Cobalt sulfide is the name for chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s with a formula Co_xS_y. Well-characterized species include minerals with the formula CoS₂ and Co₃S₄, and the synthetic material Co₉S₈. In combination with molybdenum, the sulfides of cobalt are used as catalysts for the industrial process called hydrodesulfurization

Hydrodesulfurization

Hydrodesulfurization is a catalytic chemical process widely used to remove sulfur from natural gas and from refined petroleum products such as gasoline or petrol, jet fuel, kerosene, diesel fuel, and fuel oils...

, which is implemented on a large scale in refineries

Refinery

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 are as follows:...

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Cobalt sulfides precipitate when aqueous solutions of cobalt(II) ions are treated with hydrogen sulfide

Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

. This reaction is useful in the purification of cobalt from its ores as well as in qualitative inorganic analysis

Qualitative inorganic analysis

Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, so that materials in other forms may need to be brought into this state before using standard...

. In general, the sulfides of cobalt are black, semiconducting, insoluble in water, and nonstoichiometric

Non-stoichiometric compound

Non-stoichiometric compounds are chemical compounds with an elemental composition that cannot be represented by a ratio of well-defined natural numbers, and therefore violate the law of definite proportions. Often, they are solids that contain crystallographic point defects, such as interstitial...

. They react with strong acids to release hydrogen sulfide gas again. They are weak reducing agent

Reducing agent

A reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...

s and can be oxidized to cobalt sulfate.

Minerals

The best defined sulfides of cobalt occur as minerals. The rare mineral cattierite

Cattierite

Cattierite is a mineral found in the Democratic Republic of Congo. It was discovered together with Vaesite by Johannes F. Vaes, a Belgian mineralologist and named after Felicien Cattier, Chairman of the Board, Union Miniere du Haut Katanga....

 has the stoichiometry CoS₂. It is isostructural with iron pyrite

Pyrite

The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...

, featuring disulfide groups, i.e. Co²⁺S₂^2-. Linnaeite

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 ....

, also rare, has the formula Co₃S₄ and crystallizes in the spinel

Spinel

Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety.-Spinel group:...

motif.