How pure is alumina produced by the Bayer process?

The Bayer process produces alumina that is considered quite pure, containing only a few hundredths of 1 percent of iron and silicon.1

While the exact composition can vary slightly, purified alumina typically contains the following:

• Residual soda: 0.2 to 0.6 percent1
• Water: 0.5 to 1 percent2
• Other oxides: Less than 0.1 percent2

This high level of purity is essential because any remaining impurities, such as iron oxide, silica, or titania, would contaminate the metal during the subsequent smelting process.2