Ferrous carbonate, also known as "siderite" in nature, is slightly soluble in water and soluble in an aqueous solution of carbon dioxide, generating Fe (HCO3) 2. When its solution is exposed to air, excess carbon dioxide escapes, and the precipitated FeCO3 rapidly hydrolyzes and oxidizes, transforming into FeO (OH) precipitation. Strong thermal decomposition generates carbon dioxide and ferrous oxide. In the laboratory, air is isolated and an alkali metal carbonate solution is added to the ferrous salt solution to obtain the product. The product quickly darkens when exposed to air and eventually turns brown FeO (OH). Ferrous carbonate can be used as a flame retardant and an iron additive in animal feed.