Cobalt(II) carbonate is the inorganic compound with the formula CoCO<sub>3</sub>. This pink paramagnetic solid is an intermediate in the hydrometallurgical purification of cobalt from its ores. It is an inorganic pigment, and a precursor to catalysts. Cobalt(II) carbonate also occurs as the rare red/pink mineral spherocobaltite.
It is prepared by combining solutions of cobalt(II) sulfate and sodium bicarbonate:
This reaction is used in the precipitation of cobalt from an extract of its roasted ores.
CoCO<sub>3</sub> adopts a structure like calcite, consisting of cobalt in an octahedral coordination geometry.
Aqueous solutions of cobalt chloride can be prepared from cobalt(II) carbonate with hydrochloric acid according to this idealized equation:
The reaction of cobalt(II) carbonate and acetylacetone in the presence of hydrogen peroxide gives tris(acetylacetonato)cobalt(III).
Heating the carbonate in air (calcining) is accompanied by partial oxidation:
The resulting Co<sub>3</sub>O<sub>4</sub> converts reversibly to CoO at high temperatures.
Cobalt carbonate is a precursor to cobalt carbonyl and various cobalt salts. It is a component of dietary supplements since cobalt is an essential element. It is a precursor to blue pottery glazes, famously in the case of Delftware.
At least two cobalt(II) carbonate-hydroxides are known: Co<sub>2</sub>(CO<sub>3</sub>)(OH)<sub>2</sub> and Co<sub>6</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>8</sub>÷H<sub>2</sub>O.
The moderately rare spherocobaltite is a natural form of cobalt carbonate, with good specimens coming especially from the Republic of Congo. "Cobaltocalcite" is a cobaltiferous calcite variety that is quite similar in habit to spherocobaltite.
Sodium tris(carbonato)cobalt(III) is a cobalt(III) complex containing three carbonate ligands.
Toxicity has rarely been observed. Animals, including humans, require trace amounts of cobalt, a component of vitamin B12.