Ferrous sulfate heptahydrate should be a green crystal. Chemically stable when stored. If exposed to air and moisture, some FeSO4 will convert to ferric iron. High free sulfuric acid levels may also cause it to react with other compounds in the feed or mineral mixture. From a feed industry standpoint, the United States is self-sufficient in iron products.
Ferrous sulfate is produced as a by-product of titanium dioxide production.
Titanium dioxide is a pigmenting agent used predominately by the paint industry. A liquid ferrous sulfate-sulfuric acid mixture is produced when the titanium dioxide is extracted from mined ores which contain high iron levels. This mixture is then dried in kilns to produce ferrous sulfate heptahydrate or further dried to produce ferrous sulfate monohydrate. Ferrous sulfate heptahydrate is generally used in swine diets where a premium is placed on biological availability. It must be used at low levels in trace mineral premixes unless lumping is acceptable in the premix product.