1. Aluminum

2. Assessment statement Describe and explain the production of aluminum by electrolysis of alumina in molten cyrolite. (Include the use of cyrolite as a solvent because of the very high melting point of Al2O3 and the type of materials used for the construction of the cell and choice of electrodes.)

3. Production of Aluminum Aluminum is primarily made by the electro lytic reduction of aluminum oxide. Aluminum oxide or aluminum does not occ ur naturally. The main ore of aluminum is bauxite. Bauxite is in the form of mainly aluminum hydroxide Al(OH)3, and other impurities su ch as iron(III) oxide and titanium hydroxide, and other few oxides.

4. Bayer process Bayer process is the process of extracting aluminum oxide from bauxite. Bauxite is powdered prior to the process. As aluminum oxide is amphoteric, it dissol ves in sodium hydroxide solution. Al(OH)3(s) + NaOH(aq)  NaAlO2(aq) + 2H2O(l)

5. The aluminate solution is filtered leaving b ehind the impurities. Seeding with aluminum hydroxide then re verses the reaction. The pure recrystallized aluminum hydroxid e is then heated to produce aluminum oxid e (alumina). 2Al(OH)3  Al2O3(s) + 3H2O(l)

6. Use of cryolite To make the electrolysis happen, alumina has to be in aqueous state. Alumina has a very high melting point of 2045°C. Cryolite (sodium hexafluoroaluminate(III), Na3Al F6) melts at about 950°C and the solution can di ssolve alumina sufficiently well. Considerable energy is still required to heat cryo lite and dissolve alumina, but it is much more en ergy-efficient than melting the alumina itself.

7. Natural cryolite is depleted long ago, thus synthetic cryolite is needed. The aluminate solution (NaAlO2(aq)) from Bayer process is used in separate process to make synthetic cryolite. Hydrogen fluoride and sodium carbonate i s added to the solution to precipitate cyrolit e. NaAlO2(aq) + 6HF(g) + Na2CO3(aq)  N a3AlF6(s) +3H2O(l) + CO2(g)

8. Hall-Heroult process Hall-Heroult process is an electrolysis proc ess that extracts aluminum out of alumina (aluminum oxide). Overall cell reaction is Alumina + carbon = aluminum + carbon di oxide

10. Assessment statement Describe the main properties and uses of aluminum and its alloys.

11. Properties of aluminum Malleable and can be shaped easily Excellent conductor of heat and electricity Has much a lower density than iron, yet can for m alloys that are stronger than steel Resistant to corrosion due to its protective layer of aluminum oxide The thickness of the oxide layer can be further in creased by a process known as anodizing.

12. Uses of aluminum UseExamples TransportSuperstructures of trains, ships and airplanes. Alloy engines for cars. ConstructionWindow frames, doors roofing Power transmissionOverhead electricity cables, capacitor foil Kitchen utensilsKettles, saucepans PackagingDrink cans, foil wrapping Chemical industryAl(OH)3 – flame retarder, paper making Al2(SO4)3 – flocculant in sweage treatment and to precipitate PO43- Al2O3 – catalyst and catalytic support material, abrasive

13. Assessment statement Discuss the environmental impact of iron a nd aluminum production.

14. Environmental impact Smelting processes of aluminum requires enorm ous amount of electricity. Also, the main process which is the electrolysis emits carbon dioxide which is greenhouse gas. Recycling aluminum is an important method of s aving energy and minimizing the environmental damage. Recycling aluminum requires only 5% of the ene rgy to produce the same amount of aluminum fro m bauxite.