Hall–Héroult process

The Hall–Héroult process is the major industrial process for smelting aluminium: alumina, obtained most often from bauxite, is dissolved in molten cryolite and the bath is electrolysed at 940–980 °C, giving metal of 99.5–99.8% purity. It was discovered independently and almost simultaneously in 1886 by the American chemist Charles Martin Hall and the Frenchman Paul Héroult, both 22 years old. Before it, aluminium was made with sodium or potassium and cost more than gold; Hall opened the first large-scale plant in Pittsburgh in 1888, later Alcoa, and with cheaper electric power the metal became an inexpensive commodity. The process uses much electricity and can emit much carbon dioxide.