Hall-Heroult Process

The Hall-Heroult process is the major industrial method for smelting aluminum, extracting the pure metal by dissolving aluminum oxide in molten cryolite and passing a direct electric current through the mixture at 940 to 980 degrees Celsius to produce metal of 99.5 to 99.8 percent purity. The American chemist Charles Martin Hall and the French chemist Paul Heroult independently discovered the same process in 1886, each only 22 years old at the time. Before their invention aluminum was more valuable than gold or platinum because it was so difficult to extract from ore; combined with the falling cost of electricity, the Hall-Heroult process transformed aluminum into an affordable commodity, and the American Chemical Society designated it a National Historic Chemical Landmark in 1997.