Magnesium Oxide: Light-Burned vs Dead-Burned — Choosing by Reactivity, Not by Purity

Purity is the wrong headline

Buyers often compare magnesium oxide offers by MgO percentage alone. But a dead-burned grade with a higher MgO figure can be the wrong product for a feed or fertiliser application, because dead-burning drives off reactivity along with the impurities.

The two families are made for different jobs: light-burned (caustic calcined) magnesia is reactive and is used in feed, fertiliser, chemical and environmental applications; dead-burned (refractory) magnesia is highly fired and is used where heat resistance matters.

What to specify

For a usable comparison, ask each supplier for:

• Manufacturing route — light-burned or dead-burned, stated explicitly
• Loss on ignition, which indicates the degree of calcination in light-burned material
• Reactivity or citric acid activity, where the application depends on it
• Particle size or mesh, since screening drives handling and dosing
• Impurities that matter to you — silica, calcium oxide and iron oxide are the usual ones

Feed and fertiliser buyers: ask about the grade and the documentation

Feed applications have their own limit values and documentation expectations, and fertiliser use is about supplying magnesium to the soil rather than about refractoriness. Tell the supplier the end use and ask for the specification that matches it — a supplier who cannot tell you which grade suits feed should not be quoting for it.

Handle and store with reactivity in mind

Reactive magnesia can take up moisture and carbon dioxide from the air, which changes its behaviour. Storage conditions, packing with a moisture barrier, and shipping time all matter for light-burned material — another reason to buy the grade, not just the percentage.