Iron(II) sulfate (ferrous sulfate)

Characteristics

The most common form is the heptahydrate, FeSO4·7H2O, which appears as pale green crystals often called green vitriol. In solution the iron is in the +2 oxidation state, which is more soluble and chemically distinct from ferric (iron(III)) salts. Ferrous sulfate is moderately soluble in water and readily oxidizes to iron(III) species on exposure to air, producing brownish iron oxides.

History and production

Known since antiquity, ferrous sulfate was produced by treating iron-containing materials with sulfuric acid or by weathering sulfide minerals. It was widely used in the past for dyeing, as a mordant, and in the manufacture of iron-gall ink. Industrial production today typically involves neutralizing iron with sulfuric acid or recovering the salt as a byproduct of metal pickling.

Uses and applications

• Medicine: an inexpensive oral iron supplement for treating iron-deficiency anemia.
• Agriculture and horticulture: corrects iron chlorosis in plants and is used to control moss in lawns.
• Industry and water treatment: acts as a reducing agent and coagulant in wastewater treatment and as a precursor to other iron compounds.
• Laboratory and crafts: used as a reagent, in dyeing, and historically in inks and tanning.

Its iron content links it to elemental iron chemistry and many iron-based processes.

Safety and distinctions

Although useful, ferrous sulfate can irritate the skin and gastrointestinal tract and is toxic in large ingestions; proper dosing and storage are essential for supplements. Environmentally, spills can acidify water and elevate dissolved iron. It is important to distinguish ferrous sulfate (Fe2+) from ferric sulfate (Fe3+) and from other iron supplements and salts, as their solubility, color, and reactivity differ.