Ferrous Sulphate Heptahydrate: The Multifunctional Iron Compound Powering Agriculture And Industry

Ferrous sulphate heptahydrate (FeSO₄·7H₂O), commonly known as copperas or green vitriol, is a blue-green crystalline compound that serves as one of the most important iron supplements and reducing agents. With global production exceeding 3 million metric tons annually, this versatile chemical plays critical roles in agriculture, water treatment, and pigment production, while also being an essential nutrient in animal feed and human health.

Key Properties & Specifications

Physical & Chemical Characteristics

• Molecular Weight: 278.01 g/mol
• Iron Content: 20.1% (elemental Fe²⁺)
• Appearance: Blue-green monoclinic crystals
• Solubility:
  • 256 g/L in water (20°C)
  • Insoluble in alcohol
• Oxidation:
  • Slowly converts to ferric form in air
  • Rapid oxidation above 60°C

Technical Grades

Major Applications

1. Agriculture & Soil Treatment (50% of use)

• Iron Deficiency Correction:
  • 5-20 kg/ha for chlorosis control
  • 2-3x more soluble than ferric forms
• Acidification:
  • Lowers soil pH (0.5 pH unit/ton)
• Case Study: Brazilian soybean farms increased yields 15% with FeSO₄ foliar sprays

2. Animal Nutrition

• Feed Additive:
  • 100-400 mg/kg diet prevents anemia
  • Higher bioavailability than oxide forms
• Pet Food:
  • Essential mineral supplement

3. Water & Wastewater Treatment

• Phosphate Removal:
  • 1.8 mg Fe/mg P precipitation
  • 90-95% efficiency at pH 6.5-7.5
• Odor Control:
  • 50-100 ppm reduces H₂S by 90%

4. Chemical Manufacturing

• Pigment Production:
  • Precursor for iron oxide (Fe₂O₃)
• Fenton’s Reagent:
  • H₂O₂ + Fe²⁺ → hydroxyl radicals
• Wood Preservation:
  • Chromated copper arsenate (CCA) component

5. Emerging Applications

• Battery Materials:
  • Lithium iron phosphate (LiFePO₄) precursor
• 3D Printing:
  • Supports redox-assisted fabrication

Production Methods

1. Titanium Dioxide Byproduct

• Ilmenite Processing:
  • FeTiO₃ + 2H₂SO₄ → FeSO₄ + TiOSO₄
• Yield: 3-4 tons FeSO₄/ton TiO₂

2. Steel Pickling Liquor

• Waste Acid Recovery:
  • Fe + H₂SO₄ → FeSO₄ + H₂
  • Crystallization at 40-50°C

3. Direct Synthesis

• Iron Scrap Dissolution:
  • Fe + H₂SO₄ → FeSO₄ + H₂ (controlled conditions)

Safety & Handling

⚠ Health Considerations:

• Acute Toxicity:
  • LD50 (oral, rat): 1,500 mg/kg
  • Causes GI irritation
• Chronic Exposure:
  • Iron overload risk (hemochromatosis)

✅ Best Practices:

• Storage:
  • Airtight, moisture-proof containers
  • Separate from oxidizers
• PPE:
  • Dust masks, gloves for powder handling
• First Aid:
  • Milk/water for ingestion

♻ Environmental Profile:

• Biodegradation:
  • Rapid oxidation to ferric forms
• Aquatic Impact:
  • LC50 (fish): >100 mg/L

Market Dynamics

Global Production

• Top Producers:
  • China (45%)
  • Venator, Kronos, Verdesian
• Price Range:
  • $150-300/ton (bulk)

Emerging Trends

• Nanofertilizers:
  • Enhanced foliar uptake
• Circular Economy:
  • Increased recovery from industrial byproducts
• High-Purity Demand:
  • Battery material synthesis

Comparison to Alternative Iron Sources

Conclusion

Ferrous sulphate heptahydrate remains the most cost-effective soluble iron source for agricultural and industrial applications. As sustainability initiatives drive waste stream valorization and precision agriculture advances, this ancient compound continues evolving to meet modern challenges—from environmental remediation to next-generation energy storage.