The short answer
Zinc sulphate is the zinc salt of sulphuric acid, and it is the standard way of getting soluble zinc into soil, feed and plating baths. It is sold as two hydrates, and the difference between them is the whole commercial story.
- Heptahydrate, ZnSO4·7H2O — about 22.7 % zinc. Large colourless crystals, dissolves fast, cheapest per tonne.
- Monohydrate, ZnSO4·H2O — about 36.4 % zinc. Free-flowing powder or granule, less caking, cheapest per kilogram of zinc delivered.
Buy on zinc content, not on tonnage. A price per tonne comparison between the two forms is meaningless.
Formulas, molecular weights and zinc content
| Form | Formula | CAS | Molecular weight | Zn content |
|---|---|---|---|---|
| Anhydrous | ZnSO4 | 7733-02-0 | 161.47 g/mol | 40.5 % |
| Monohydrate | ZnSO4·H2O | 7446-19-7 | 179.47 g/mol | 36.4 % |
| Heptahydrate | ZnSO4·7H2O | 7446-20-0 | 287.56 g/mol | 22.7 % |
Other names: white vitriol, zinc vitriol, goslarite (the natural heptahydrate mineral). HS code 2833.29. Commercial grades are usually quoted as a minimum zinc percentage — 21 % Zn for standard heptahydrate and 33 % or 35 % Zn for monohydrate are typical fertiliser specifications.
Heptahydrate versus monohydrate
Both are the same salt with different amounts of water of crystallisation, and the monohydrate is simply the heptahydrate dried under controlled conditions. The choice comes down to four things.
- Freight and storage. Heptahydrate is 44 % water by mass. Over any distance you are paying to move water, which is why monohydrate dominates in export fertiliser and feed trade.
- Caking. The heptahydrate effloresces — it loses water to dry air above roughly 30 °C and takes it back up in humidity, and that cycling sets a bag solid. Monohydrate is far more stable in a warehouse and in a blended NPK or feed premix.
- Dissolution. Heptahydrate dissolves quickly and cleanly, which favours it for foliar sprays, fertigation and plating make-up where a rapid, complete solution matters.
- Blending. A dry blend wants a granule that matches the particle size and density of the other components so it does not segregate in the bag. Monohydrate is available granulated for exactly this.
Physical properties
| Property | Value |
|---|---|
| Appearance | Colourless crystals (heptahydrate) or white powder or granule (monohydrate) |
| Odour | Odourless |
| Taste | Astringent, metallic |
| Solubility in water | Very high; heptahydrate roughly 58 g per 100 mL at 20 °C |
| Solubility in ethanol | Slight |
| pH of 5 % solution | Acidic, roughly 4 to 5.5 |
| Behaviour on heating | Loses water of crystallisation stepwise; the anhydrous salt decomposes above about 680 °C |
The mildly acidic solution is worth noting. It is a genuine advantage on alkaline and calcareous soils, where it helps keep the zinc available, and a genuine nuisance in a mixed tank, where it can drop the pH enough to affect other components.
How zinc sulphate is made
The straightforward route is reacting zinc metal, zinc oxide or zinc ash with sulphuric acid, then purifying the liquor and crystallising. A large share of world production starts from secondary material — zinc ash and dross from galvanising, and flue dust — which makes the purification step the thing that separates suppliers.
Secondary feedstock brings lead, cadmium, iron, copper, arsenic and chloride with it. Those are removed by pH adjustment, oxidation and cementation with zinc dust before crystallisation. If that purification is short-cut, the impurities arrive in the bag. This is why a zinc sulphate specification for feed or fertiliser use should always name lead, cadmium and arsenic limits, and not just the zinc percentage — particularly for feed, where cadmium and lead limits are set by regulation in most destinations.
Zinc deficiency and how the sulphate corrects it
Zinc deficiency is among the most common micronutrient disorders in world agriculture. It is worst on high pH and calcareous soils, on sandy and leached soils, on soils high in available phosphate, and on land that has been cropped intensively without micronutrient replacement.
Zinc is required for the synthesis of the auxin indole-3-acetic acid and for a large number of enzymes, so deficiency stunts growth directly. The visible signs are interveinal chlorosis on younger leaves, shortened internodes giving a rosetted habit, and small, narrow leaves. In rice it appears as khaira, with brown blotches and stunting a few weeks after transplanting.
Zinc sulphate corrects it in three ways: broadcast or banded into soil before or at sowing, usually 15 to 25 kg per hectare of heptahydrate depending on soil test; as a foliar spray at roughly 0.5 % solution, often with a little lime to prevent scorch; and as a seed or seedling root treatment. Soil application is longer lasting; foliar is faster and better suited to correcting a deficiency you have already spotted in the field.
Commercial grades and what separates them
| Grade | Typical Zn | What is controlled |
|---|---|---|
| Fertiliser heptahydrate | 21 % min | Zn, free acid, water insolubles, lead, cadmium, arsenic |
| Fertiliser monohydrate | 33 % or 35 % min | Zn, moisture, particle size for blending, heavy metals |
| Feed grade | 33 to 36 % | Regulated heavy metal limits, fluorine, particle size, flow |
| Plating / technical | Per bath spec | Iron, copper, chloride, nickel and organic impurities |
| Pharmacopoeial / AR | Per monograph | Full monograph or trace element profile |
Scapex Exports supplies zinc sulphate heptahydrate fertiliser grade, zinc sulphate monohydrate feed grade, plating grade and technical grade.
Other uses of zinc sulphate
- Animal feed. The standard inorganic zinc source in poultry, cattle and aquaculture premixes, supporting immune function, skin and hoof integrity and growth.
- Electroplating and galvanising. The zinc source in acid zinc plating baths and a component of several passivation and pretreatment systems.
- Viscose rayon. A coagulant in the spin bath, where it controls the rate at which cellulose xanthate regenerates and so determines fibre strength.
- Mineral flotation. A depressant for sphalerite in lead–zinc separation, allowing galena to be floated first.
- Wood preservation and agriculture chemistry. A component of some preservative formulations and a precursor to zinc-based fungicides.
- Pharmaceutical and veterinary. Oral zinc supplementation, astringent solutions and footbath preparations.
Handling, packing and export documents
- Environmental hazard. Zinc sulphate is very toxic to aquatic life. Consignments are frequently shipped as UN 3077, environmentally hazardous substance, solid, n.o.s., Class 9, packing group III. Confirm the classification for your mode and destination before booking, and never allow washings to reach a drain or watercourse.
- Health. Harmful if swallowed; causes serious eye damage and skin irritation. Goggles, gloves and dust extraction when handling open material.
- Segregation. Keep away from strong alkalis, which precipitate zinc hydroxide, and from strong oxidisers.
- Storage. Cool and dry, bags sealed, off the floor. Heptahydrate in particular should be kept out of direct sun and away from heat, which drives efflorescence and caking.
- Packing. 25 kg and 50 kg HDPE laminated bags with inner liner, and 1000 to 1250 kg jumbo bags.
An export consignment should carry a certificate of analysis stating zinc content, moisture, free acid, water-insoluble matter, lead, cadmium, arsenic, iron and particle size distribution; a 16-section GHS safety data sheet; the dangerous goods declaration where the destination requires one; commercial invoice and packing list; certificate of origin; and for feed grade the applicable feed regulation reference with its heavy-metal limits.
Enquire with a specification
Zinc sulphate heptahydrate and monohydrate are supplied by Scapex Exports as a manufacturer and supplier from qualified Indian producers, in fertiliser, feed, plating and technical grades, powder or granular, with certificate of analysis, safety data sheet and full export documentation.
Send the hydrate, minimum zinc content, heavy metal limits, particle size, packing and destination port, and you will get a quotation written against that specification rather than a generic one.
Frequently asked questions
What is the formula of zinc sulphate?
The anhydrous salt is ZnSO4, CAS 7733-02-0, molecular weight 161.47 g/mol. The two commercial forms are the heptahydrate, ZnSO4 7H2O, CAS 7446-20-0, molecular weight 287.56 g/mol, and the monohydrate, ZnSO4 H2O, CAS 7446-19-7, molecular weight 179.47 g/mol.
Which has more zinc, heptahydrate or monohydrate?
Monohydrate, by a wide margin. Zinc sulphate heptahydrate contains about 22.7 % zinc; the monohydrate contains about 36.4 %. One tonne of monohydrate therefore delivers roughly the same zinc as 1.6 tonnes of heptahydrate, which is why fertiliser and feed blends that pay freight over distance normally specify the monohydrate.
What is white vitriol?
White vitriol is the old name for zinc sulphate heptahydrate, the naturally occurring mineral form of which is goslarite. The vitriol names come from the glassy appearance of the crystals - blue vitriol is copper sulphate, green vitriol is ferrous sulphate and white vitriol is zinc sulphate.
Why is zinc sulphate used in agriculture?
Because zinc deficiency is one of the most widespread micronutrient disorders in the world, particularly on calcareous, high pH and heavily cropped soils, and zinc sulphate is the cheapest readily available source. Zinc is needed for auxin synthesis and enzyme function; deficiency shows as interveinal chlorosis, short internodes and small leaves, and in rice as the disorder known as khaira.
Is zinc sulphate hazardous to ship?
It is not flammable or corrosive, but it is toxic to aquatic organisms, so consignments are often classified as an environmentally hazardous substance under UN 3077, Class 9, packing group III. Confirm the classification in force for your mode and destination with your forwarder, and keep the material well away from drains and watercourses.
What is the colour of zinc sulphate?
Zinc Sulphate Heptahydrate is supplied as a white crystalline powder.
What is zinc sulfate?
Zinc Sulphate Heptahydrate (CAS 7446-20-0) is supplied as a white crystalline powder, with the molecular formula H14O11SZn and a molecular weight of 287.56 g/mol. Its main applications include fertilizer, rayon manufacture and feed additive. Scapex Exports exports and supplies it from India in ≥98% Technical grade, with a batch Certificate of Analysis (COA) and MSDS.
Is zinc sulphate soluble in water?
Our product data gives the solubility of Zinc Sulphate Heptahydrate as: solubility in water, g/100ml at 20 °C: 54.
What is the use of zinc sulphate?
The main applications of Zinc Sulphate Heptahydrate are fertilizer, rayon manufacture and feed additive.
Where to buy zinc sulphate?
You can buy Zinc Sulphate Heptahydrate from Scapex Exports, an exporter and supplier based in Ahmedabad, India. Send the grade, quantity and destination port with the Request a Quotation button on the product page and we will confirm availability, packing and price, with the COA and MSDS.