cairo university faculty of engineering 2nd year dept of metallurgy
TRANSCRIPT
Cairo University
Faculty of Engineering
2nd year
Dept of Metallurgy
Cairo University
Faculty of Engineering
2nd year
Dept of Metallurgy
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