CLICK HERE FOR INDEX PAGE
 
ALUMINIUM PRODUCTION

V.Ryan © 2019

 
PDF FILE - CLICK HERE FOR PRINTABLE WORKSHEET
 

BAUXITE TO ALUMINIUM

 
Aluminium is derived from bauxite, a sedimentary rock, distributed widely throughout the world. One such source is Australia, where open cast mining allows easy access to the bauxite ore. An electrolytic reduction process is used to extract the valuable aluminium oxide, from the ore. However, this requires large amounts of electricity and consequently, aluminium production is usually associated with a source of cheap hydroelectricity.  
 
 
 
1. GRINDING / CRUSHING:
Bauxite ore is crushed in a high temperature, rotating grinding mill, where it is mixed with sodium hydroxide. This produces a slurry (thick liquid) of sodium aluminate and small amounts of other metals.
 
2. SLURRY TANK:
The ‘other metals’ are heavier than the sodium aluminate and sink to the bottom of the slurry tank, where they are removed.
 
 
  3. THE DIGESTER
Chemical reactions take place in this tank, further dissolving the alumina. The solution is heated for a number of hours, to enable the chemical reaction, with more sodium hydroxide being added periodically.
 
 
 
  4. SETTLING:
The solution is allowed to settle, which leaves more of the heavier unwanted metals, at the bottom of the settling tank and the alumina solution at the top. This is ‘pumped’ to the next stage of the process.
  5. PRECIPITATION TANKS:
The alumina solution is stored in a series of precipitation tanks. Crystals of alumina are added and these start to grow, as the alumina cools and forms into larger crystals, around the original crystals. As they gain in weight, they begin to settle at the bottom of the precipitation tank and are finally removed.
     
6. CALCIFICATION:
The alumina crystals are heated to remove water. The central screw moves the crystals to the end of the heated calcification tank. With the water removed, the result is a white powder of pure alumina (aluminium oxide).
 
 
 
 
7. SMELTING IN A FURNACE:
The pure alumina is dissolved in a molten solution of ‘fused’ cryolite (sodium and aluminium) and fluorspar (calcium fluoride). An electric current keeps the mixture molten, at a temperature of 900 degrees centigrade. Aluminium forms at the bottom of the furnace and can be poured into a cradle. The impurities combine with the carbon anode to form carbon dioxide, escaping at the top.
 
 
 
 
CLICK HERE FOR RESISTANT MATERISALS INDEX PAGE
 
Google
 
Web www.technologystudent.com