Aluminum

As a highly reactive metal, aluminum is very difficult to separate from the other elements that are combined with it in its minerals and compounds. In spite of its great abundance on Earth, the metal itself remained unknown for centuries. In 1825, some impure aluminum metal was finally isolated by H. C. Oersted by treating aluminum chloride, AlCl₃, with potassium amalgam—potassium dissolved in mercury. Then in 1827, H. Wöhler obtained pure aluminum by the reaction of metallic potassium with AlCl₃. He is generally given credit for the discovery of this element.

But it was still very expensive to produce aluminum metal in any quantity, and for a long time it remained a rare and valuable metal. In 1852, aluminum was selling for about $545 a pound. The big breakthrough came in 1886, when Charles M. Hall, a 23-year-old student at Oberlin College in Ohio, and Paul L-T. Héroult, another college student in France, independently invented what is now known as the Hall or Hall-Héroult process. It consists of dissolving alumina in melted cryolite, Na₃AlF₆, a common aluminum-containing mineral, and then passing an electric current through the hot liquid. Molten aluminum metal collects at the cathode (negative electrode) in a process called electrolysis. Not long after the development of this process, the price of aluminum metal plummeted to around 30 cents a pound.

In the production of aluminum today by the Hall-Héroult process, the aluminum oxide is dissolved in a molten mixture of sodium, calcium, and aluminum fluorides, which melts at a lower temperature than cryolite. The aluminum oxide is in the form of bauxite, a white, brown, or red earthy clay; it was first found near Les Baux, France, in 1821 by P. Berthier, and is now the main source of all aluminum. It is mined in various parts of Africa and in France, Surinam, Jamaica, and the United States—mainly in Alabama, Arkansas, and Georgia. The world's supply of bauxite appears to be immense enough to last for hundreds of years at the rate it is being mined today.