of cobalt and the exact composition of the used ore.

Cobalt-based blue pigments (cobalt-blue) have been used since ancient times for jewelry and paints and to impart a distinctive blue tint to glass.  Today, cobalt is primarily used in the preparation of magnetic, wear-resistant and high-strength alloys.

What You Need To Know About Cobalt

Discovery

Cobalt was first discovered in 1735 by George Brandt in Stockholm Sweden while working with some ore from a local copper mine. George Brandt showed that it was the presence of unknown element that causes the blue color in glass and not bismuth or other traditional elements, as was commonly believed at the very time.

Initially, chemists were very much skeptical about Brandt’s claims of a new element, but he continued with his research on the mineral and could latter demonstrate his findings that it is indeed an unknown element (Cobalt) that causes blue color in glass.  Eventually, Brandt was given credit for the discovery of the new element.

Occurrence In Nature

Cobalt is of relatively low abundance in the Earth’s crust and in natural waters. The most common ores of cobalt are Smaltite, linnaeite, chloranthite and cobaltite.

The major producers of cobalt in the world market are Zambia, Canada, Russia, Australia, Zaire and Cuba. No cobalt is mined in the United States. The copper belt in the Democratic Republic of Congo (DRC) and Zambia yields averagely 65% of the global cobalt production.

 Periodic Table Facts

• The atomic symbol  of Cobalt on the periodic table of elements is Co
• In the periodic table, Cobalt is located in group 9, period 4, d-block. 
• Cobalt is categorized as a transition metal in the periodic table.
• The atomic number of cobalt is 27. Atomic number is the number of protons.
• The electron configuration of cobalt is [Ar]3d⁷4s²
• The electron per shell of cobalt is 2, 8, 15, 2

Physical Properties

• Cobalt is a hard, silver-white, lustrous, brittle element.
• Cobalt combines with oxygen in the air; however it does not burn unless it is in powdered form.
• Cobalt is a solid at standard temperature and pressure.
• It is ductile but only moderately malleable.
• Cobalt metal has a specific gravity of 8.9.
• Cobalt is one of the three metals that are ferromagnetic at room temperature.
• The melting point of Cobalt is 1768K (1723^oF, 1495^oC).
• Boiling point of Cobalt is 2927^oC (3200K, 5301^oF).
• Density of cobalt is 8.90 grams per cubic centimeter
• The heat of fusion of Cobalt is 16.06 kJ/mol
• The heat of vaporization of Cobalt is 377 kJ/mol
• Cobalt has a Molar heat capacity of 24.81 kJ/mol

Other Properties

• Cobalt is not found as a free element in nature. It is found in mineral ores.  The main ores of cobalt are cobaltite (CoAsS), erythrite (hydrated arsenate of cobalt), glaucodot (Co, Fe)AsS, and skutterudite (Co, Ni)As₃.
• Cobalt is generally produced as a by-product of nickel and copper mining.
• The electrical resistivity and thermal conductivity of cobalt is 62.4nΩ.m (at 20^oC) and 100 W/ (m.k).
• Element cobalt is stable in air and unaffected by water, but is slowly attacked by dilute acids.
• Cobalt has 22 isotopes; the naturally occurring cobalt consists of its one stable isotope, cobalt-59 (⁵⁹Co).
• The atomic weight of Cobalt is 58.9332. Atomic weight is the average mass of the atom.
• Cobalt forms trivalent and pentavalent compounds, the trivalent ones being more common.
• The electronegativity of Cobalt according to the Pauling scale is 1.88.
• The first, second and third Ionization energies of Cobalt is 760.4 kJ/mol, 1648 kJ/mol and 3232 kJ/mol respectively.
• Cobalt has an Atomic radius of 125 pm.
• Cobalt has a hexagonal closed-packed crystal structure.
• Cobalt has high temperature resistance, hardness and wear characteristics when alloyed with other metals.

Reactions

• Cobalt does not react with water at room temperature.
• Cobalt dissolves slowly in dilute mineral acids and does not combine directly with either hydrogen or nitrogen, but will combine on heating with carbon, phosphorus or sulfur.
• Cobalt reacts with most acids to produce hydrogen gas.
• Cobalt is also attacked by oxygen and water vapor at elevated temperatures.
• Cobalt forms two well-defined binary compounds with oxygen, that is, cobaltous oxide (CoO) and tricobalt textroxide or cobalto-cobaltic oxide (Co₃O₄).

Extraction

• Cobalt is produced specifically from one of a number of metallic-lustered ores such as cobaltite.
• Cobalt is usually extracted as a byproduct of mining and refining nickel, silver, lead, copper and iron.
• Industrially, Cobalt is obtained by heating its ores to produce cobalt oxide (Co₂O₃). The compound is then heated with aluminum to free the pure metal.
• Cobalt oxide can be converted to cobalt chloride (CoCl₃).  An electric current is then passed through molten (melted) cobalt chloride to obtain the free element.  

Uses of Cobalt

• Cobalt is primarily used in the preparation of magnetic, wear-resistant and high-strength alloys.
• Cobalt salts were used to decorate ancient Chinese pottery with brilliant blue designs.
• Cobalt metal is used in electroplating because of its attractive appearance, hardness and resistance to corrosion/oxidation.
• Cobalt molybdate (CoMoO₄) is used in the petroleum industry to convert crude oil to gasoline and other petroleum products.  It is also used to remove sulfur from crude oil.
• Cobalt salt is used to produce brilliant colors in paint, porcelain, glass, pottery and enamels.
• Cobalt compounds are commonly used to make colored glass, glazes, paints, rubber, inks, cosmetics and pottery.
• Cobalt is a bio-essential to many living things and is a component of vitamin B₁₂.
• Cobalt is used in samarium-cobalt permanent magnets.
• Radioactive cobalt-60 is used in external beam radiotherapy to sterilize medical supplies and waste.
• The hyrodesulfurization of petroleum uses a catalyst derived from cobalt and molybdenum.
• Cobalt is used as a catalyst in the Fischer-Tropsch process for the hydrogenation of carbon monoxide into liquid fuels.
• Compounds of cobalt like, Lithium cobalt oxide (LiCoO2) is widely used in lithium-ion battery cathodes.
• Other alloys of cobalt are used in jet turbine generators where high-temperature strength is important.
• Cobalt salts can be given to certain animals in small quantities to correct mineral deficiencies.
• Magnetic, wear-resistant and high-strength alloys are chiefly made by cobalt metal.
• Cobalt carboxylates are ordinary catalysts which are also widely utilized in paints, vernishes and binding resins.

Health And Environmental Effect Of Cobalt

Health Effects

• Cobalt is beneficial for humans because it is a part of vitamin B₁₂, which plays an important role in human health.
• Inhalation of cobalt containing dusts from industries may cause allergic dermatitis, rhinitis and asthma.
• Uptake of high concentrations of cobalt is associated with vision problem and heart problems.
• In animals, cobalt is a trace element essential in the nutrition of ruminants (cattle, sheep) and in the maturation of human red blood cells.

Environment Effects of Cobalt

Cobalt occurs naturally in the environment in air, water, soil, rocks, plants and animals. It may also enter air and water and settle on land through run-off when rainwater runs through soil and rock containing cobalt.

Cobalt cannot be destroyed once it has entered the environment. It may react with other particles or adsorb on soil particles or water sediments. Cobalt will only mobilize under acidic conditions, but ultimately most cobalt will end up in soils and sediments.

Summary Of Properties Of Cobalt