Aluminum is one of the most modern metals if we compare it to metallurgy born more than 5000 years ago. It was at the beginning of the nineteenth century when a Danish chemist Hans Christian Oersted isolated the metal for the first time in 1825 by means of a chemical process that used an amalgam of potassium and aluminum chloride.
In 1827, the German chemist Wöhler obtained it in powder form by reacting potassium with aluminum chloride and later in 1845, he himself determined for the first time the properties of the newly discovered metal, density and lightness and separated it into pellets.
Aluminium is extremely abundant in the composition of the Earth’s crust (and on the moon), it is found in an approximate proportion of 15% and only silica exceeds it.
The most significant industrial mineral is “bauxite” with a content between 55 and 65 of alumina (aluminum oxide Al2O3), which is mainly located in the tropical zone. This mineral was discovered by M. Pierre Berthier who named it after the place where he found it, the village of Les Baux de Provence, in Arles, southern France.
In Spain we find bauxite, but in very small quantities in Teruel, Barcelona, Tarragona and Lleida.
In 1854 Bunsen managed to prepare aluminum electrolytically by starting from the compound sodium aluminum chloride in his experiments. That same year, Henri Sainte-Claire Deville perfected the process and manufactured aluminium for the first time in history, replacing potassium with sodium, and presented it at the Paris Exhibition of 1855, in the form of ingots. It can be said, therefore, that Deville was the initiator of the industrial production of the metal, whose process, with slight modifications, was used until 1888, when it was replaced by the electrolytic method.
The founders of the great aluminum industry were the Frenchman Hëroult, the German Kiliani and the American Hall, the former founding in 1888 of the company Aluminium Industrie Aktien Gesellschaft. About forty years after the foundation of the aluminium industry, in 1929, the first aluminium production plant of notable importance was founded in Spain located in Sabiñánigo (Huesca). The current production of primary aluminium in Spain is located in San Ciprian (Lugo), A Coruña and Avilés.
Aluminium is a metal too active to exist freely, being found in nature combined with a large number of minerals, the main ones being bauxite and cryolite. Bauxite is the most important of the aluminum minerals, it is a hydroxide whose composition does not correspond to a specific chemical formula because in all cases it is combined with variable amounts of the elements such as iron, silicon and titanium and an inconstant amount of combination water.
Its color varies from garnet to pure white. Cryolite is, with bauxite, the most important mineral in the manufacture of aluminium, its main role being that of alumina flux in electrolytic baths. Cryolite is currently being replaced by ciolite, an artificial fluoride of aluminum, sodium and calcium.
The extraction of aluminum from bauxite is carried out in three stages, mining, refining and reduction.
The bauxite is extracted, washed and dried before being sent to the refinery where it is separated from aluminium.
The Austrian chemist Karl Josef Bayer, son of the founder of the company Bayer Chemical, invented the Bayer process for the large-scale production of alumina from bauxite. This method is the most commonly used in the aluminum industry.
Starting from bauxite, previously subjected to a drying process and finely grinding the material, it is heated with a concentrated solution of caustic soda (NaOH) to obtain a solution of sodium aluminate (Al02Na) and some sodium silicate (Na2SiO2).
This solution is filtered and precipitated into aluminium hydroxide (Al(OH)3), either with carbon dioxide or with a small amount of previously precipitated aluminium hydroxide.
Alumina is reduced to aluminium in electrolyte cells of the Hall-Héroult procedure. In these cells, molten cryolite at 980ºC is used to dissolve alumina, which when subjected to electrolysis splits into aluminum and oxygen. The aluminum goes down to the bottom of the tank where it is periodically mined and the oxygen combines with the carbon in the anode to produce CO2.
By the action of the electric current supplied, the alumina introduced inside the cell or electrolytic furnace is decomposed and according to the laws that govern electrolysis, aluminum is deposited on the negative electrode (cathode) constituted by the lining of the furnace, from here the metal is extracted and cast in the form of rolling plates, billets or banknotes for extrusion or ingots for foundry.
According to the same laws, oxygen is produced at the positive electrode (anode), which, due to its high activity, reacts with the carbon of this electrode, forming the gaseous products mono and carbon dioxide (CO and CO2). Due to this reaction, the anode wears out, so it must be replaced periodically. The anode blocks are made of carbon.
To make 1000 kg of aluminium, 10,000 kg of bauxite is needed, which produces 500 kg of alumina, 80 kg of cryolite, 600 kg of coal plus 14,000 kWh of electrical energy. Due to their high electricity consumption, aluminum electrolysis plants are installed next to places where energy is cheaper, such as hydroelectric plants, nuclear or oil-producing countries.
One of the most remarkable characteristics of aluminium is its recyclability. Unlike other metals, 100% of the material can be reused. Likewise, this recycling process can be carried out almost indefinitely on the same material, so the useful life of aluminium can be considered practically unlimited.
Another of the most important conditioning factors of this recycling process is that it requires approximately 5% of the energy used to obtain primary aluminium.
On the other hand, the characteristics and properties of the material do not vary with this transformation, so the quality of primary and recycled aluminium is the same.
Aluminum is a very light silver metal. Its atomic mass is 26.9815, it has a melting point of 660ºC and a boiling point of 2,467ºC, and a density relative to 2.7 kg/m3. It is a very electropositive and extremely reactive metal.
On contact with air it is quickly covered with a hard, transparent layer of aluminum oxide that protects it from corrosion.
| PROPERTY NAME | VALUE OF ALUMINUM |
|---|---|
| Atomic No | .13 |
| Valencia | 3 |
| Electronegativity | 1.5 |
| Covalent radius (Å) Oxidation state | 0.50 (+3) |
| Atomic radius (Å) | 13 |
| Electronic configuration | [NE]3S23P1 |
| First ionization potential (eV) | 13 |
| Atomic mass (g/mol) | 13 |
| Density | 13 |
| Boiling Point (°C) | [NE]3S23P1 |
| Melting Point (°C) | 6.00 |
| Ionic radius | 26.9815 |
| Atomic Volume | 2.7 |
| Orbital filling | 2467 |
| No. of Electrons | 660 |
| No. of protons | 0.535 Å |
| Oxidation status | 10 CM3/MOL |
| 3P Valance Electrons | |
| Electrochemical equivalence | (NO CHARGE) 13 |
| Electron work function | 13 |
| Electronegativity (Pauling) | 3 |
| Fusion heat | 3 S2P1 |
| Valance electron potential | 0.33556G/AMP-HR |
| Elastic modulus: package | 4.28 EV |
| Elastic modulus: stiffness | 1.61 |
| Atomic mass (g/mol) | 10.79KJ/MOL |
| Elastic modulus Young | (-EV) 80.7 |
| Melting enthalpy | 76 GPA |
| Enthalpy of Atomization 26 | GPA |
| Enthalpy of vaporization | 70 GPA |
| Atomic volume | 322.2 KJ/MOL at 25ºC |
| Optical reflectivity | 10.67 KJ/MOL |
| No. of electrons | 293.7 KJ/MOL |
| Molar volume | 71% |
| Oxidation status | 9.99 CM3/TOPO |
| Specific heat | 0.9J/GK |
| Steam pressure | 2.4E-06PA AT 660.25°C |
| Electrical Conductivity | 0.377 106/CM |
| Thermal conductivity | 2.37 W/CMK |
