Metals Masterclass: How is Alumina Produced?

Alumina is the common name for the chemical compound aluminium oxide (Al₂O₃).

Naturally occurring Al₂O₃ is called corundum, and is the foundational component of both rubies and sapphires, whose colour variations arise from impurities in the crystals.

Alumina for industrial use is refined from bauxite ore, which is a mixture of the hydrated aluminium oxide minerals gibbsite, diaspore, and boehmite, along with other compounds such as silicon dioxide, iron oxides, and titanium oxide. Bauxite is often mined from topsoil in tropical and sub-tropical regions, then treated using the Bayer Process - which separates the bauxite into red mud and Al₂O₃, using a combination of heat/pressure and sodium hydroxide. Aluminium hydroxide, in the form of fine-grained crystals, is added to facilitate precipitation of aluminium hydroxide crystals. The hydroxide mixture is then heated to drive off the water, producing several grades of alumina: calcined alumina, smelter grade alumina and activated alumina.

The purified aluminium oxide has many uses - perhaps the best-known being aluminium metal produced in foundries, which is utilised in a variety of applications. Powdered alumina is also employed in several industries - including as fillers in plastic, as an abrasive in grinding applications, in ceramics, and even to produce reflective effects in metallic paints for automobiles. One of the main industrial applications for Al₂O₃ is in refineries, as a catalyst to convert hydrogen sulfide waste gases into elemental sulphur.

As a reference material producer, LGC understands how critical quality checks are at each stage of the production process – from raw bauxite coming out of the ground, to red mud by-products and purity screening of refined alumina. Once the alumina is turned into solid aluminium metal and Al alloys, even more checkpoints are added to the process. LGC Industrial provides numerous 17034 aluminium metal standards typically used with either spark OES or XRF, and we will soon be releasing our own line of powdered bauxite and alumina standards.