Download Extraction of Aluminum: Properties, Bauxite Ores, and Extraction Processes and more Slides Organic Chemistry in PDF only on Docsity! Ex.Lec.3 Extraction of Aluminum from ore oxide Dr. Ahmed Ameed 1 Introduction Aluminum has many useful properties. It is the commonest metal in the rocks of the Earth's crust. About 8% of the crust is aluminium, not the metal itself but combined with other elements as natural minerals, such as bauxite. MAIN PROPERTIES OF ALUMINIUM 1. An excellent conductor of heat and electricity. 2. Aluminium does not rust, it resists corrosion. 4. Low density compared with other common metals. 5. Good reflector of heat and light, it has a good metallic lustre (surface shine). 6. Nonmagnetic. 7. Can be alloyed to form stronger or harder alloys than pure aluminium. 8. Easily workable. It can be rolled into sheets, foil, and wire; cast or forged into useful shapes. Aluminium ores are Bauxite Al2O3.nH2O (Main) Gibbisite Al2O3.3H3O Diaspore Al2O3.H2O. It contains impurities as well as aluminium oxide. The bauxite must be purified to give alumina (Al2O3). Aluminium is a very reactive metal, much more reactive than copper, iron or lead. Other metals have been extracted for thousands of years by heating them with carbon (smelting). Carbon is also needed to extract aluminium, but in a completely different way. Ore dressing– cleaning ore by means of separation of the metal containing mineral from the waste (gangue). Ex.Lec.3 Extraction of Aluminum from ore oxide Dr. Ahmed Ameed 2 Bayer Process The bauxite ore is crushed and ground to produce slurry of coarse powder particles suspended in water. Sodium hydroxide (caustic soda) NaOH is added, and the slurry is heated with process steam to 160-180oC in a steel reactor or autoclave with pressure. The aluminum-containing hydroxides are dissolved during this digestion process, but other constituents of the bauxite remain solid. The digested bauxite suspension, which contains solids plus dissolved Al compounds, is referred to as pregnant liquor. It leaves the digester at about boiling temperature and passes through several stages of filtration referred to as clarification. Precipitation is conducted in large flat-bottomed tanks about 30 m high and 10- 12 m in diameter with typically 10 to 14 in a series. Cooled supersaturated liquor enters the first tank, and particles of aluminum hydroxide begin to precipitate. Seeds (small particles of aluminum hydroxide) are added to accelerate precipitation. Classification in which the aluminum hydroxide particles are separated from the liquor by a combination of cyclones and hydroclassifiers. The coarser particles proceed to the calciner. The finer particles are recycled as seeds. Calcination is the final step of the Bayer process. The particles are dried and heated to 1100C in either a rotary kiln (a tubular-shaped furnace that rotates as the powder passes through) or a fluidized bed (the kiln is stationary, but the powder is mixed by air bubbled through the powder bed). The aluminum hydroxide Al(OH)3 (is decomposed to form aluminum oxide (Al2O3) particles suitable for the Hall-Heroult electrolytic smelting process.
