The aluminium manufacturing process comes in two phases; the Bayer process and the Hall-Heroult process. The entire process is accomplished in 9 steps. Here they are:
The Bayer Process
- The first step is the crushing of the bauxite ore. After that, mix the ore with caustic soda and process it in a grinding to. The result would be water suspension or slurry which contains fine ore particles.
- The slurry is then pumped into a digester and heated to 230-520°F (110-270°C) under pressure of 50 lb/in2 (340 kPa) for half an hour to several hours.
- The hot slurry becomes sodium aluminate solution and is passed through a serious of flash tanks.
- The heated slurry is pumped into a settling tank. The phase allows the slurry to rest and for its impurities to settle. The residue that settled at the bottom of the tank is called red mud. It is a mixture of fine sand, oxides of trace elements like titanium and iron oxide.
- When the impurities are removed, the remaining liquid is pumped through sets of cloth filters. Any impurities are trapped and removed through the filters during this aluminium manufacturing process. The collected materials are washed to obtain alumina and caustic soda that can possibly be reused.
- The purified liquid is pumped into a set of six-story tall precipitation tanks. Alumina hydrate seed crystals are added in every tank. The seed crystals increase as they settle in the liquid and dissolve the alumina.
- In the process, the crystals precipitate and settle at the bottom of the tank. They are removed, washed and transferred to a kiln for calcining or heating. A conveyor moves the crystals into cylindrical kiln. Water molecules are driven off by 2,000° F (1,100° C) temperature leaving anhydrous or waterless alumina crystals. After that, the crystals are passed through a cooler.
The Hall-Heroult Process
- Alumina crystals are melted in a molten cryolite at 1,760-1,780° F (960-970° C) temperature to form an electrolyte solution.
- The last aluminium manufacturing process is the moving of crucible into a potline to collect molten aluminium and transfer it into a holding furnace and cast for moulding.