Britannica Sources used in this answer

How does calcination turn aluminum hydroxide into alumina?

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

aluminum processing Rolls of processed aluminum.

In the Bayer process, calcination is the final stage used to transform aluminum hydroxide into alumina (aluminum oxide).1

The process involves heating the filtered and washed aluminum hydroxide crystals in rotary kilns or stationary fluidized-bed flash calciners at temperatures exceeding 960 °C (1,750 °F). During this intense heating, both free water and chemically combined water are driven off. This thermal treatment removes the water content, leaving behind commercially pure alumina—a dry, fine, white powder.12