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Carbonyl iron

Carbonyl iron suppliers and sourcing guide

Carbonyl iron is a very pure elemental iron powder made by decomposing iron pentacarbonyl gas, which deposits iron as tiny spheres built up in concentric shells. It is a dark gray, nearly insoluble powder that is almost entirely iron. Brands use it as an iron source in tablets, capsules and flour or cereal fortification, often alongside or instead of reduced and electrolytic iron powders.

See suppliersWhat to ask for on the COA
Also known as
Iron, carbonyl · Elemental iron · Carbonyl iron powder
Facts checked
November 2026

Forms and grades of carbonyl iron

Suppliers sell different products under the same name. Specify the one you need.

  • Standard carbonyl iron

    Fine dark gray powder meeting the Food Chemicals Codex or USP specification.

  • Reduced iron

    A related elemental iron made by reducing iron oxide with hydrogen or carbon monoxide, with coarser, irregular particles.

  • Electrolytic iron

    Elemental iron made by electrodeposition, used mainly for food fortification.

  • Coated grades

    Carbonyl iron with a surface coating for specific tableting or fortification needs.

What to check on the COA

Compare each result with your own specification when the lot arrives.

Iron assay
Total iron by titration after dissolution, usually close to 100%.
Carbon, nitrogen and oxygen
Residual carbon and nitrogen from the carbonyl process and oxygen from surface oxidation.
Particle size
Laser diffraction data; particle size is a key spec for elemental iron.
Acid-insoluble substances
Residue left after dissolving in acid.
Lead, arsenic and mercury
Heavy metals by ICP-MS.

Storage, lots and expiry

Storage and shelf life

Carbonyl iron is stable in dry air but rusts with moisture, so keep it in tightly sealed containers in a dry place. As a fine metal powder it should be handled to limit dust. Shelf life is set by the supplier's specification, with iron assay and appearance the usual retest checks.

Lots and expiry dates

Record iron assay and particle size for each lot and keep carbonyl, reduced and electrolytic iron on separate item codes, because they are not interchangeable in a specification. Check incoming lots for rust-colored particles.

Regulatory status

Facts from regulators and standards bodies, each linked to its source.

  • 21 CFR 184.1375 affirms elemental iron, including carbonyl iron, as GRAS for use in food as a nutrient supplement with no limitation other than current good manufacturing practice.

    Source: ecfr.gov (opens in a new tab)

  • Health Canada's Multi-Vitamin/Mineral Supplements monograph for natural health products lists carbonyl iron among the source ingredients for iron (Table 2).

    Source: webprod.hc-sc.gc.ca (opens in a new tab)

  • 21 CFR 101.17(e) requires dietary supplements in solid oral dosage form that contain iron or iron salts as an iron source to carry a boxed accidental-overdose warning statement.

    Source: ecfr.gov (opens in a new tab)

This is general information, not regulatory advice. Status differs by country and by how the ingredient is used, so check the rules for your product and market.

Carbonyl iron suppliers

Manufacturers and distributors whose own websites say they sell it.

We are checking carbonyl iron suppliers now

Every listing is checked against the supplier’s own website before it goes live, so this list fills in over the coming weeks. The specs and COA checklist above are ready today.

Sell carbonyl iron? Request a listing

Frequently asked questions

What forms of carbonyl iron can brands buy?

Common forms include standard carbonyl iron, reduced iron, electrolytic iron and coated grades. Ask each supplier for the specification sheet of the exact grade they quote.

What should the COA for carbonyl iron include?

Expect iron assay, carbon, nitrogen and oxygen, particle size, acid-insoluble substances and lead, arsenic and mercury, each with its method, specification and result for that lot.

How should carbonyl iron be stored?

Carbonyl iron is stable in dry air but rusts with moisture, so keep it in tightly sealed containers in a dry place. As a fine metal powder it should be handled to limit dust. Shelf life is set by the supplier's specification, with iron assay and appearance the usual retest checks.

What is the regulatory status of carbonyl iron?

21 CFR 184.1375 affirms elemental iron, including carbonyl iron, as GRAS for use in food as a nutrient supplement with no limitation other than current good manufacturing practice. Health Canada's Multi-Vitamin/Mineral Supplements monograph for natural health products lists carbonyl iron among the source ingredients for iron (Table 2). 21 CFR 101.17(e) requires dietary supplements in solid oral dosage form that contain iron or iron salts as an iron source to carry a boxed accidental-overdose warning statement.

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