Steel ladles, cement kilns, glass furnaces and incinerators all have one thing in common: they are lined with materials that must survive temperatures that would melt most rock. Many of those linings, and many of the grinding wheels and blasting grits used across industry, begin as select high-alumina bauxite.
From raw bauxite to calcined grain
Raw bauxite cannot go straight into a furnace lining. It contains chemically bound water and would shrink and crack when heated. So refractory bauxite is first calcined: fired at high temperature in a rotary or shaft kiln.
During calcination:
- Free moisture and then chemically bound water are driven off.
- The aluminium hydroxides convert to aluminium oxide, ultimately to corundum.
- At high enough temperature the grain sinters into a dense, hard, low-porosity material.
The result, calcined bauxite, has a much higher alumina content than the raw ore because the water is gone. It is then crushed and sized into grains for bricks, castables, ramming mixes and other refractory products.
Why iron and titania are the critical limits
At refractory temperatures, impurities do not just dilute alumina; they actively weaken it.
- Fe₂O₃ and TiO₂ act as fluxes, forming low-melting phases that reduce hot strength and resistance to slag.
- Alkalis (Na₂O, K₂O) and CaO have similar effects.
- SiO₂ combines with alumina to form mullite, which is useful in some products, so silica is controlled rather than simply minimised.
That is why refractory grade is defined by what is not in the ore as much as by its alumina. Only a selected portion of any deposit meets these limits.
Abrasives: brown fused alumina
The abrasive industry takes the process a step further. Calcined bauxite is fused in an electric arc furnace at very high temperature together with a reducing agent such as coke. Much of the iron, silica and titania is reduced and separates out, leaving brown fused alumina, a tough, hard abrasive used in grinding wheels, coated abrasives, blasting media and some refractories.
Fusion is energy-intensive, so feed bauxite with low impurities to begin with means less to remove, less energy and better yield.
What refractory buyers ask for
| Property | Why it matters |
|---|---|
| High alumina (raw and calcined basis) | Determines refractoriness and product class |
| Low Fe₂O₃ and TiO₂ | Prevents fluxing and loss of hot strength |
| Low alkalis and CaO | Avoids low-melting phases |
| Consistent mineralogy | Predictable behaviour during calcination |
| Lump size suited to the kiln | Efficient, even firing |
Selecting refractory ore at the mine
Because refractory limits are tight, selection starts in the pit. Face sampling and grading route the cleanest high-alumina, low-iron material to a separate stockpile, and every lot is tested at the stockpile and again at loading. See crushing, screening and grading.
Minequor supplies select refractory and abrasive grade bauxite from its Raigad mine, with per-lot lab analysis.