Physical Properties
Pink rhombohedral crystals; refractive index 1.855; density 4.13 g/cm3; decomposes on heating; insoluble in water and ethanol; soluble in acids.
Uses
The compound occurs in nature as the mineral cobalt spar or sphaerocobaltite. It is used in ceramics; in cobalt pigments; as a catalyst; as a temperature indicator; and in the preparation of other cobalt(II) salts. It also is added to soil to provide nutritional supplement in forage for cattle.
Preparation
Cobalt carbonate is prepared by heating cobaltous sulfate, cobaltous chloride or any Co2+ salt with sodium bicarbonate in solution:
CoSO4 + NaHCO3→ CoCO3 + NaHSO4
Reactions
Cobalt carbonate dissolves in concentrated HCl or HNO3 when heated, evolving CO2:
CoCO3 + HCl→CoCl2 + CO2 + H2O
It is oxidized by air or weak oxidizing agents, forming cobalt(III) carbonate, Co2(CO3)3. It decomposes on heating, forming the oxides of cobalt with the evolution of CO2.
Toxicity
The compound is moderately toxic by ingestion. (Lewis (Sr.), R. J. 1996. Sax’s Dangerous Properties of Industrial Materials, 9th ed. New York: Van Nostrand Reinhold.)
LD50 oral (rat): 640 mg/kg
Chemical Properties
Cobalt carbonate is Violet Powder. Cobalt (II) carbonate hexahydrate on heating becomes anhydrous by 140 °C while the anhydrous cobalt (II) carbonate decomposes at 427 °C before melting into cobalt (II) oxide.
Uses
Cobalt(II) carbonate is precursor to cobalt carbonyl, cobalt salts and blue pottery glazes such as delftware. It is used as an essential element in dietary supplements and also used in the manufacture of paints and pigments.
Application
Cobalt(II) Carbonate is an inorganic compound that is an intermediate in the hydrometallurgical purification of cobalt from its ore. It is also a paramagnetic solid, an inorganic pigment, and a precursor to catalysts.
Preparation
Cobalt(II) carbonate is prepared by heating cobaltous sulfate, cobaltous chloride or any Co2+ salt with sodium bicarbonate in solution:
CoSO
4 + NaHCO
3 → CoCO
3 + NaHSO
4
Application
Cobalt carbonate is a highly effective colourant used in ceramics as a blue colourant in glazes. It is also a common ingredient in ceramic decals. Cobalt mixed with other colourants such as magnesium and added to glazes produces a more violet/reddish blue colour in oxidation/reduction firings. With this colourant, you can produce blue slips if mixed with white clay bodies. By using this, you can obtain various shades of blue in different intensities. In addition, if mixed with iron and manganese in the right proportions, you can obtain an intense black colour. In general, cobalt is a relatively stable colourant in all kiln atmospheres.
Flammability and Explosibility
Not classified
