Cobalt(II) carbonate
# Cobalt(II) carbonate

Cobalt(II) carbonate is the inorganic compound with the formula $CoCO_3.$ This reddish 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.

## Preparation and structure

It is prepared by combining solutions cobaltous sulfate and sodium bicarbonate:

    $CoSO_4$ + 2 $NaHCO_3$ → $CoCO_3$ + $Na_2SO_4$ + $H_2O$ + $CO_2$

This reaction is used in the precipitation of cobalt from an extract of its roasted ores.

$CoCO_3$ adopts a structure like calcite, consisting of cobalt in an octahedral coordination geometry.

## Reactions

Like most transition metal carbonates, cobalt carbonate is insoluble in water, but is readily attacked by mineral acids:

    $CoCO_3$ + 2 HCl + 5 $H_2O$ → $[Co(H_2O)_6]Cl_2$ + $CO_2$

It is used to prepare many coordination complexes. The reaction of cobalt(II) carbonate and acetylacetone in the presence of hydrogen peroxide gives tris(acetylacetonato)cobalt(III).

Heating the carbonate proceeds in a typical way for calcining, except that the product becomes partially oxidized:

    6 $CoCO_3$ + $O_2$ → 2 $Co_3O_4$ + 6 $CO_2$

The resulting $Co_3O_4$ converts reversibly to CoO at high temperatures.

## Uses

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.

## Related compounds

At least two cobalt(II) carbonate-hydroxides are known: $Co_2(CO_3)(OH)_2$ and $Co_6(CO_3)_2(OH)_8·H_2O.$

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.

## Safety

Toxicity has rarely been observed. Animals, including humans, require trace amounts of cobalt, a component of vitamin B12.

