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 formulas CoS, CoS
2, Co
3S
4, and Co
9S
8. In general, the sulfides of cobalt are black,
semiconducting, insoluble in water, and
nonstoichiometric.
[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 (CoS
2) and
linnaeite (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 Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue ...
, 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 , a diminutive form of ''spine,'' in reference to its pointed crystals.
Prop ...
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 nickel to iron ratios (Ni:Fe), but it is usually described as 1:1. In some cases, this ratio is skewed by the presence of pyrrhotite ...
). Mixed metal sulfide minerals include
carrollite (CuCo
2S
4) and
siegenite (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 toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...
. Not only is this reaction useful in the purification of cobalt from its ores, but also in
qualitative inorganic analysis.
[
]
Applications and research
In combination with molybdenum, the sulfides of cobalt are used as catalysts for the industrial process called hydrodesulfurization, which is implemented on a large scale in refineries. 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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