The aluminium manufacturing process goes through two stages; the Bayer process and the Hall-Heroult process. To complete the process, the aluminium would go through 9 stages. Here they are:
The Bayer Process
- The bauxite ore has to be crushed as the first stage. The crushed ore will then be mixed with caustic soda and will be sent to a grinding tool. This will result to getting water suspension or slurry that contains fine ore particles.
- The slurry will be pumped to a digester and will be heated at 230-520°F (110-270°C) with pressure of 50 lb/in2 (340 kPa) for half an hour to several hours depending on the need and design of the intended product.
- The hot slurry is processed and turns into sodium aluminate solution. After which, it passes through different flash tanks.
- The processed slurry is pumped into a settling tank to separate the product from impurities called red mud.
- After the impurities are removed, the remaining liquid is pumped through cloth filters. The remaining impurities will be collected from these filters at this aluminium manufacturing process. The collected materials will be washed to gather remaining alumina and caustic soda that can be reused.
- The purified liquid is transferred into a set of precipitation tanks which is as tall as a 6-storey building. Every tank is added with alumina hydrate seed crystals. The seed crystals added increase in amount as they settle in the liquid and alumina.
- In this stage, the crystals precipitate and settle at the bottom of the tank. They are collected, washed and transferred to a kiln for them to be calcined or heated. A conveyor transfers the crystals into a cylindrical kiln. Water molecules are removed with 2,000° F (1,100° C) temperature which leaves off anhydrous or waterless alumina crystals which will then pass through a cooler.
The Hall-Heroult Process
- The alumina crystals are melted in a molten cryolite at 1,760-1,780° F (960-970° C) temperature to create an electrolyte solution.
- The last aluminium manufacturing process involves moving the crucible into a potline to gather molten aluminium and transfer it into a holding kiln and cast for it to be moulded.