Bayerfolyamatból

The Bayer process is a hydrometallurgical technique used primarily for the extraction and refining of aluminum from bauxite ore. Invented by Austrian chemist Karl Josef Bayer, it was patented in 1888. The process involves the digestion of crushed bauxite in a hot solution of sodium hydroxide (caustic soda) under pressure. This alkaline solution dissolves the aluminum-containing minerals, primarily aluminum oxides and hydroxides, forming sodium aluminate.

Impurities present in the bauxite, such as iron oxides, silicon dioxide, and titanium dioxide, are largely insoluble in the sodium hydroxide solution and are separated as a solid residue known as red mud. This red mud is typically disposed of in large ponds. The sodium aluminate solution is then cooled and seeded with aluminum hydroxide crystals. This causes the aluminum hydroxide to precipitate out of the solution.

The precipitated aluminum hydroxide is then filtered, washed, and heated to high temperatures (calcination) in kilns. This process drives off the water molecules, converting the aluminum hydroxide into pure aluminum oxide, also known as alumina. The alumina is then smelted in an electrolytic process, typically the Hall-Héroult process, to produce metallic aluminum. The Bayer process is the principal method used globally for producing alumina, which is the essential precursor for aluminum metal production. The efficiency and environmental impact of the Bayer process are subjects of ongoing research and development, particularly concerning the disposal and potential reuse of the red mud byproduct.