Iron(II) Sulfate (Ferrous Sulfate) CAS 7720-78-7

Iron(II) Sulfate (Ferrous Sulfate): Properties and Applications

1. Introduction

Iron(II) sulfate (FeSO₄), commonly known as ferrous sulfate or green vitriol, is an inorganic salt with a wide range of industrial, agricultural, and medical applications. It is most commonly encountered as the heptahydrate (FeSO₄·7H₂O), which forms pale green crystals. Its relative low cost, availability, and versatility make it an essential compound in various sectors.

2. Chemical and Physical Properties

Molecular formula: FeSO₄ (anhydrous); FeSO₄·7H₂O (heptahydrate, most common)

Molecular weight: 151.91 g/mol (anhydrous); 278.01 g/mol (heptahydrate)

CAS number: 7720-78-7 (anhydrous); 7782-63-0 (heptahydrate)

Appearance: Pale green to blue-green crystals (heptahydrate); white to grayish powder (anhydrous)

Solubility: Highly soluble in water

Density: 1.898 g/cm³ (heptahydrate); 3.65 g/cm³ (anhydrous)

Stability: Slowly oxidizes on exposure to air, forming ferric sulfate; hygroscopic

3. Synthesis Methods

Industrial production: Typically produced as a by-product of steel pickling (treatment of steel with sulfuric acid) or by direct reaction of iron with sulfuric acid.

Purification: May require removal of impurities, especially when obtained as a by-product.

4. Applications

Water and wastewater treatment: Used as a coagulant to remove suspended solids, phosphates, and heavy metals; also used in sludge conditioning.

Agriculture: Applied as an iron fertilizer to correct iron chlorosis in plants; used as a moss killer and soil acidifier.

Pigment production: Precursor for iron oxide pigments (ochre, red, yellow, black) used in paints, coatings, and construction materials.

Medicine: Used as an iron supplement for treating iron-deficiency anemia; available as oral tablets and liquid formulations.

Chemical industry: Used as a reducing agent, in etching processes, and in the production of other iron compounds.

5. Safety and Toxicology

Skin and eye irritation: May cause irritation upon prolonged contact.

Ingestion: Therapeutic doses are safe; overdosing may cause gastrointestinal irritation, nausea, and toxicity.

Storage: Store in airtight containers away from strong oxidizers and moisture. Protect from air to prevent oxidation.

Regulatory status: Approved for use in food, feed, and pharmaceutical applications within specified limits.

6. Advantages and Limitations

Advantages:

• Cost-effective and widely available.

• Versatile – suitable for agriculture, water treatment, medicine, and pigment production.

• Biologically relevant (source of Fe²⁺).

Limitations:

• Oxidizes on air exposure, losing effectiveness.

• May cause corrosion of equipment.

• Requires careful dosing in medical and agricultural applications.

7. Conclusion

Iron(II) sulfate (FeSO₄) is a versatile and widely used iron salt with essential roles in water treatment, agriculture, pigment production, and medicine. Its heptahydrate form (green vitriol) is the most common commercial grade. While effective and cost-efficient, it requires proper handling and storage to prevent oxidation and maintain its reducing properties. When used within recommended concentrations and guidelines, FeSO₄ provides significant benefits across multiple industries with an acceptable safety profile.