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Views: 0 Author: Site Editor Publish Time: 2026-08-05 Origin: Site
Ferrous sulfate heptahydrate (FeSO₄·7H₂O, CAS 7782-63-0) is the most widely traded form of iron(II) sulfate — a blue-green crystalline compound with a global market exceeding USD 2.4 billion. Also known as copperas, green vitriol, or iron(II) sulfate heptahydrate, this versatile inorganic salt powers water treatment plants, boosts crop yields, feeds livestock, and strengthens cement worldwide.
Property | Value |
CAS Number | 7782-63-0 |
Chemical Formula | FeSO₄·7H₂O |
Molecular Weight | 278.02 g/mol |
Common Names | Copperas, Green Vitriol, Iron(II) Sulfate Heptahydrate, Ferrous Sulphate Heptahydrate |
Appearance | Blue-green monoclinic crystals or granular powder |
Iron (Fe) Content | Approximately 19–20% |
Water Solubility | 29.5 g/100 g water at 25°C |
Odor | Odorless |
Understanding the physical chemistry of ferrous sulfate heptahydrate is essential for storage, transport, and formulation work.
Property | Value |
Density | 1.895 g/cm³ |
Melting Point | 60–64°C (decomposes, loses water of crystallization) |
Solubility in Water | 29.5 g/100 mL at 25°C; increases with temperature |
pH (5% solution) | 3.0–4.0 (acidic) |
Crystal Structure | Monoclinic, space group P2₁/c |
Refractive Index | 1.471 |
This is the single largest industrial application of ferrous sulfate heptahydrate, accounting for roughly 35–40% of global demand.
How It Works — Coagulation & Flocculation
When dissolved in water, Fe²⁺ hydrolyzes to form positively charged iron hydroxide species. These neutralize the negative surface charge on suspended colloidal particles (clay, silt, organic matter, microorganisms), causing them to aggregate (coagulation) and settle (flocculation). The net result: crystal-clear effluent water.
Typical dosage rates range from 10–100 mg/L, depending on raw water turbidity.
Specific Water Treatment Functions
Application | Role of FeSO₄·7H₂O |
Municipal drinking water | Primary coagulant, removes turbidity and color |
Industrial wastewater | Removes heavy metals (Cr, Pb, Cd, As), phosphates, and suspended solids |
Textile effluent | Decolorization via reduction of azo dyes |
Electroplating wastewater | Reduces hexavalent chromium Cr(VI) → Cr(III) for precipitation |
Sludge dewatering | Conditions sludge for improved filter press or centrifuge performance |
Odor control (H₂S) | Reacts with dissolved hydrogen sulfide to form insoluble FeS |
Advantages Over Alternatives
Compared to aluminum sulfate (alum) and polyaluminum chloride (PAC):
Lower cost per ton treated
● — ferrous sulfate is a by-product chemical, making it 30–50% cheaper than alum
Broader pH operating range
● — effective at pH 5–9
Simultaneous heavy metal removal
● — reduces Cr(VI) and arsenic without extra chemical addition
Produces denser, faster-settling flocs
● — reduces sludge volume
Iron is an essential micronutrient for all plants — it is a key component of chlorophyll synthesis and numerous enzyme systems. When soil iron is unavailable (common in alkaline or calcareous soils with pH > 7.0), plants develop iron chlorosis: yellowing between leaf veins, stunted growth, and reduced yield.
As a Soil Amendment & Fertilizer
Ferrous sulfate heptahydrate serves dual roles in soil management:
Iron source:
1. Supplies plant-available Fe²⁺ directly to the root zone
Soil acidifier:
2. Lowers soil pH in alkaline soils, improving the availability of iron, manganese, zinc, and phosphorus
Application methods:
Method | Rate | Notes |
Soil incorporation | 5–20 kg per 100 m² | Mix into top 10–15 cm before planting |
Side-dressing | 50–200 g per tree | Apply around drip line, water in thoroughly |
Foliar spray | 0.5–1.0% solution | Fast-acting correction for acute chlorosis |
Lawn conditioning | 15–25 g/m² | Greens turf, suppresses moss; water in after application |
Compost blending | 1–3 kg per m³ | Creates a slow-release iron store lasting 2–3 years |
Crop-Specific Benefits
Citrus & fruit trees:
● Corrects iron chlorosis in alkaline orchard soils; improves fruit color and sugar content
Turf & golf courses:
● Deepens green color (without the rapid growth surge of nitrogen), suppresses silvery thread moss (Bryum argenteum)
Greenhouse vegetables:
● Prevents interveinal chlorosis in tomatoes, peppers, and cucumbers grown in soilless media
Rice paddies:
● Reduces hydrogen sulfide toxicity in flooded soils
Moss Control on Lawns
Ferrous sulfate heptahydrate is one of the most cost-effective moss killers for turf. Applied at 15–25 g/m² as a dry granular or dissolved spray, it desiccates moss within 24–48 hours while simultaneously greening the grass. For severe moss infestations, two applications 4–6 weeks apart provide thorough control.
Iron is a required trace mineral in all livestock and aquaculture diets — essential for hemoglobin synthesis, oxygen transport, and enzyme function. Ferrous sulfate heptahydrate (feed grade) is the most widely used iron source in animal nutrition due to its high bioavailability and low cost.
Feed-Grade Specifications
Parameter | Typical Value |
FeSO₄·7H₂O purity | ≥ 98.0% |
Iron (Fe) content | ≥ 19.7% |
Lead (Pb) | ≤ 15 mg/kg |
Arsenic (As) | ≤ 5 mg/kg |
Cadmium (Cd) | ≤ 10 mg/kg |
Fineness | 95% passing through 40-mesh (425 μm) |
Inclusion Rates by Species
Species | Typical Inclusion (mg Fe/kg feed) | Notes |
Broiler chickens | 80–120 | Higher rates for fast-growing strains |
Laying hens | 60–80 | Supports egg production and shell quality |
Swine (grower-finisher) | 100–150 | Critical for neonatal piglets (low iron reserves) |
Dairy cattle | 50–100 | Supplements forage-based diets |
Aquaculture (fish/shrimp) | 150–300 | Higher demand in intensive systems |
Pet food (dogs/cats) | 80–200 | Standard mineral premix component |
Feed-grade ferrous sulfate heptahydrate is typically supplied as a fine crystalline powder or micro-granule for uniform mixing in premixes and complete feeds.
In Portland cement production, ferrous sulfate heptahydrate serves a critical environmental function: hexavalent chromium (Cr⁶⁺) reduction.
The Problem: Chromium in Cement
Cement clinker naturally contains trace levels of chromium from raw materials and refractory bricks used in kilns. During clinkering, a fraction of this chromium oxidizes to Cr⁶⁺ — a known skin sensitizer and occupational hazard. Wet cement workers exposed to Cr⁶⁺ can develop allergic contact dermatitis ("cement eczema").
The Solution: FeSO₄·7H₂O as a Reducing Agent
Ferrous sulfate heptahydrate reduces soluble Cr⁶⁺ to insoluble, less toxic Cr³⁺:
2CrO₄²⁻ + 6Fe²⁺ + 10H⁺ → 2Cr(OH)₃↓ + 6Fe³⁺ + 2H₂O
Typical addition rates are 0.2–0.5% by weight of cement (2–5 kg per ton), added during finish grinding at the cement mill. The EU Construction Products Regulation (CPR) effectively mandates chromate reduction in bagged cement, making ferrous sulfate a standard additive across European and many Asian markets.
Other Construction Uses
Concrete colorant:
● Produces buff, tan, and reddish-brown hues depending on dosage and oxidation state
Wood preservative:
● Aqueous ferrous sulfate solutions protect timber against fungal decay (traditional "copperas treatment")
Ferrous sulfate has been central to color chemistry for centuries.
Iron Oxide Pigments
FeSO₄·7H₂O is the primary iron source for manufacturing synthetic iron oxide pigments — the largest-volume color pigments globally:
Pigment | Color | Process |
Iron oxide red (PR101) | Reddish-brown | Calcination of FeSO₄ → α-Fe₂O₃ |
Iron oxide yellow (PY42) | Yellow | Precipitation + oxidation → α-FeOOH |
Iron oxide black (PBk11) | Black | Controlled oxidation → Fe₃O₄ |
These pigments are used in paints, coatings, plastics, construction materials, ceramics, and cosmetics — demanding consistent color, high tinting strength, and excellent lightfastness.
Iron Gall Ink
Historically, ferrous sulfate reacted with tannic acid (from oak galls) to produce a deep black iron-tannate complex — the standard writing ink from the Middle Ages through the 19th century. While largely replaced by modern inks, iron gall ink is still used by calligraphers and for archival-quality documents.
Textile Dye Fixative (Mordant)
In natural dyeing, ferrous sulfate acts as a mordant — it binds dye molecules to textile fibers and shifts colors toward darker, more muted tones. Iron mordant transforms:
● Madder red → dusky purple
● Cochineal crimson → charcoal gray
● Logwood purple → deep black
This application remains relevant in artisan textile production and eco-dyeing practices.
Industry | Application |
Metal finishing | Component of iron plating baths; etchant for aluminum anodizing |
Mining | Flotation depressant for sulfide ores; gold cyanidation aid |
Water cooling systems | Corrosion inhibitor in closed-loop cooling towers |
Biogas plants | Hydrogen sulfide (H₂S) scrubbing in anaerobic digesters |
Environmental remediation | In-situ chemical reduction of chlorinated solvents and Cr(VI) in groundwater |
Laboratory reagent | Reducing agent in analytical chemistry; Fenton's reagent component |
Leather tanning | Traditional iron-tannage for black leather |
One of the most common questions from buyers: should I purchase the heptahydrate or the monohydrate form? Both have the same chemical backbone (FeSO₄), but their physical and economic profiles differ significantly.
Parameter | Heptahydrate (FeSO₄·7H₂O) | Monohydrate (FeSO₄·H₂O) |
Appearance | Blue-green crystals/granules | White to yellowish-gray powder/granules |
Iron (Fe) content | ~19–20% | ~29–30% |
Water content | ~45% (7 H₂O molecules) | ~10–12% (1 H₂O molecule) |
Bulk density | ~1.0–1.2 g/cm³ | ~0.8–1.1 g/cm³ |
Flowability | Moderate (may cake) | Good free-flowing powder |
Oxidation stability | Poor — oxidizes readily in air | Good — stable under normal conditions |
Storage temperature | Below 30°C (decomposes at 60–65°C) | Up to 40°C+ |
Price (per metric ton Fe) | Lower unit cost, but higher freight per unit Fe | Higher unit cost, but lower freight per unit Fe |
Dissolution rate | Fast | Moderate (slightly slower) |
Best for | Water treatment, agriculture, cement, short-distance supply | Animal feed premixes, long-distance export, hot-climate storage |
FeSO₄·7H₂O. It contains one iron(II) ion, one sulfate ion, and seven water molecules of crystallization.
Approximately 19–20% elemental iron (Fe) by weight. The exact value depends on purity. Feed-grade material typically guarantees ≥ 19.7% Fe.
Modern production is predominantly as a by-product of two industrial processes: (1) the sulfate-process manufacture of titanium dioxide (TiO₂), where ilmenite ore is digested with sulfuric acid, and (2) steel pickling, where hot-rolled steel is cleaned in sulfuric acid baths. The resulting ferrous sulfate solution is crystallized, centrifuged, and dried.
It depends on the certifying body and country. Some organic standards permit synthetic ferrous sulfate for correcting documented iron deficiency when other methods are insufficient. Always verify with your organic certification agency before application.
6–12 months in original, sealed packaging stored under recommended conditions (cool, dry, below 30°C). Once opened, material should be consumed promptly as exposure to air accelerates oxidation. Oxidized material (brownish discoloration) has reduced efficacy and should not be used for applications requiring Fe²⁺.
Small quantities may be dissolved in water and disposed of via permitted industrial wastewater treatment. Large quantities should be handled through a licensed chemical waste disposal service. Do not discharge directly to surface waters — while not acutely toxic, high concentrations can cause temporary pH depression and discoloration.
Ferrous sulfate contains iron in the +2 oxidation state (Fe²⁺); ferric sulfate contains iron in the +3 oxidation state (Fe³⁺). Ferrous sulfate is a reducing agent (blue-green, water-soluble), while ferric sulfate is an oxidizing coagulant (yellowish, hydrolyzes rapidly). Ferrous sulfate heptahydrate is often used where its reducing power is needed alongside coagulation (e.g., Cr⁶⁺ reduction in cement or wastewater).
Yes. "Copperas" and "green vitriol" are historical names for ferrous sulfate heptahydrate, dating from when it was produced by weathering iron pyrite in open-air beds — a method used from antiquity through the early 20th century.
Brown or yellowish discoloration indicates oxidation — some of the Fe²⁺ has converted to Fe³⁺. This typically results from exposure to moisture, high temperature, or prolonged air contact. While oxidized material may still be usable for some applications (e.g., pH adjustment), its reducing power is compromised, and it should not be used for chromium reduction, water treatment coagulation, or applications requiring active Fe²⁺.
In descending order: (1) water and wastewater treatment, (2) agriculture and horticulture, (3) animal feed, (4) cement manufacturing, (5) pigment production, and (6) various smaller industrial uses.
