A practical guide to zinc sulfate, how the monohydrate and heptahydrate forms differ, and when to choose it over a chelate, from a US-based distributor.
Zinc sulfate (ZnSO4, CAS 7446-19-7 monohydrate) is a white, water-soluble zinc salt and the most widely used zinc source in agriculture. The monohydrate carries roughly 35% zinc and suits dry blends and feed; the heptahydrate carries roughly 22% and dissolves faster for foliar and fertigation use. Stratus Chemical supplies both forms in agricultural, feed, and technical grades across the United States.
| Property | Value |
|---|---|
| Chemical name | Zinc sulfate |
| Synonyms | Zinc sulphate, white vitriol, zinc vitriol, sulfuric acid zinc salt |
| CAS number | 7446-19-7 (monohydrate), 7446-20-0 (heptahydrate), 7733-02-0 (anhydrous) |
| Molecular formula | ZnSO4·H2O, ZnSO4·7H2O |
| Molecular weight | 179.47 g/mol (monohydrate), 287.56 g/mol (heptahydrate) |
| EC / EINECS | 231-793-3 |
| Appearance | White to off-white powder, granules, or crystals |
| Zinc content | Approximately 35% (monohydrate), approximately 22% (heptahydrate) |
| Grades supplied | Monohydrate, heptahydrate; agricultural / feed / technical |
| Packaging | Bags, supersacks |
| Documentation | COA & SDS provided on request |
Certificates of analysis are provided with each shipment. Tell us your target zinc assay, hydrate form, and particle size range and we will confirm what is available.
The figures below are representative of feed and fertilizer grade zinc sulfate monohydrate. They are indicative rather than guaranteed: specifications vary by source and by lot, and the certificate of analysis for your material governs.
| Parameter | Typical value |
|---|---|
| Zinc (Zn) | 35.5% min |
| Lead (Pb) | 20 ppm max |
| Iron (Fe) | 20 ppm max |
| Cadmium (Cd) | 10 ppm max |
| Copper (Cu) | 15 ppm max |
| Appearance | White powder |
| Packing options | 50 lb bags, big bags / totes |
Zinc sulfate is the zinc salt of sulfuric acid, supplied commercially as either the monohydrate or the heptahydrate. Both are white, odorless, and readily soluble in water, and both deliver zinc in the sulfate form, which plants and animals take up directly.
Its position in the market comes down to cost per unit of zinc. Zinc sulfate is the cheapest widely available soluble zinc source, and for most soils and most feed formulations it is entirely adequate. More expensive zinc products exist and earn their place under specific conditions, but zinc sulfate is the baseline against which they are judged.
The choice between the two hydrates is the main specification decision, and it is driven by where the material is going.
The monohydrate carries approximately 35% zinc. Because more of each ton is zinc rather than water, it costs less to ship and store per unit of nutrient delivered, and it handles as a dry, free-flowing powder or granule that blends cleanly with dry fertilizer and feed. This is the standard choice for bulk blending and for feed manufacture.
The heptahydrate carries approximately 22% zinc and its advantage is dissolution. It goes into cold water faster and more completely, which matters when a grower is mixing a foliar spray in a tank in the field or dosing a fertigation system. Where the material has to dissolve reliably without agitation and heat, the heptahydrate earns its lower analysis.
The primary use. Zinc deficiency is among the most common micronutrient disorders worldwide, and it shows up strongly in corn, rice, citrus, pecans, and beans, particularly on sandy soils, high-pH soils, and ground that has been levelled or eroded down to subsoil. Zinc sulfate is applied broadcast, banded, in a dry blend, or as a foliar spray to correct it.
Blenders incorporate granular zinc sulfate monohydrate into dry NPK blends to supply zinc alongside the primary nutrients. The heptahydrate goes into liquid fertilizer and fertigation programs where solubility is the governing property. See our crop micronutrients guide for how zinc fits alongside the other micronutrients.
Zinc is an essential trace mineral in livestock and poultry diets, supporting immune function, skin and hoof integrity, and growth. Feed-grade zinc sulfate monohydrate is a standard inclusion in mineral premixes. Feed use requires material meeting the applicable feed-ingredient specification, which is a different product from technical grade.
Outside agriculture, zinc sulfate is used as a depressant in base-metal flotation, as a mordant in textile dyeing, in rayon manufacture, in electroplating baths, and as a raw material for other zinc compounds.
| Zinc source | How it behaves | Trade-off |
|---|---|---|
| Zinc sulfate monohydrate | Approximately 35% Zn, fully soluble, dry and blendable | Lowest cost per unit zinc, but zinc can tie up on high-pH soils |
| Zinc sulfate heptahydrate | Approximately 22% Zn, dissolves fast in cold water | Best for tank mixing and fertigation, but more freight per unit of zinc |
| Zinc oxide | High zinc analysis, low water solubility | Cheap per unit zinc and common in feed, but poorly available to plants unless finely ground and acidified |
| Chelated zinc (Zn EDTA) | Zinc held in a protective organic complex | Stays plant-available on calcareous and high-pH soils, but several times the cost per unit zinc |
How to choose: soil pH decides it. Below roughly neutral, zinc from sulfate stays available and the chelate is difficult to justify economically. On calcareous or high-pH ground, a large share of applied sulfate zinc converts to forms the plant cannot reach, and the chelate delivers enough more of what you apply to pay for itself. The other decision point is method. If the product has to dissolve in a spray tank, the heptahydrate; if it goes into a dry blend or a feed mill, the monohydrate.
Store zinc sulfate dry, in closed original packaging, off damp floors. Both hydrates are hygroscopic to a degree, and bags that take on moisture will cake and become difficult to blend or meter accurately.
The heptahydrate additionally effloresces, meaning it slowly loses water of crystallization in warm dry air and can shift toward a lower hydrate over time. Keep it sealed and out of heat if the analysis matters to your formulation.
Zinc sulfate is toxic to aquatic life, so contain spills and prevent material from reaching drains, ditches, or surface water. Handle dust with the respiratory and eye protection specified in the Safety Data Sheet, and avoid dry sweeping.
Zinc sulfate is used primarily as a soluble zinc source in agriculture, correcting zinc deficiency through soil application, fertilizer blends, foliar sprays, and fertigation. It is also used as a zinc supplement in animal feed, and in industrial applications including mineral flotation, textile processing, and water treatment. Stratus Chemical supplies monohydrate and heptahydrate forms in agricultural, feed, and technical grades across the United States.
Zinc sulfate has a different CAS number for each hydrate. The monohydrate is 7446-19-7, the heptahydrate is 7446-20-0, and the anhydrous form is 7733-02-0. All share EC number 231-793-3. Molecular weights are 179.47 g/mol for the monohydrate, 287.56 g/mol for the heptahydrate, and 161.44 g/mol anhydrous.
The difference is water of crystallization, and it drives zinc concentration. Monohydrate carries roughly 35% zinc; heptahydrate carries roughly 22%, because more of its weight is water. Monohydrate is the standard choice for dry fertilizer blends and animal feed, since it delivers more zinc per ton shipped and handles well as a free-flowing powder or granule. Heptahydrate dissolves more readily in cold water, which favors foliar sprays, fertigation, and any application mixed on site.
Zinc sulfate monohydrate contains approximately 35% zinc and heptahydrate approximately 22%, based on the stoichiometry of the pure compounds. Commercial grades vary slightly around those figures depending on assay and moisture, so always work from the guaranteed analysis on the certificate of analysis for the specific lot rather than a theoretical value.
Zinc sulfate costs considerably less per unit of zinc and performs well on neutral and acidic soils where the zinc stays available to the plant. Chelated zinc, such as zinc EDTA, holds the zinc in a protected form that resists tie-up on high-pH and calcareous soils, so it delivers more of what you apply under those conditions but costs more per unit of zinc. On high-pH soils the chelate often justifies its price; on lower-pH soils it usually does not.
Zinc sulfate monohydrate is widely used as a zinc supplement in animal feed. Feed use requires a product that meets the applicable feed-ingredient specification, which is distinct from agricultural or technical grade material. Specify feed grade explicitly when ordering and request the documentation covering the grade so you can confirm it against your own requirements.
A representative feed and fertilizer grade zinc sulfate monohydrate specification runs zinc at 35.5% minimum, with lead and iron each at 20 ppm maximum, cadmium at 10 ppm maximum, and copper at 15 ppm maximum, supplied as a white powder. Specifications vary by source and lot, so confirm against the certificate of analysis for the material you are quoted.
Stratus Chemical supplies zinc sulfate in bags and supersacks, in monohydrate and heptahydrate forms and in agricultural, feed, and technical grades, with a certificate of analysis provided for each shipment. Tell us the hydrate form, grade, particle size, and volume and we will confirm pricing and availability within one business day.
Building a micronutrient program? See copper sulfate and the crop micronutrients guide, or the full agriculture range. Looking for something else? Browse all products or request a quote.
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