Cobalt sulfide is the name for
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
s with a formula Co
xS
y. Well-characterized species include minerals with the formula CoS, CoS
2, Co
3S
4, and Co
9S
8. In general, the sulfides of cobalt are black,
semiconducting
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
, insoluble in water, and
nonstoichiometric
In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...
.
[John D. Donaldson, Detmar Beyersmann "Cobalt and Cobalt Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. ]
Minerals and hydrometallurgy
Cobalt sulfides occur widely as minerals, comprising major sources of all cobalt compounds. Binary cobalt sulfide minerals include the
cattierite
Cattierite (CoS2) is a cobalt sulfide mineral found in the Democratic Republic of Congo. It was discovered together with the nickel sulfide vaesite by Johannes F. Vaes, a Belgian mineralologist and named after Felicien Cattier, who was chairman of ...
(CoS
2) and
linnaeite
Linnaeite is a cobalt sulfide mineral with the composition Co+2Co+32S4. It was discovered in 1845 in Västmanland, Sweden, and was named to honor Carl Linnaeus (1707–1778).
Linnaeite forms a series with polydymite
Polydymite, Ni2+Ni23+S4, is ...
(Co
3S
4). CoS
2 (see image in table) is isostructural with iron
pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
, featuring disulfide groups, i.e. Co
2+S
22−. Linnaeite, also rare, adopts the
spinel
Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals.
Properties
S ...
motif. The Co
9S
8 compound is known as a very rare cobaltpentlandite (the Co analogue of
pentlandite
Pentlandite is an iron–nickel sulfide with the chemical formula . Pentlandite has a narrow variation range in Ni:Fe but it is usually described as having a Ni:Fe of 1:1. It also contains minor cobalt, usually at low levels as a fraction of wei ...
). Mixed metal sulfide minerals include
carrollite
Carrollite, CuCo2S4, is a sulfide of copper and cobalt, often with substantial substitution of nickel for the metal ions, and a member of the linnaeite group. It is named after the type locality in Carroll County, Maryland, US, at the Patapsco m ...
(CuCo
2S
4) and
siegenite
Siegenite (also called grimmite, or nickel cobalt sulfide) is a ternary transition metal dichalcogenide compound with the chemical formula (Ni,Co)3S4. It has been actively studied as a promising material system for electrodes in electrochemical en ...
(Co
3−xNi
xS
4).
CoS is known as jaipurite. However, this species is questionable.
Cobalt sulfide minerals are converted to cobalt via roasting and extraction into aqueous acid. In some processes, cobalt salts are purified by precipitation when aqueous solutions of cobalt(II) ions are treated with
hydrogen sulfide
Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
. Not only is this reaction useful in the purification of cobalt from its ores, but also in
qualitative inorganic analysis
Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find the elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, therefore materials in other forms may ...
.
[
]
Applications and research
In combination with molybdenum, the sulfides of cobalt are used as catalysts for the industrial process called hydrodesulfurization
Hydrodesulfurization (HDS) is a catalytic chemical process widely used to remove sulfur (S) from natural gas and from refined petroleum products, such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils. The purpose of remov ...
, which is implemented on a large scale in refineries
A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value.
Types of refineries
Different types of refineries ar ...
. Synthetic cobalt sulfides are widely investigated as electrocatalysts.
Selected literature
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References
Cobalt sulfide
NIST Webbook
Cobalt(II) compounds
Sulfides
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