Cairo University Faculty of Engineering 2nd year Dept of Metallurgy

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Extraction of Aluminum Prepared for : Dr/ Randa Abd El-karim

1.Gaber Alaa El Din gaber B.N 20 2.Ahmed Hatem Omar B.N 3 3. Tarek Emad El-Din B.N 26 4.Mohamed Ibrahim Hanafy B.N 31 5.Bishoy Shawky Alfy B.N 19 6.Kareem Mohamed B.N 29 Prepared by :

General Principles Metals are found in the Earths crust. The least reactive metals are found as elements (i.e. native, e.g. silver, gold), but most metals are found in compounds, usually oxides or sulphides, Ex: Al, Fe. Aluminum and iron are very widely distributed in the Earths crust, and so they are used in many applications.

Methods of Extraction There are a number of different methods of metal extraction, including: by heating with carbon (in the form of coke) (e.g. Fe, Cu) by heating with a more reactive metal (e.g. Ti) by electrolysis of melts (e.g. Al) by reduction with hydrogen gas (e.g. W)

Methods of Extraction Which method is used depends on: 1) the energy requirements: fuel, electric sources,….. 2) the cost of the reducing agent: carbon (in the form Of coke) is cheap, but some reducing agents (more reactive metals) are expensive 3) the metal purity required: the higher the required purity, the greater the cost in obtaining that purity 4)position of the metal in the reactivity series

Reactivity Series the reactivity series or activity series is an empirical series of metals, in order of "reactivity" from highest to lowest K Na Ca Mg Al C Zn Fe Sn Pb H Cu Ag Hg Au Pt

K Na Ca Mg AlZn Fe Sn PbCu Ag Hg Au Pt Electrolysis Reduction with carbon Occur native or electro refined Reactivity Series

Extraction of Aluminum Aluminum is at the top of the reactivity series Then it is highly reactive Then the bonds in its compound are very strong So Aluminum is extracted by electrolysis The raw materials for the extraction of aluminum are purified aluminum oxide (Al 2 O 3 ) and cryolite (Na 3 AlF 6 )

The most important ore of aluminum is a rock called “Bauxite” Bauxite consists of minerals Aluminum oxide Al 2 O 3 Gibbsite Al(OH) 3, Diaspore α-AlO(OH), Hematite Fe 2 O 3, and Quartz SiO 2 95% of the world's bauxite production is processed first into Aluminum oxide “Alumina” Al 2 O 3

Alumina is then processed into Aluminum by electrolysis Bauxite is converted to Alumina through a process called “Bayer process” In the Bayer process bauxite is washed with a hot solution of Sodium hydroxide NaOH This converts Alumina to Aluminum hydroxide Al(OH) 3

Aluminum hydroxide dissolves in the solution Other components of bauxite do not dissolve These solid impurities are filtered off

Extraction of Aluminum The hydroxide solution is cooled and Aluminum hydroxide precipitates Aluminum hydroxide is then strongly heated to 1050 c (calcined) giving off water vapor and Aluminum oxide is produced 2Al(OH) 3  Al 2 O 3 + 3H 2 O Bayer process electrolysis

Extraction of Aluminum In electrolysis the aluminum oxide must be molten or dissolved to conduct electricity, and so is dissolved in molten cryolite (this requires a lower temperature than using molten aluminum oxide alone so has lower energy costs) The electrodes are made of graphite Note: Cryolite is added to aluminum oxide to lower melting point and to dissolve Al2O3, so energy is saved

carbon-lined steel vessel acts as cathode CO 2 bubbles Al (l) Al 2 O 3 (l) Draw off Al (l) - + from power source Al +3 O -2 Al +3 O -2 graphite anodes  e- e- e- e- 

Overall cell reaction: 4 Al O C(s)  4Al(l) + 3CO2(g) Anode reaction: 2O 2- (l) +C(s)  CO2(g) + 4e - X3 Cathode reaction: Al 3+ (l) + 3e -  Al (l) X4

Extraction of Aluminum Al 3+ gains 3 electrons from the cathode to form molten aluminum, which is tapped off O 2- loses 2 electrons to the anode to form oxygen 2O 2- (l)  O 2 (g) + 4e - Oxygen released attacks carbon anode, to form Carbon monoxide/dioxide Note: Carbon anode burns due to the oxygen produced forming CO 2 so the carbon anode needs to be replaced regularly

Applications on Aluminum PropertiesApplications Low density, light, resistant to corrosion, Good electrical conductivity Electric cables Non toxic, resistant to corrosion, good heat conductivity Food containers Low density, light, high tensile strength, resistant to corrosion Aircraft body

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