A practical guide to zinc oxide, why fineness matters more than assay, where it beats zinc sulfate, and how it is supplied, from a US-based distributor.
Zinc oxide (ZnO, CAS 1314-13-2) is a white powder and the highest-analysis common zinc source, at roughly 80% zinc when pure. It is used as a feed supplement, a crop micronutrient, and above all as an activator in rubber vulcanization. It is nearly insoluble in water, so particle fineness governs how available the zinc actually is. Stratus Chemical supplies feed and technical grades across the United States.
| Property | Value |
|---|---|
| Chemical name | Zinc oxide |
| Synonyms | Zinc white, Chinese white, flowers of zinc, zincite |
| CAS number | 1314-13-2 |
| Molecular formula | ZnO |
| Molecular weight | 81.38 g/mol |
| EC / EINECS | 215-222-5 |
| Appearance | White to off-white powder |
| Water solubility | Practically insoluble; soluble in acids and alkalis |
| Grades supplied | Feed grade, technical |
| Packaging | Bags, supersacks |
| Documentation | COA & SDS provided on request |
The figures below are representative of feed and fertilizer grade zinc oxide. 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 |
|---|---|
| Purity (ZnO) | 89.6% min |
| Zinc (Zn) | 72% min |
| Iron (Fe) | 1.0% max |
| Calcium oxide (CaO) | 1.0% max |
| Copper (Cu) | 0.1% max |
| Chlorine (Cl) | 0.05% max |
| Lead (Pb) | 0.04% max |
| Arsenic (As) | 0.01% max |
| Cadmium (Cd) | 0.003% max |
| Fineness, through 80 mesh | 85.0% min |
| Dioxins | 0.75 ng WHO-PCDD/F-TEQ/kg max |
| Packing options | 50 lb bags, big bags / totes |
Zinc oxide is a white, odorless powder produced either by burning zinc vapor in air, which yields the higher-purity direct or French process material, or by roasting zinc-bearing ores and recycled zinc, which yields the indirect or American process product used in bulk industrial and feed applications.
It is nearly insoluble in water but dissolves readily in acids and, being amphoteric, in strong alkalis too. That combination explains most of its behavior: it sits inert in a neutral aqueous environment and becomes available wherever acidity is present, whether that is a digestive tract or an acidic soil.
Buyers habitually compare zinc oxide on ZnO percentage. For most applications that is the less important number.
Because the material does not dissolve, zinc becomes available through surface reaction rather than through going into solution. The rate of that reaction depends on how much surface area is exposed, which is a function of particle size. A finely ground zinc oxide and a coarse one at the identical assay will perform very differently.
This has practical consequences in every market for the product. In soil, a coarse zinc oxide can sit through an entire season without releasing usable zinc. In rubber, fineness affects how efficiently the oxide activates the cure. In feed, it governs how much zinc is actually absorbed rather than passing through. Specifications state this as a percentage passing a given mesh, and it deserves as much attention as the assay line above it.
The largest industrial use by volume. Zinc oxide activates the sulfur vulcanization system, allowing the accelerator to work efficiently, and it also improves heat conduction and aging resistance in the finished compound. Tire and rubber goods manufacturing consumes the majority of world zinc oxide production.
Zinc oxide is a standard zinc supplement in livestock and poultry mineral premixes, supporting immune function, skin and hoof integrity, and growth. It is favored over sulfate sources in feed because the higher analysis reduces the inclusion weight and the freight, and gut acidity solubilizes it adequately.
Finely ground zinc oxide is used to correct zinc deficiency, most effectively on acidic soils where soil acidity dissolves it and on seed and fertilizer coatings where the fine particle sits in intimate contact with the root zone. On neutral and alkaline soils a soluble source usually performs better. See our crop micronutrients guide for how zinc availability changes with pH.
Zinc oxide acts as a flux and opacifier in ceramic glazes and glass, improves durability and mildew resistance in paints, and is used in specialty coatings for its ultraviolet absorption.
| Zinc source | How it behaves | Trade-off |
|---|---|---|
| Zinc oxide | Approximately 72–80% Zn, practically insoluble, dissolves in acid | Lowest freight per unit zinc and excellent in feed, but poorly available in neutral and alkaline soil |
| Zinc sulfate monohydrate | Approximately 35% Zn, fully soluble, dry and blendable | Reliably plant-available across soil types, but roughly twice the tonnage for the same zinc |
| Zinc sulfate heptahydrate | Approximately 22% Zn, dissolves fast in cold water | The choice for tank mixing and fertigation, but the highest freight per unit zinc |
| Chelated zinc (Zn EDTA) | Zinc held in a protective organic complex | Stays available on calcareous and high-pH soils, but several times the cost per unit zinc |
How to choose: the destination decides. For feed, zinc oxide is usually the economical answer because digestive acidity does the solubilizing for you and the freight saving is real. For soil-applied crop nutrition, solubility matters and zinc sulfate is the safer default, with zinc oxide viable on acidic ground provided it is finely ground. On high-pH soils neither oxide nor sulfate holds up well and a chelate is worth costing out. For rubber and ceramics the question is not availability at all but purity and particle size distribution.
Store zinc oxide dry in closed original packaging, off damp floors and away from acids. The material is chemically stable and does not degrade in storage, but fine powder compacts and bridges in hoppers, and damp material cakes.
Dust is the main handling concern. Zinc oxide dust is irritating to the respiratory tract, and inhalation of freshly generated zinc oxide fume, as occurs in welding and hot processing rather than in ordinary powder handling, causes metal fume fever. Use the ventilation and respiratory protection specified in the Safety Data Sheet and avoid dry sweeping.
Zinc oxide is very toxic to aquatic organisms with long-lasting effects. Contain spills and keep material out of drains and surface water.
Zinc oxide is used as a high-analysis zinc supplement in animal feed, as a crop micronutrient, and as an activator in rubber vulcanization, which is its largest industrial market. It also goes into ceramics and glass, coatings, and as a raw material for other zinc compounds. Stratus Chemical supplies feed and technical grades across the United States.
The CAS number for zinc oxide is 1314-13-2. Its molecular formula is ZnO and its molecular weight is 81.38 g/mol. Its EC number is 215-222-5. It is also known as zinc white, Chinese white, flowers of zinc, and in its mineral form as zincite.
Pure zinc oxide is about 80% zinc by weight, the highest analysis of any common zinc source. Commercial feed and fertilizer grades typically run around 89 to 90% ZnO minimum, corresponding to roughly 72% actual zinc. That concentration is more than double zinc sulfate monohydrate, which is why zinc oxide costs far less to freight per unit of zinc.
It depends on whether solubility matters. Zinc oxide carries roughly twice the zinc per ton and costs less to freight, which is why feed mills favor it, since rumen and gut acidity dissolve it readily. For soil-applied crop nutrition zinc sulfate is generally the better choice, because zinc oxide is almost insoluble in water and releases zinc slowly, particularly on neutral and alkaline soils where it may not become available at all within the season. Fineness of grind substantially affects how well zinc oxide performs in soil.
Because zinc oxide is essentially insoluble in water, its availability depends on surface area rather than dissolution. Finer material presents more surface for acids to attack, so it releases zinc faster in soil, in the gut, and in a rubber compound. A coarse zinc oxide applied to soil can pass through a whole season without delivering much zinc at all. Specifications commonly state fineness as a percentage passing a given mesh, and it is a parameter worth reading rather than skipping.
Much commercial zinc oxide is produced from recycled zinc-bearing material, and thermal recycling processes can generate trace dioxins that carry through into the product. Feed grade material therefore commonly carries a dioxin limit, expressed in nanograms of WHO toxic equivalent per kilogram. If the material is going into animal feed, request the dioxin result on the certificate of analysis rather than assuming it was tested.
Stratus Chemical supplies zinc oxide in bags and supersacks, in feed and technical grades, with a certificate of analysis provided for each shipment. Tell us the grade, ZnO assay, fineness, and volume and we will confirm pricing and availability within one business day.
Comparing zinc sources? See zinc sulfate and the crop micronutrients guide, or zinc chloride for metal finishing. Looking for something else? Browse all products or request a quote.
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