Iron(II) carbonate

Iron(II) carbonate, or ferrous carbonate, is a chemical compound with formula, that occurs naturally as the mineral siderite. At ordinary ambient temperatures, it is a green-brown ionic solid consisting of iron(II) cations and carbonate anions.

Preparation
Ferrous carbonate can be prepared by reacting solution of the two ions, such as iron(II) chloride and sodium carbonate:


 * + →  + 2

Ferrous carbonate can be prepared also from solutions of an iron(II) salt, such as iron(II) perchlorate, with sodium bicarbonate, releasing carbon dioxide:


 * 2 + 2 → + 2 +  +

Sel and others used this reaction (but with instead of 2) at 0.2 M to prepare amorphous.

Care must be taken to exclude oxygen from the solutions, because the  ion is easily oxidized to, especially at pH above 6.0.

Ferrous carbonate also forms directly on steel or iron surfaces exposed to solutions of carbon dioxide, forming an "iron carbonate" scale:



Properties
The dependency of the solubility in water with temperature was determined by Wei Sun and others to be

\log K_{\mathit{sp}} = -59.3498 - 0.041377 T - 2.1963/T + 24.5724 \log T + 2.518 \sqrt{I} - 0.657 I, $$ where T is the absolute temperature in kelvins, and I is the ionic strength of the liquid.

Iron carbonate decomposes at about 500-600 C.

Uses
Ferrous carbonate has been used as an iron dietary supplement to treat anemia. It is noted to have very poor bioavailability in cats and dogs.

Toxicity
Ferrous carbonate is slightly toxic; the probable oral lethal dose is between 0.5 and 5 g/kg (between 35 and 350 g for a 70 kg person).

Iron(III) carbonate
Unlike iron(II) carbonate, iron(III) carbonate has not been isolated. Attempts to produce iron(III) carbonate by the reaction of aqueous ferric ions and carbonate ions result in the production of iron(III) oxide with the release of carbon dioxide or bicarbonate.