calcined alumina

mining

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 22, 2026

Quick Summary

Calcined alumina, also known as aluminum oxide (Al₂O₃), is a white crystalline substance derived from bauxite ore. Bauxite is the primary ore for aluminum and is found near the Earth's surface, making it suitable for open-pit mining.123

The production of alumina from bauxite is a two-step process: refining the ore and then smelting the alumina to produce aluminum. The most common refining method is the Bayer process, which involves crushing bauxite, reacting it with caustic soda, separating impurities (red mud), precipitating aluminum hydroxide, and finally calcining the hydroxide at high temperatures (over 960°C or 1,750°F) to drive off water and produce alumina. Calcined alumina is extremely hard, resistant to chemical attack, and has a high melting point, making it valuable for abrasives, ceramics, and refractories.415

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

6 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

aluminum processing
Aluminum oxide
Calcined alumina is aluminum oxide that has been heated at temperatures in excess of 1,050 °C (1,900 °F) to drive off nearly all chemically combined water. In this form, alumina has great chemical purity, extreme hardness (9 on the Mohs hardness scale, on which diamond…
Read More
Calcined alumina is aluminum oxide that has been heated at temperatures in excess of 1,050 °C (1,900 °F) to drive off nearly all chemically combined water. In this form, alumina has great chemical purity, extreme hardness (9 on the Mohs hardness scale, on which diamond…
Read More