Aluminum can be produced through primary or secondary smelting. Primary smelting involves extracting aluminum from bauxite ore, while secondary smelting involves extracting it from waste materials or by-products. Primary smelting is more complex and energy-intensive, while secondary smelting requires less energy but produces less pure aluminum.
Aluminum smelting is an industrial process used to produce metal. How this occurs depends on whether the aluminum is produced via a primary process, involving bauxite, or a secondary process, involving scrap. The primary process is the most complex and energy intensive.
Aluminum production is generally divided into two categories, primary and secondary. Primary smelting of aluminum involves a process that begins with the extraction of the metal from bauxite ore, a type of rock most commonly found in tropical and subtropical climates. This process begins by first obtaining a raw material known as alumina from bauxite.
To achieve this, the ore that has been sorted and ground is mixed with sodium hydroxide under conditions of high temperature and high pressure. This step is known as digestion and the machine used is often called a digester. The agitation and conditions within the digester result in the separation of sodium aluminate and bauxite residues. The residues tend to sink to the bottom of the dough. It is then necessary to separate the residues from the alumina, which is obtained by filtration.
When alumina is first filtered, it can be found in crystallized form. These crystals undergo a process known as precipitation, which involves the use of alumina hydrate to create a purer form of alumina crystals. The next step is calcination, which involves washing away the impurities and removing the water from the crystals. This part of the process requires the use of high levels of heat and will ultimately result in a white powder, which is alumina.
At this point, casting the aluminum will involve converting the powder into a metallic form. This requires large amounts of direct current (DC), which runs in a contraption called a reducing pot. The metal that is produced in the reduction vessel generally settles on the bottom and is periodically decanted. Merging is usually a non-stop process.
Secondary aluminum smelting is a little different because it involves extracting the metal from waste materials or by-products known as slag, which are created when primary aluminum is smelting. When salvage is merely from scrap, the material is usually smelted in a gas reverb, oil reverb or hearth furnace. Chemical solutions are then used to remove impurities and produce aluminum of varying purity. When it comes to slag, it must first be processed similar to bauxite ore before the metal can be extracted using the heat source.
Primary smelting of aluminum is generally an energy-intensive process. Secondary smelting requires only a fraction of the energy required for a primary process. The aluminum produced is usually not 100% pure. At best, it can be 99.7 percent pure.
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