Aluminum is a silver white metal, which ranks third in the earth's crust next to oxygen and silicon. The density of aluminum is small, so it is called as light metal.
Aluminum is a non-ferrous metal with high yield and high usage. It is second only to steel in the world. The density of aluminum is about 1/3 of the density of steel and copper.
Bauxite ore is the primary raw material source for aluminum production. This ore consists primarily of the minerals gibbsite Al(OH)3, boehmite, and diaspore AlOOH, together with minor fractions of iron oxides, clay minerals, and small amount of TiO2. The bauxite ore must first be refined into alumina (aluminum oxide) before it can be electrolyzed into aluminum ingot. According to a recent survey by the International Aluminium Institute (IAI), the production of one metric ton of alumina requires approximately 2.9 metric tons of bauxite (taking into account the purity of bauxite and losses during processing and transportation) (IAI 2013). Raw materials for alumina production include bauxite, caustic soda, and sodium carbonate.
Alumina: Alumina (Al₂O₃) is a high hardness compound with a melting point of 2054℃ and a boiling point of 2980℃. It is an ionized ionic crystal at high temperature. It is often used in the manufacture of refractory materials. Industrial Al₂O₃ is made of bauxite and diaspore. For high purity Al₂O₃, it is usually prepared by chemical method.
Al₂O₃ has a lot of homogenous crystals. There are more than 10 known kinds of crystals. There are mainly 3 crystal types, namely, γ-Al₂O₃、β-Al₂O₃、α-Al₂O₃. The structure is different in nature and almost completely converted to α-Al₂O₃ at high temperatures above 1300℃.
In addition to the alumina, carbon anodes are used in the electrolysis process to produce primary aluminum ingot. Anodes are made from petroleum coke and coal pitch, and are consumed in the process of separating the alumina into aluminum and oxygen gas. The final composition of the aluminum ingot varies by alloy, but is typcially greater than 90% aluminum by mass.
The manufacturing of primary aluminum ingot includes the component processes of bauxite mining, alumina refining, electrolysis (including anode production and smelting), and primary ingot casting. The intial raw material is bauxite ore and the final product is primary aluminum ingot with intermediate products of alumina (aluminum oxide) and molten aluminum (liquid) metal. Primary aluminum is a liquid aluminum that is produced in the process of electrolysis, without precipitation and so on. The primary aluminum can be made into aluminum ingot by cooling into the cast aluminum ingot model. Therefore, alumina is the primary material of aluminum liquid, the electrolytic aluminum is the process, the primary aluminum is the aluminum liquid in the electrolysis process, the aluminum ingot is a kind of aluminum product, and finally it is sold on the market.
There are two generic types of electrolysis technologies for aluminum: Prebake and Söderberg. The two technologies differ in the type of anodes they consume. As a consequence of advanced design and better computer control of the Prebake technology, the efficiency and emission levels have been significantly improved. Approximately 95% of the production in North America in 2010 was from Prebake technology and 5% was from Söderberg technology.
Aluminum ingots can be divided into high purity aluminum ingots, aluminum alloy ingots and remelting aluminium ingots according to their composition, and can also be divided into round ingots, plate ingots, strip ingots and T-shaped ingots according to their shape and size.
Molten metal from electrolysis is siphoned from the pots and sent to a resident cast house for further alloying, heat treatment, fluxing, and filtering as necessary for the final product. The metal is then cast into ingots in a variety of methods: open molds (typically for remelt ingot), through direct chill molds for various fabrication shapes, electromagnetic molds for some sheet ingots, and through continuous casters for aluminum coils. Aluminum products are often made from both primary and recycled ingots • There is no relevant chemical composition difference between primary and secondary ingots if both are governed by the same alloy designation and chemical composition limit standards • The service life of the final product depends on its application, but is typically long due to aluminum’s excellent corrosion resistance • For that same reason, maintenance needs during use are usually low.
