The Unsorted BBS Collection/thegreatunsorted.tar/thegreatunsorted/texts/term_papers/aluminum.esy

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                          EXTRACTION OF ALUMINUM


INTRODUCTION:
     An industrial process for extracting metals from their ores at
high temperatures.  Generally the ore is reduced with carbon or
carbon monoxide.  A flux is also used to combine with impurities
and form a slag on top of the molten metal.

DEFINITION:
     It is soft moderately reactive metal.  It is the second
element in group III.  It is the most common metallic element in
the earth's crust.  There are numerous minerals of aluminum.
Commercially important minerals are bauxite(Al2O3 * H2O),
corundum(anhydrous Al2O3), cryolite(Na3AlF6) and clays
mica(aluminosilicates).

DISCOVERY OF A WAY TO EXTRACT ALUMINUM:
     Hans Christian Oerstel, a Danish chemist, was the first one to
isolate aluminum in 1825 using a chemical process involving
potassium amalgam.  Between 1827 and 1845 Friedrich Wohler, a
German chemist improved Oerstel's process by using metallic
potassium.  He also was the first one to measure the specific
gravity of aluminum and show its lightness.  In 1854 Henri Sainte
Claire Deville(1818-81), in France obtained the metal by reducing
aluminum chloride with sodium.  Deville established a large-scale
experimental plant and displayed aluminum at Paris exposition of
1855.  In 1886 Charles Martin Hall in U.S and Paul L.T. Heroult in
France discovered that aluminum oxide would dissolve in fused
cryolite and could be then decomposed by electrolysis into a crude
molten metal.  This method is the best commercial method up till
now for the production of aluminum.
     The existence of aluminum was predicted in 1808 by the English
scientist Sir Humphry Davy, but he was unable to discover how the
metal is extracted from it.

OCCURRENCE AND EXTRACTION:
     Aluminum makes up between 7% and 8% of aluminum of the earth's
crust.  Aluminum is never found as free metal.  It is usually found
in the form of aluminum silicate or as a silicate of aluminum mixed
with other metals such as sodium, potassium, iron, calcium, and
magnesium.  These silicates are not useful ores because an
expensive process is required to extract aluminum from them.
Bauxite, an impure hydrated aluminum oxide is the commercial source
of aluminum.
     Most of the aluminum comes from a mineral called bauxite.
Bauxite contains aluminum oxide and often called Alumina.  The
alumina is obtained from the bauxite by washing and refining.
     In 1886, a process known as electrolysis was used in
separating chemical elements by passing an electric current through
a solution.  This process is based on the idea that certain
compound ionize when dissolved in a certain kind of liquids.  An
ordinary atom has equal number of electrons and equal number of
protons.  When a compound dissolves some of its atoms gain or lose
electrons.  Therefore the atom becomes unbalanced and the atom is
now called an ion.  If electrons are gained the atom becomes a
negative ion and if electrons are lost the atom becomes positive
ion.  This condition can occur when a substance is dissolved in a
liquid, such as when alumina which is composed of two atoms of
aluminum and three atoms of oxygen.  When it is dissolved in liquid
called cryolite a part of the Al2O3 breaks into atoms of aluminum
and atoms of oxygen.

     2Al2O3 -------------------- 4Al + 3O2

     The oxygen atoms gain extra electrons and the aluminum lose
some of their electrons.  The cryolite solution now contains Al2O3
dissolved in a large amount; a small number of positively charged
by aluminum atoms and a small number of negatively charged oxygen
atoms.  Electrolysis is then used to separate chemicals.  Two
sticks of carbon called electrodes are put into a chemical
conducting solution and a current passed between them, so that one
electrode has a positive charge and the other negative charge.  The
positive aluminum ions move towards the negative and the negative
oxygen ions move toward the positive.
     Aluminum industry requires two important things.  The 1st is
the electricity and the 2nd is aluminum ore called bauxite.  A
powerful electric current is passed through the mixture in an
electrolytic cell.  The current generates a temperature of about
1,000  C(1,832  F).  The aluminum melts and falls to the bottom of
the cell, where it is collected.  This process needs large amounts
of electricity.  About 10 kilowatts-hours of electricity are needed
to make 0.5 kg(1 lb) of aluminum.  Because of this most aluminum is
extracted in areas where hydroelectric power is plentiful.

PROPERTIES AND USES:
     Aluminum is strongly reactive metal.  When aluminum is in
contact with air, aluminum quickly becomes covered with a
transparent layer of oxide that resists further corrosive action.
Because of this, materials made of aluminum never rust.  Aluminum
also helps to reduce many other metallic compounds to their base
metal.  Example:  When thermite, a mixture of powdered aluminum and
iron oxide is heated the aluminum moves the oxygen quickly from the
iron.  Aluminum melts at 660  C(1120  F) and boils at 2327  C(4221
F).  Aluminum stands up well against most acids but it is attracted
by strong solutions of alkalies such as ammonia.  Because aluminum
has a high melting point it is used as a furnace lining and for
refractory brick.  Aluminum is also ductile and so it is suitable
for drawing into wire.  It is also malleable and this makes it easy
to roll into sheets and foil.  Aluminum has a strong affinity for
oxygen and never is found in the bold purely metallic condition.
The oxide layer can be thickened by anodizing.  Anodizing is
oxidation by an electrolysis process.  The anodizing layer can be
dyed and so it becomes useful for architectural panels and
household utensils.  The physical properties of aluminum determines
some of the uses for it.  Because aluminum has a high electrical
conductivity, moderate cost and weights less than almost all metals
except for lithium, beryllium and magnesium, it is used as an
electrical conductor on long distance power lines.  Aluminum is
used to transmit electricity at 700,000 volts or more.  Aluminum's
good heat conductivity and low density make it an ideal material
for making pots, pans, and pistons of internal-combustion engines.
Because aluminum is malleable and ductile inexpensive and has a low
density, aluminum alloys are used as structural materials in
trains, recyclable food containers and work of art.  Aluminum is
also used as a material in low-temperature nuclear-reactions
because it absorbs relatively few neutrons.  Aluminum becomes
stronger and toughs as it gets cold and it is therefore used at
cryogenic temperatures.  Aluminum could be pressed into a foil
which can wrap food, candy and cigarettes.  Aluminum foil of 0.018
cm could be used to protect food spoilage.  Because of its light
weight it is widely used for making containers, flexible packages
and easy to open bottles and cans.  Aluminum's resistance to
corrosion in salt water also makes it use ful in boat hulls and
various aquatic devices.  Because aluminum has a shiny surface it
is used in coating asbestos fire fighting gear and space units
because it reflects light and heat and keeps the people who wear
them cool.  Aluminum is used in jewellery for its ability to be
polished and dyed.
     Powdered aluminum is used for aluminum paint.  In powder form
it is considered more reactive than in solid state.  That makes it
useful as strong reducing agent for removing oxygen in chemical
process.

USES OF ALUMINUM COMPOUNDS:
     Crystalline alumina is used as an abrasive, and in powder form
for column chromatography.  Chromatography is an analysis technique
in which a liquid mixture of compounds is allowed to go down
through a column containing alumina powder.  This causes the
various compounds to separate at different levels.  Aluminum
hydroxide Al(OH)2 is used as a moderant in dying.  Aluminum
hydroxide dissolves in acids to form salts and in alkalis it forms
aluminates.  Sodium aluminate is used as a flocculating agent to
purify water and sewage by coagulating around impurities.  It is
used in paper making aluminum hydroxide.

MAKING ALUMINUM HARDER:
     Although aluminum is naturally light and flexible, it is not
strong.  There are two ways in which the strength of aluminum could
be increased.  One is by cold-working: hammering or rolling the
metal at a room temperature.  This compresses the metal and makes
it harder.  The other method is alloying.  The metals most
frequently alloyed with aluminum are copper, magnesium, manganese,
nickel, iron, zinc, and silicon.
     Aluminum on its own is soft, it also owes extraordinary
versatility to the properties it acquires when different elements
are mixed together.
Examples:
-copper makes it stronger.
-boron increases its ability to conduct electricity.
-magnesium makes it corrosion-resistant so that it could be used in
 boat hulls and kitchen utensils.
     Duralumina is a strong and light alloy of aluminum.  It is
made of small portions of magnesium, copper and manganese.

RECYCLING ALUMINUM:
     Since lots of energy is needed to separate aluminum from the
ore so recycling would be a very useful method.  Aluminum is
recovered from cans and other scrap therefore aluminum refining
process is not necessary.  For this reason, aluminum is an energy
saver since recycling requires only 5 % of energy used to produce
the same amount of aluminum from the bauxite.  Aluminum is
considered to be the most recyclable of all metals.

WHERE IS BAUXITE FOUND?
     Bauxite have been discovered on every continent except
Antarctica, but the types contain the most alumina are found in the
tropical and sub-tropical parts of the world.  Australia has the
largest deposits.  The world's biggest bauxite mines, at Welpa in
Queensland contain 3,000 million tonnes of ore.  It produce about
25 % of world's supply.  Also Jamaica, Guinea, Guyana, and Brazil
have large deposits.

ALUMINUM COMPANIES:
     Production of most of the world's aluminum is controlled by
just a few companies.  The giant of them is Aluminum Company of
America which has more than fifty factories in different parts of
the world.  Alcan Aluminum Ltd, which is in Canada is also one of
the major companies.  It has factories all over the world for
refining alumina, production alumina and making aluminum products.

PRODUCING ALUMINA:
     When bauxite has been mined it is taken to an alumina plant.
The unwanted parts of the ore is removed to leave aluminum oxide.
Alumina is still produced by the method that first the crushed and
dried bauxite is mixed with caustic soda and pumped into steam
press ore tanks called "digesters".  The alumina in the bauxite
dissolves leaving a mass of impurities known as red mud.
     The red mud is removed by filtering the mixture under
pressure.  Alumina then is pumped into tanks for the red stage of
the process.  Small amounts of a chemical compound called alumina
trihydrate are added and the mixture is agitated for a day.  As the
mixture cools it causes the liquid alumina to separate into
crystals of pure alumina trihydrate and caustic soda.  The caustic
soda is removed and re-used.
     Alumina is now a damp, creamy substance.  It is ready for the
final stage which is calcination.  The alumina is washed to remove
any traces of caustic soda.  Then it is put into long rotary kilns
which are slowly heated to a temperature of 1,000  C.  This dries
out all the moisture from the alumina leaving a fine white powder.
The powdery alumina is then left to cool and stored in large silos.
then it is sent to aluminum plant.



DISADVANTAGES OF ALUMINUM:
     Aluminum has a chemical property which is somehow considered
harmful.  Aluminum reacts with both acidic and basic substances to
form soluble aluminum compounds.  Soluble to form soluble aluminum
compounds are harmful to health.  Aluminum foil wrap and cooking
pots made of aluminum reacts with tomato sauce, and dishes
containing vinegar or wine.  Because of this disadvantages good
quality aluminum pots and pans have their cooking surface coated
with inert layer of ceramic or teflon in order to keep the food
separate from aluminum metal surface.

SHAPING THE METAL:
     There are 2 main ways of shaping aluminum and aluminum alloys.
These are known as wrought form and cast forms.
     Wrought forms are made by shaping the solid slabs or billets.
Cast forms are made by pouring molten metal into moulds.  Wrought
are shaped by rolling.  Cast forms are not as strong as wrought
forms casting is carried out in a foundry.  Aluminum or aluminum
alloy are melted in a furnace and poured into a shaped mould where
the metal hardens and sets.
     There are 2 methods of casting. One is sand casting, where the
metal is poured into sand moulds.  The other is pressure die
casting, the molten metal is forced into metal moulds called dies
under pressure.  The dies are then cooled with water when they are
hard the casting are turned out of the moulds and cleaned.

BIOCHEMICAL AND ENVIRONMENTAL HAZARDS OF SMELTING:
     All smelting process produce large amounts of carbondioxide as
a waste product.  Carbondioxide is considered the main gas that is
responsible for the green house effect: the warning of the earth
through changes in the composition of the atmosphere by 20 %.
Biochemical and environmental hazards of aluminum oxide was by far
the most widely produced toxic waste among the biggest polluters.
Aluminum oxide is harmful to the respiratory system and linked to
brain damage.  Also white clads of aluminum oxide result by burning
aluminum powder billows from the solid booster rockets that lift
the shuttle.



JOBS CREATED:
     Many jobs are created after the discovery of aluminum.
Workers are needed to mine the aluminum.  Others are used in
factories to extract the aluminum from the ore.  Since aluminum is
used in manufacturing many different products, workers are needed
to help in the manufacture of these products.

ECONOMY:
     Mining aluminum ores helps the country to become more
prosperous by exporting some of these extracted ores and using the
rest in different types of manufactures.  This also will help the
country by creating more jobs which is another type of helping the
economics of our society since aluminum could be recycled, it is
considered an economizing metal since it uses less energy.

COULD SOCIETY DO WITHOUT IT:
     Since aluminum has many different uses and it a recyclable
metal then it is considered an important metal.  Because it is
recyclable it saves lots of energy.  It is also used in different
kinds of industries such as in aircraft bodies, windows frames,
housesidings, cooking utensils, pistons of external combustion
engines, trains and recyclable food containers.  There are lots of
others uses for aluminum that is why it is an important source.

FACTS ABOUT ALUMINUM:
     Chemical symbol = Al
     Atomic weight = 26.9815
     Specific gravity = 2.70(over 2 1/2 times as heavy as water).
     Colour = Silver white with a blush tonge.
     Properties = soft, easily shaped, resists corrosion, non-
manganese, good conductor of heat and electricity, forms
          compounds that are hard to break down.
     Occurrence = third most abundant element in the earth's
crust(after oxygen and silicon) most abundant metal in           the
earth's crust.
     Chief Ore = bauxite(named after town of Les Baw in southern
          France, where it was first mined).



















                              REFERENCE LIST

1.   Dr.  John R. Wilson.  The Rain tree Illustrated Science
Encyclopedia.  1984

2.   Dineen, Jacqueline.  Focus on Aluminum.  England, Wayland.
     1988.

3.   Daintith, John.  Facts on file Dictionary Chemistry.  New
     York.  1988.

4.   Steven G. Weinfeld.  Funk and Wagnalls New Encyclopedia.
     United States.  1876.

5.   Aluminum.  The New how it Works Science and Invention
Encyclopedia.  1987.

6.   Aluminum.  Science and Technology Illustrated.  1984.