Cobalt(II) carbonate

Cobalt(II) carbonate is the inorganic compound with the formula CoCO₃. 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.^[5] Cobalt(II) carbonate also occurs as the rare red/pink mineral spherocobaltite.^[6]

Cobalt(II) carbonate

Co2+ CO32−
Cobalt(II) carbonate powder
Names
IUPAC name Cobalt(II) carbonate
Other names Cobaltous carbonate; cobalt(II) salt
Identifiers
CAS Number	513-79-1 Y 12602-23-2 (cobalt carbonate hydroxide) Y
3D model (JSmol)	Interactive image
ChemSpider	10123 N
ECHA InfoCard	100.007.428
PubChem CID	10565
UNII	7H73A68FUV Y W58TNI7T29 (cobalt carbonate hydroxide) Y
CompTox Dashboard (EPA)	DTXSID7052151
InChI InChI=1S/CH2O3.Co/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2 N Key: ZOTKGJBKKKVBJZ-UHFFFAOYSA-L N InChI=1/CH2O3.Co/c2-1(3)4;/h(H2,2,3,4);/q;+2/p-2 Key: ZOTKGJBKKKVBJZ-NUQVWONBAB
SMILES C(=O)([O-])[O-].[Co+2]
Properties
Chemical formula	CoCO3
Molar mass	118.941 g/mol
Appearance	pink solid
Density	4.13 g/cm3
Melting point	427 °C (801 °F; 700 K) [1] decomposes before melting to cobalt(II) oxide (anhydrous) 140 °C (284 °F; 413 K) decomposes (hexahydrate)
Solubility in water	0.000142 g/100 mL (20 °C)[2]
Solubility product (Ksp)	1.0·10−10[3]
Solubility	soluble in acid negligible in alcohol, methyl acetate insoluble in ethanol
Refractive index (nD)	1.855
Structure
Crystal structure	Rhombohedral (anhydrous) Trigonal (hexahydrate)
Thermochemistry
Std molar entropy (S⦵298)	79.9 J/mol·K[1]
Std enthalpy of formation (ΔfH⦵298)	−722.6 kJ/mol[1]
Gibbs free energy (ΔfG⦵)	−651 kJ/mol[1]
Hazards
GHS labelling:
Pictograms	[4]
Signal word	Warning
Hazard statements	H302, H315, H317, H319, H335, H351[4]
Precautionary statements	P261, P280, P305+P351+P338[4]
NFPA 704 (fire diamond)	2 0 0
Lethal dose or concentration (LD, LC):
LD50 (median dose)	640 mg/kg (oral, rats)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Preparation and structure

Structure of solid cobalt(II) carbonate shown with space-filling ions. Color code: red = O, green = Co, blck = C

It is prepared by combining solutions of cobalt(II) sulfate and sodium bicarbonate:

CoSO₄ + 2 NaHCO₃ → CoCO₃ + Na₂SO₄ + H₂O + CO₂

This reaction is used in the precipitation of cobalt from an extract of its roasted ores.^[5]

CoCO₃ adopts a structure like calcite, consisting of cobalt in an octahedral coordination geometry.^[7]

Reactions

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

CoCO₃ + 2 HCl + 5 H₂O → [Co(H₂O)₆]Cl₂ + CO₂

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).^[8]

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

6 CoCO₃ + O₂ → 2 Co₃O₄ + 6 CO₂

The resulting Co₃O₄ converts reversibly to CoO at high temperatures.^[9]

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: Co₂(CO₃)(OH)₂ and Co₆(CO₃)₂(OH)₈·H₂O.^[10]

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.^[6]

Sodium tris(carbonato)cobalt(III) is a cobalt(III) complex containing three carbonate ligands.

Safety

Toxicity has rarely been observed. Animals, including humans, require trace amounts of cobalt, a component of vitamin B12.^[5]