Bayer Process

The Bayer process is the principal industrial method for refining bauxite ore into alumina, aluminum oxide, the essential intermediate step before aluminum metal can be produced by electrolysis. The chemist Carl Josef Bayer invented the process in 1888 to solve bauxite's mixed mineral content, typically only 30 to 60 percent aluminum oxide alongside silica, iron oxides and titanium dioxide that earlier methods could not economically separate. The process heats crushed bauxite in a pressure vessel with a hot sodium hydroxide solution at 150 to 200 degrees Celsius, dissolving the aluminum oxide into sodium aluminate while the other minerals remain undissolved and are filtered out as waste; the alumina is then recovered by seeding the solution with high-purity aluminum hydroxide crystals to trigger precipitation, and roughly 90 percent of the resulting gibbsite is converted into aluminum oxide by heating to about 1,470 kelvin in rotary kilns. It remains the cheapest known refining method and still supplies nearly all of the world's alumina, feeding directly into the Hall-Heroult smelting process already documented on this atlas.