Cobalt(II) sulfate heptahydrate appears as red monoclinic crystals that liquify around 100 °C and become anhydrous at 250 °C. It is soluble in water, slightly soluble in ethanol, and especially soluble in methanol. The salts are paramagnetic.
It forms by the reaction of metallic cobalt, its oxide, hydroxide, or carbonate with aqueous sulfuric acid.
The hexahydrate is a metal aquo complex consisting of octahedral [Co(H2O)6]2+ ions associated with sulfate anions.
Cobaltous Sulfate is a reddish, toxic, metallic salt. Cobalt sulfate is used in the electrochemical industries, as a drier in paints and inks, as a coloring agent, in storage batteries and as a supplement for Vitamin B12 deficiency. Exposure to cobalt sulfate results in irritation of the skin, eyes and respiratory tract and affects the thyroid, lungs, heart and kidneys. Cobalt sulfate is mutagenic in mammalian cells and is reasonably anticipated to be a human carcinogen based on evidence of carcinogenicity in experimental animals.
Cobalt is obtained from ores via the sulfate in many cases.
Hydrated cobalt(II) sulfate is used in the preparation of pigments, as well as in the manufacture of other cobalt salts. Cobalt pigment is used in porcelains and glass. Cobalt(II) sulfate is used in storage batteries and electroplating baths, sympathetic inks, and as an additive to soils and animal feeds. For these purposes, the cobalt sulfate is produced by treating cobalt oxide with sulfuric acid.
| Items | Standards, % |
| Basis (CoSO4•7H2O) | ≥99-102 |
| Insoluble substance (in water) | ≤0,01 |
| N | ≤0,05 |
| Cl | ≤0,003 |
| Fe | ≤0,005 |
| K+Na | ≤0,03 |
| Ca | ≤0,03 |
| Ni | ≤0,1 |
| Mg | ≤0,005 |
| Zn | ≤0,002 |
| Cu | ≤0,005 |
| pH (5% solution) | 3-5 |