Ferrous sulphate grades are distinguished primarily by hydration state and purity level: food/pharma-grade heptahydrate and dried (exsiccated) monohydrate meet USP/EP or FCC monographs for fortification and pharmaceutical use, while technical and agricultural grades serve water treatment, fertiliser and industrial applications at lower cost and looser purity tolerances. Choosing the right grade depends on the end application's tolerance for insolubles, heavy metals and assay purity.
What Is Ferrous Sulphate?
Ferrous sulphate (iron(II) sulphate, FeSO4) is an inorganic iron salt most commonly encountered as the heptahydrate (FeSO4·7H2O, CAS 7782-63-0), a pale bluish-green crystalline solid. It is also supplied as the monohydrate (FeSO4·H2O, CAS 17375-41-6), a more stable, lower-moisture form often called "dried" or "exsiccated" ferrous sulphate, and less commonly as the anhydrous salt (CAS 7720-78-7). The material is water-soluble, mildly acidic in solution, and readily oxidises to the ferric (Fe3+) state on prolonged exposure to air and moisture, which shows up visually as a shift from green to brown/yellow.
Ferrous Sulphate Grades and Specifications
Buyers should specify grade by intended use rather than assume interchangeability — food, pharma, feed and technical/agricultural grades carry different heavy-metal, assay and insoluble-matter limits.
| Grade | Typical Form | Governing Standard | Common Assay Range | Primary Use |
|---|---|---|---|---|
| Heptahydrate, Food/USP | Green crystals or granules | USP, FCC | ≥98% as FeSO4·7H2O | Food fortification, dietary raw material |
| Monohydrate, Dried/Exsiccated USP | Off-white to buff powder | USP, EP | ≥86% (equivalent FeSO4 basis) | Pharmaceutical formulation |
| Feed Grade | Crystals or powder | Feed-grade specification (assay + heavy metals) | ≥98% | Animal feed mineral premix |
| Technical/Agricultural Grade | Crystals, granules or powder | Technical spec sheet | 90-98% | Water treatment, fertiliser, soil amendment, pigment precursor |
Physical Forms, Packaging and Applications Across Industries
Ferrous sulphate is traded as crystals, granules or fine powder, and occasionally as an aqueous solution for bulk water-treatment users. Standard packaging for crystalline/powder grades is 25 kg PP or PE-lined bags on pallets, with 500-1,000 kg jumbo bags available for technical-grade bulk fertiliser or water-treatment demand; liquid ferrous sulphate is supplied in drums or IBCs. Key application areas include: water and wastewater treatment, where it acts as a coagulant/flocculant and for phosphate removal; agriculture, as a soil and foliar iron micronutrient source and a component of NPK+micronutrient blends; animal feed, as a mineral premix ingredient; food manufacturing, as an iron-fortification ingredient in cereals, flours and beverages; pharmaceutical manufacturing, as a raw material for iron-containing formulations; and industrial uses such as pigment (iron oxide) production and wood preservative formulation.
Handling, Storage and Stability
Ferrous sulphate is hygroscopic and oxidation-sensitive: exposure to moist air converts the pale green Fe2+ salt to brownish-yellow ferric compounds over time, which can affect both appearance and assay. Recommended practice is storage in sealed, moisture-proof packaging in a cool, dry, well-ventilated warehouse, away from strong oxidisers and alkaline materials. Aqueous solutions should be handled in corrosion-resistant equipment, as ferrous sulphate solutions are mildly acidic and can attack unprotected mild steel over time. Standard warehouse conditions are generally sufficient; no special refrigeration is required for solid grades.
Quality Documentation and Sourcing Considerations
For any grade, buyers should request a certificate of analysis (COA) confirming assay (as FeSO4 or elemental Fe), moisture/hydration state, insoluble matter, and heavy-metal limits (particularly lead and arsenic for food/feed/pharma grades), along with a current specification sheet and lot-level traceability documentation. Food, feed and pharmaceutical buyers should confirm the applicable monograph (USP, EP, FCC, or feed-grade specification) is stated explicitly on the COA rather than assumed from the product name. Ferrous sulphate is commonly produced as a byproduct of steel pickling liquor recovery or titanium dioxide manufacturing, so supply characteristics and available grades can vary by regional production source; qualifying more than one supplier per grade is a reasonable sourcing safeguard.
FAQ
What grades of ferrous sulphate are used in food fortification?
Food fortification typically uses the heptahydrate or dried (exsiccated) monohydrate grades meeting FCC or USP monograph requirements, selected based on the required iron content and moisture tolerance of the finished product matrix.
What is the difference between ferrous sulphate heptahydrate and monohydrate?
Heptahydrate (FeSO4·7H2O) contains more bound water and a lower relative iron content per gram than the monohydrate (FeSO4·H2O), which is more stable and less prone to caking, making it preferred in some pharmaceutical and premix applications.
How should ferrous sulphate be stored to prevent oxidation?
Keep it in sealed, moisture-barrier packaging in a cool, dry, well-ventilated area away from oxidising agents; once opened, bags should be resealed promptly to limit air and moisture exposure.
How DIC supports this
DIC stocks ferrous sulphate across multiple grades — food/USP, feed, and technical/agricultural — from regionally qualified sources, with lot-specific COAs and specification sheets available on request. Sensitive food and pharma-grade material is handled through controlled warehouse conditions, and vendor-managed inventory (VMI) arrangements can be set up for high-volume water-treatment or fertiliser blending customers.
