The Hall–Héroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium oxide (alumina) (mainly from bauxite, aluminium's chief ore, through the Bayer process) in molten cryolite, and electrolysing the molten salt bath, usually in a purpose-built cell. The Hall–Héroult process applied at industrial scale happens at 940–980 °C and produces 99.5–99.8% pure aluminium. Recycled aluminum requires no electrolysis, thus it does not end up in this process. This process contributes to climate change through the emission of carbon dioxide in the electrolytic reaction.