Cairo University

Faculty of Engineering

2nd year

Dept of Metallurgy

Cairo University

Faculty of Engineering

2nd year

Dept of Metallurgy

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2

Extraction of Aluminum

Prepared for :Dr/ Randa Abd El-karim

Extraction of Aluminum

Prepared for :Dr/ Randa Abd El-karim

1.Gaber Alaa El Din gaber B.N 202.Ahmed Hatem Omar B.N 33. Tarek Emad El-Din B.N 26 4.Mohamed Ibrahim Hanafy B.N 315.Bishoy Shawky Alfy B.N 196.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 Al Zn Fe Sn Pb Cu Ag Hg Au Pt

ElectrolysisReduction with

carbonOccur native orelectro 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 (Al2O3) and cryolite (Na3AlF6)

The most important ore of aluminum is a rock called “Bauxite”

Bauxite consists of minerals Aluminum oxide Al2O3 Gibbsite Al(OH)3 , Diaspore α-AlO(OH) , Hematite Fe2O3 , and Quartz SiO2

95% of the world's bauxite production is processed first into Aluminum oxide “Alumina” Al2O3

• 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 Al2O3 + 3H2O

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 vesselacts as cathode

CO2 bubbles

Al (l)Al2O3 (l)

Drawoff Al (l)

-

+frompowersource

Al+3

O-2

O-2

Al+3

O-2

graphite anodes

e-

e-

• Overall cell reaction: 4 Al3+ + 6O2- + 3C(s) 4Al(l) + 3CO2(g)

• Anode reaction: 2O2-(l) +C(s) CO2(g) + 4e- X3

• Cathode reaction: Al3+(l) + 3e- Al (l) X4

Extraction of AluminumAl3+ gains 3 electrons from the cathode to form molten aluminum, which is tapped off

O2- loses 2 electrons to the anode to form oxygen

2O2-(l) O2(g) + 4e-

Oxygen released attacks carbon anode, to form Carbon monoxide/dioxide

Note: Carbon anode burns due to the oxygen produced forming CO2 so the carbon anode needs to be replaced regularly

Applications on Aluminum

Properties Applications

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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