"Bauxite" on a purchase order is never enough. A refinery, a refractory maker and a cement plant will each reject what the others happily buy. The difference is the grade, and grade is defined by chemistry, mineralogy and size.
Metallurgical grade
Metallurgical grade bauxite feeds alumina refineries, which turn it into the alumina that aluminium smelters need. Refiners care about how much alumina they can actually dissolve and how much caustic soda they will lose doing it.
- High Al₂O₃, often 40% or more for refinery feed, with the alumina in an easily digested form such as gibbsite.
- Low reactive silica, because every unit of reactive silica consumes caustic soda and alumina in the process. See why reactive silica matters.
- Consistent lots, so the refinery can hold its digestion conditions steady.
More on our metallurgical grade bauxite page.
Refractory and abrasive grade
Refractory grade is the premium end of the market. The ore is calcined at high temperature to drive off water and form a dense, hard, high-alumina grain used in furnace bricks, castables and abrasives.
- Very high alumina after calcination.
- Low iron and titania, because Fe₂O₃ and TiO₂ act as fluxes that weaken refractories at high temperature.
- Low alkalis and tight control of other impurities.
Only a selected portion of any deposit meets these limits, which is why refractory grade is sorted carefully at the grading stage. Our refractory and abrasive bauxite article goes further, and the product page is here.
Cement grade
Cement plants use bauxite as an alumina corrective in the clinker raw mix, and as a raw material for calcium aluminate cements. They are less demanding on headline alumina but very sensitive to consistency.
- Fe₂O₃ and SiO₂ monitored per lot, because they shift the plant's alumina and silica moduli.
- Predictable moisture and size for smooth handling in raw mill feed.
- Reliable supply, since kilns run continuously.
Read how cement plants use bauxite or see cement grade bauxite.
At a glance
| Grade | Main buyer | Key chemistry | What can disqualify a lot |
|---|---|---|---|
| Metallurgical | Alumina refineries | High available Al₂O₃, low reactive SiO₂ | High reactive silica |
| Refractory & abrasive | Refractory and abrasive makers | Very high Al₂O₃ after calcining | Iron, titania, alkalis |
| Cement | Cement plants | Predictable Fe₂O₃ and SiO₂ | Lot-to-lot swings |
One ore body, several grades
Because weathering is uneven, a single lateritic deposit usually contains material suited to more than one grade. The craft of a bauxite mine lies in separating it: mapping the deposit, planning which benches to mine, then crushing, screening and grading so each lot goes to the buyer it suits. Ore can also be graded to a customer's own specification, agreed per contract and confirmed by lab analysis.