Aluminium smelting is an industrial process used to extract the metal aluminium from aluminium oxide, or alumina. This relies on a chemical reaction catalyzed by exposure to electricity. Prior to the development of an effective aluminium smelting method, this metal was extremely difficult to obtain and was consequentially very expensive. This changed with the development of the Hall-Heroult Process, named for the two people who independently invented it, making the metal both cost-effective and readily available.
The first step in this process involves processing raw ore to produce purified aluminium oxide. This can include washing, grinding, and treating with caustic materials to leave behind a uniform white powder that will be ready for smelting. Treated alumina is mixed with cryolite and subjected to high temperatures to create a liquid mixture that passes into a vat. In the vat, electricity moves through the mix, causing molten aluminium to precipitate out to the bottom.
At an aluminium smelting facility, the vats are periodically drained using taps at the bottom to remove the metal. This process requires a number of controls, including a constant supply of electricity for continuous production because the contents of the vats cannot be allowed to solidify. If they do, a vat may require costly repairs, if it can be repaired at all. The high energy demands of aluminium smelting leads many facilities to position themselves near power plants for added security.
Numerous byproducts are generated during the aluminium smelting process. These include gases as well as mineral impurities that arise in the preparation of ore and the smelting itself. Pollution controls are an important concern for many companies that want to avoid damaging the environment and incurring heavy fines. Air filtration may be used to limit the release of toxins into the environment and waste products are processed carefully so they can be properly disposed of. Some byproducts can be used in the production of other goods, an appealing option when it is available.
Some confusion can arise between smelting and melting, because the two terms look similar. In smelting, a key chemical change occurs to the materials being processed; in this case, aluminium separates from the raw ore. It is a process used for extraction to remove useful metals from ore, rather than to process metals already in pure or alloy form, as is the case with melting. Once smelting is complete and metal is purified, melting can be included in future processing to make various components or prepare the metal for shipment.