Aluminum Discovery and Extraction – A Brief History
The term aluminum comes from the alum compound, (KAl(SO4)2∙12H2O), which contains it. In 18th century it was realized that alum contained a peculiar base, different from all others, but only in the 19th century scientists were able to isolate it.
Berzelius and Davy tried to use electrolysis processes to isolate the metal contained in alumina. In particular Davy heated a mixture of alumina and potash and then submitted the mix to a electrical current, but with no success.
In 1825 was Oersted to try to isolate the metal believed to be contained into the alumina. He first prepared anhydrous aluminum chloride (AlCl3) by passing a current of chlorine over a mixture of charcoal and alumina heated to redness. Then, the aluminum chloride produced was mixed and heated with potassium amalgam producing potassium chloride and aluminum amalgam. Distillation of this amalgam without contact with the atmosphere left a lump of metal which color, said Oersted, resembles tin in color and sheen.
Wöhler repeated the Oersted experiment, but was unable to duplicate the results. Recent repetitions of the experiment, based on Oersted notes, have shown that using a very dilute potassium amalgam (1.5% K) it is possible to extract the aluminum.
Oersted encouraged Wöhler to continue in his attempts. So, Wöhler first produced the anhydrous aluminum chloride. Then, he put in a platinum crucible a mixture of AlCl3 and potassium (K), instead of using potassium amalgam as Oersted. The crucible was closed and some heat applied just to start the reaction. Soon, the crucible became very hot, being the reaction:
exothermic. The produced aluminum was contaminated with platinum, so he repeated the experiment with porcelain and other materials crucibles, always being able to produce aluminum in the form of a gray powder. The aluminum produced was contaminated by potassium, platinum or aluminum chloride, however he first described the most important properties of aluminum and then, in 1845, was able to produce a coherent mass of aluminum.
In 1855 French scientist Henri Sainte-Claire Deville, ignoring Wöhler 1845 experiment, duplicated it. Observing the aluminum chloride reduction, he understood the importance of the discovery and immediately started to study how to produce large quantities of this metal to be commercialized. Two ways were possible. The first one was the chemical production of the aluminum, using the chloride as salt and the potassium as the agent to reduce it, the second choice was an electrolytic method to reduce the chloride, with a carbon anode and a platinum cathode. Both methods were difficult to implement on a large scale. In the chemical method, the potassium was very expensive and dangerous to manipulate, while there were not available sources of electricity at low cost, the only one existing being primary batteries. Hence, H. St.Claire Devile choose the chemical method to produce aluminum, using as reduction agent the most common in nature sodium (Na) rather than potassium. The Deville’s work was greatly helped by the funds gave him by Napoleon III. Thanks to the work of other chemists of that time, Deville was able to produce for himself large quantities of sodium. At the same time in this period two other processes had to be converted into industrial processes, the first one being the production and refining of alumina and the second one the conversion of alumina into aluminum chloride. Anyway, in 1859 the available quantity of aluminum increased (2 tons/year produced in Salindres plant). Through the years going from 1855 to 1890 the aluminum price declined from the equivalent 1200 €/kg to 13 €/kg. During that years, different chemical and electrochemical methods were developed for the aluminum extraction. Chemical methods were more or less variations around the basic St. Claire Deville process. We can mention: Castner, Netto, Grabau, Webster, Frismuth, etc…The electrochemical processes could be splitted into two main categories: electrothermic and electrolytic. For the electrothermic processes we can mention Cowles, Héroult, Brin, Bessemer, Stefanite, Moissan, while for the electrolytic processes we have Héroult, Adolphe Minet, Hall, Hampes, Kleiner, Gooch, Waldo.
From all these processes, emerged the work of the American Charles Martin Hall and French Paul Louis Toussaint Héroult, whom independently and at the same time invented the process that is still used to reduce alumina to aluminum.
In 1880 at the Oberlin College near Cleveland, Ohio, two people met. One was Frank Fanning Jewett, professor of chemistry and mineralogy at the Oberlin College. Jewett had the possibility to study at the University of Göttingen in Germany between 1873 and 1875. During his stay in Germany he met Wöhler, who had isolated aluminum in 1827. The other was a young student from Oberlin, Charles Martin Hall, self-educated person in chemistry and so passionate to conduct experiments at his home. Hall, at the age of 16, already knew the problems involved in the aluminum production and, under the Jewett guidance and encouragement, worked on aluminum chemistry both at home and Oberlin College laboratory. Hall first tried chemical reduction methods to produce aluminum, but with no results. Then, together with Jewett, they decided to follow the electrolytic way to produce aluminum. In a first attempt, Hall tried to decompose aluminum fluoride (AlF3) dissolved in water, but the only results was the production of hydrogen at the anode and aluminum hydroxide at the cathode. The important thing in this work was the selection of the fluoride, never tried before. The next step was the use of fused salts as solvents. After different experiment, he choose the cryolite as the solvent, being him and Jewett aware of its use in the Deville works. He was able to melt cryolite and showed that it was a good solvent for alumina. The first electrolysis attempt was made using a clay crucible, but the result was the production of silicon from the crucible material. Then, recognizing this, the clay crucible was lined with graphite, it was added some aluminum fluoride to the cryolite in order to lower the melting point and the experiment was repeated. After several hours of electrolysis, he cooled the melt and broke it open, finding small silvery globules that Jewett confirmed to be aluminum. It was February, 23rd 1886.
After some troubles, in 1888 a group of investors, organized by Captain Alfred Hunt, provided Hall with enough fund to establish the Pittsburgh Reduction Company, the Alcoa predecessor.
One or two months later the Hall discovery, French Paul Louis Toussaint Héroult made the same discovery independently. He learned of the St.Claire Deville discoveries at the age of 15 reading the Deville’s famous treatise. He tried to produce aluminum electrolyzing various aluminum compound, with no success. Then, he tried to electrolyze cryolite. During the process, he find the iron cathode was melted. Because the temperatures were not so high to justify a melting of the iron, he realized that some alloy had been formed. Few days later, in an attempt to lower melt temperature he added some sodium aluminum chloride and noticed that the carbon anode was consumed. What happened was that the sodium aluminum chloride entered in contact with the moisture, being converted into hydrated alumina. So, basically Héroult discovered the same process to produce aluminum revealed by Hall just a couple of months before.