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Views: 0 Author: Site Editor Publish Time: 2026-08-05 Origin: Site
Magnesium sulfate heptahydrate is a white, crystalline inorganic salt composed of magnesium, sulfur, and oxygen, with seven water molecules bound in its crystal structure. It occurs naturally in mineral deposits (epsomite) and is produced synthetically at industrial scale by reacting magnesium oxide or magnesium carbonate with sulfuric acid.
With a magnesium content of approximately 9.8% and sulfur content of approximately 13%, this highly water-soluble compound serves as a dual-nutrient source — delivering both magnesium and sulfur in a single, cost-effective material. Its solubility (roughly 710 g/L at 20°C) makes it ideal for liquid formulations, fertigation systems, and industrial processes requiring rapid dissolution.
Key physical properties:
Property | Value |
Appearance | White crystals or crystalline powder |
Molecular weight | 246.47 g/mol |
Solubility in water (20°C) | ~710 g/L |
pH (5% solution) | 5.0–8.0 |
Bulk density | 0.8–1.1 g/cm³ (varies by crystal size) |
Melting point | Decomposes at 150°C (loses water of crystallization) |
Magnesium sulfate heptahydrate is available in multiple purity grades, each tailored to specific end-use requirements:
Grade | Typical Purity | Primary Applications |
Agricultural grade | ≥98% | Bulk fertilizer, soil amendment, compound fertilizer blending |
Industrial grade | ≥98% | Textile dyeing, leather tanning, paper manufacturing, water treatment, construction materials |
Feed grade | ≥99% | Animal nutrition, livestock mineral premixes |
Food grade | ≥99.5% | Food additives, brewing, yeast production |
Agriculture accounts for approximately 61% of global magnesium sulfate heptahydrate consumption, making it the dominant downstream sector.
Magnesium sits at the center of the chlorophyll molecule — without it, plants cannot perform photosynthesis. Magnesium-deficient soils produce crops with interveinal chlorosis (yellowing between leaf veins), stunted growth, and reduced yield. Soils particularly prone to magnesium deficiency include:
● Sandy, acidic soils with high rainfall (leaching)
● Intensively farmed soils with heavy potassium application (K⁺ competes with Mg²⁺ uptake)
● Tropical and subtropical soils in high-rainfall regions
Magnesium sulfate heptahydrate provides a rapidly available, water-soluble source of magnesium that plants can absorb immediately — unlike slow-release magnesium sources such as dolomitic limestone.
Crop Category | Examples | Typical Application Method |
High-value economic crops | Citrus, banana, sugarcane, tomato, tea, tobacco, grapes | Foliar spray + soil application |
Field crops | Rice, maize, wheat, soybean, oil palm | Broadcast or fertigation |
Greenhouse crops | Vegetables, flowers, hydroponic crops | Water-soluble fertilizer / nutrient solution |
Turf & ornamental | Golf courses, landscaping, nurseries | Granular broadcast or dissolved spray |
Industrial uses represent approximately 27% of global consumption and are growing at more than 10% annually — significantly outpacing the overall market.
The single largest industrial consumer of magnesium sulfate heptahydrate. MOS boards are non-combustible building materials used for:
● Interior partition walls
● Suspended ceilings
● Fireproof door cores
● HVAC duct insulation panels
● Exterior wall cladding
Growth drivers:
● Stricter building fire safety codes mandating Class A non-combustible materials
● Green building certification programs (LEED, BREEAM) favoring formaldehyde-free materials
● Prefabricated and modular construction demanding lightweight fireproof panels
● MOS boards are environmentally friendly — zero formaldehyde emission, fully recyclable
An emerging, high-growth application. Magnesium sulfate heptahydrate serves as a precursor for magnesium hydroxide (Mg(OH)₂) flame retardants used in:
● Halogen-free low-smoke (HFFR) cable compounds
● Thermoplastic elastomers (TPE/TPO)
● Engineering plastics (polyamide, polypropylene)
● Intumescent coatings for structural steel
The shift away from halogenated flame retardants (brominated, chlorinated) toward mineral-based alternatives is a powerful, regulation-driven trend supporting long-term demand growth.
Magnesium sulfate heptahydrate functions as:
Dyeing auxiliary / mordant:
● Improves dye fixation and color fastness on cotton and silk
Weighting agent:
● Increases fabric weight and improves drape in silk and cotton finishing
Bleaching stabilizer:
● Controls peroxide decomposition in textile bleaching baths
Used in chrome tanning processes as a masking agent and basifying auxiliary — helps achieve uniform chrome distribution and improves leather quality.
Applied as a processing aid in pulp bleaching and paper sizing, contributing to improved paper strength and surface properties.
In industrial cooling water systems and boiler water treatment, magnesium sulfate heptahydrate helps:
● Stabilize water chemistry
● Reduce scaling and corrosion risks
● Provide consistent dosing due to high solubility
Detergent manufacturing:
● Filler and processing aid
Mining chemicals:
● Flotation reagent in mineral processing
Explosives & matches:
● Oxidizer component
Ceramics & porcelain:
● Glaze ingredient
Plastics & rubber:
● Filler and curing agent
Feed-grade magnesium sulfate heptahydrate (purity ≥99%) is an essential magnesium source in animal nutrition premixes. Magnesium is critical for:
● Bone development and skeletal integrity
● Enzyme activation in energy metabolism
● Neuromuscular function and prevention of grass tetany (hypomagnesemia) in grazing cattle
● Eggshell quality in poultry layers
It is included in complete feed formulations and mineral premixes for:
Livestock Type | Typical Application |
Dairy & beef cattle | Prevention of grass tetany, especially on lush spring pasture |
Poultry (broilers & layers) | Bone strength, eggshell quality |
Swine | Growth and metabolic function |
Aquaculture (fish & shrimp) | Osmoregulation and enzyme function |
Q: What is the difference between magnesium sulfate heptahydrate and anhydrous magnesium sulfate?
Magnesium sulfate heptahydrate (MgSO₄·7H₂O) contains seven water molecules and has a magnesium content of ~9.8%. Anhydrous magnesium sulfate (MgSO₄) has no water of crystallization and a magnesium content of ~20%. The heptahydrate form is more commonly used in agriculture and most industrial applications; the anhydrous form is preferred as a desiccant and in applications where water content must be minimized. Approximately two tons of heptahydrate are required to produce one ton of anhydrous product.
Q: Can magnesium sulfate heptahydrate be used in organic farming?
In many jurisdictions, magnesium sulfate from natural mineral sources (mined epsomite) may be permitted in organic production as a soil amendment — subject to certification body approval. Synthetically produced material is generally not permitted. Check with your organic certification agency for specific rules applicable to your market.
Q: What is the shelf life of magnesium sulfate heptahydrate?
When properly stored in sealed packaging in a cool, dry environment, the product is stable for 24 months. However, exposure to humid air will cause caking and gradual loss of free-flowing properties. Once opened, material should be used promptly.
Q: How should I apply magnesium sulfate heptahydrate as fertilizer?
Application rates vary by crop and soil magnesium status. General guidelines:
● Soil broadcast: 50–150 kg/ha
● Foliar spray: 1–2% solution (10–20 g per liter of water), applied at 2–4 week intervals during active growth
● Fertigation: 5–10 kg/ha per application through drip irrigation
Always base application rates on soil test results and local agronomic recommendations.
Q: Is magnesium sulfate heptahydrate hazardous?
The product is classified as non-hazardous under standard transport regulations. It is not flammable, not explosive, and has low acute toxicity. Standard industrial hygiene practices apply: avoid dust inhalation, wear appropriate PPE (gloves, dust mask) when handling bulk quantities.
