Aluminium

I. INTRODUCTION

1.1 Background
Aluminum is an element with the symbol Al, numbered
atoms 13 and an element of group III A. Physically aluminum
is a silvery white metal with a character like the metal on
Generally, aluminum metal to reflect light, non-toxic,
non-magnetic and not shiny. Aluminimum is one
from 8 major element in the earth's crust, is an element of the 3rd
most abundant in nature that is about 8.1% weight.
Aluminium is not found in nature in the form of metal
pure but in the form of bauxite which still contain
Fe2O3, and Si2O3. That required further processing to
obtain pure aluminum commonly used and sold
commercially
Aluminum is a good electrical conductor, heat resistant
and corrosion resistant. Aluminum is used in many ways.
Most are used as high-voltage cable, material
aircraft construction and household appliances such as pots, bottles
soft drinks and milk bottle caps. Aluminum is usually also
used to coat the lights and compact disks. Compound
Aluminium also has a very broad application. For example
Aluminium sulphate is used for water purification.
1.2 Problem Formulation
The problem that we adopted in this paper
among others:
1. How Aluminum element abundance in nature?
2. How does the whole process being undertaken to
obtain aluminum from bauxite?
3. How to use an aluminum element in life? 3

II. DISCUSSION
2.1 Aluminium in Natural Abundance
Aluminum is one of the abundant element in nature
especially on the earth's crust, which is about 8.1% weight. Although
abundant, but the aluminum metal is never
found in the pure metal in nature. Rather joined
elements - other elements to form a mineral. For example compounds
with a group of silicate which is usually called feldspar, which is
The most abundant mineral in the earth's crust. One type
aluminum silicate mineral that is piropilit AlSi2O5 (OH), addition,
usually combined with manganese to form a mineral called
spesartin, Mn3Al2 (SiO4) 3. Aluminum silicate containing Floride
or hydroxide, Al2SiO4 (F, OH) 2, forming a mineral gem
called topaz, aluminum silicate with potassium named
mikrolin, KAlSi3O8, which is usually green apples until
brown (Navy, 2009).
Aluminum oxide, Al2O3, called alumina and there in the wild
as the mineral corundum. Korumdum containing impurities
Emery called, which is used as a scourer bisasanya
and wheels. Pure corundum is colorless, but with the
some impurities will make the colored korumdum.
For example, with chromium oxide impurities will produce a color
called Ruby red stone, with titanium oxide will be obtained
sapphires are usually colored blue. Aluminum and magnesium
would produce spinel oxide minerals, join the phosphate will
produce mineral varisit, AlPO4.2H2O, which produces color
green and very popular as ornamental stone manufacture
(Navy, 2009).
Aluminum oxide compound of the most common are bauxite, or
pure aluminum containing aluminum oxide in jumlah4
large. Usually a combination of aluminum and oxygen
with formula Al2O3.2H2O. in bauxite is also found several
impurities such as Fe2O3 and SiO2. Therefore, to obtain
pure aluminum metal required more processing bauxite
information. (Davydson, 2009).
Bauxite reserves are scattered throughout the world. State - State
have a source of bauxite in large numbers include: Australia,
Brazil, Guinea, and Jamaica. About 85% of the total bauxite
mined from the earth's crust, is used to produce metal
aluminum, which will be used as raw material products
- Other products are more varied. The remaining approximately 15% used
for sustainable chemical processes at the factory - the factory in
pembutan pesenyawaan aluminum dengn particular purpose (Davydson,
2009).
Map of the World Bauxite Mine
http://www.hs.wisd.org/ddaughenbau
gh/Picture5
2.2 Process Isolation of Aluminum from Bauxite
In general, to obtain pure aluminum from bauxite
done in 2 stages of the process, namely Bayer process and Hall-Heroult process.
In the Bayer process, bauxite is purified to obtain aluminum
oxide. The next process, process-Heroult Hall, melt aluminum
dioxide to obtain pure aluminum metal (Anonymous, 2007).
The Bayer process
In general, the Bayer process consists of 3 stages. Namely: extraction,
Precipitation and Calcination (Anonymous, 2009). In the process of extraction,
bauxite is mechanically crushed and then dissolved in
hot sodium hydroxide solution at 175 milk
o
C, this will pelarutsn
dissolve the aluminum oxide to aluminum hydroxide, Al (OH) 3.
With OH
-
excess will produce [Al (OH) 4]
í
.
Al2O3 + 2 OH
í
+ 3 H2O L 2 [Al (OH) 4]
í
Other components in addition to aluminum oxide (impurities) are not soluble.
So that the aluminum oxide from bauxite will be separated from
pengotornya like Fe2. Separation can be done by filtering
to the insoluble solid impurities, called Red Mud. After
separated by an insoluble pengotornya, get in on the process
precipitation. Filtrate solution containing the aluminum hydroxide is cooled,
so that the resulting dense white precipitate shaped like a thread -
yarn. The next stage of calcination, where the solid white
aluminum hydroxide is heated to a temperature of 1050 ±
o
C, at proses6
This heating aluminum hydroxide will decompose
into alumina, and produces water vapor in the process
(Anonymous, 2009):
2 Al (OH) 3 L Al2O3 + 3 H2O
Bayer Prose By Gradual:
· Bauxite is mechanically crushed, then mixed
with caustic soda (NaOH), the resulting aqueous suspension
contain a wide variety of pure particles.
· Suspense liquid is pumped into the digester (which serves Tank
such as pressure control tube). Solution
heated to a temperature of 230-520 ° F (110-270 ° C) under
pressure of 50 lb / in
2
(340 kPa). In this condition, done
for about half an hour or up to several hours. In
the process is carried out for the addition of caustic soda
ensure that all of the aluminum compound
contained dissolved.
· Hot solution, which becomes a solution of sodium aluminate,
passed through several flash tanks that reduce
merocovery pressure and heat that can be reused
for the purification process.
· The solution is pumped into the settling tank.
on this tank, impurities will precipitate insoluble
under the tank. So that the solution contains only
aluminum oxide dissolved in caustic soda. Residue
which is under the tank (the so-called "Red Mud")
containing fine sand, iron oxide, oxide - oxide of
trace elements such as titanium.
· After impurities deposited, the liquid is left (with
physical forms such as coffee), is pumped into a series of filters.
Beberpa fine particles of impurities are left pada7
solution will be caught by the filter. This material will be washed
to obtain alumina and caustic soda that can be
reused during the process.
· Already filtered liquid is pumped into the tank six-storytall precipitation. Seed crystals of alumina hydrate (alumina
which binds water molecules) are added on top of the tank. Seed
Crystals will grow in line with the deposition of liquid
and alumina is dissolved will be bound in the crystal
occur.
· The precipitate that formed crystals in the bottom of the tank and then
moved. After washing, transferred to the dryer
for calcining (heating to remove water molecules
molecule bound to the alumina). Temperature range
2000 ° F (1.100 ° C) which will eliminate the water molecules,
so just stay Crystalline anhydrous alumina. Next
cristal flowed into the cooler for cooling and process
finishing.8
The Hall-Heroult process
In general in this process, fused alumina dielektrolisis, where
melt was mixed with the molten electrolyte in the pots kriolit
where the pot is bound by a series of carbon rods at the top
pot as a cathode. Carbon anodes are at the bottom of the pot as
pot lining, with a strong current flow 4-5 V between the anode and katodanya
electrolysis process occurs. Alumina disconnection of bonds due
electrolysis, molten aluminum will go down the pot, which
periodical will be accommodated into a cylindrical mold or
slabs. Each - each pot to produce 66.000 to 110.000 tonnes
aluminum per year (Anonymous, 2009). In general, 4 tons of bauxite will
produce 2 tons of alumina, which will produce 1 ton
aluminum (Ulucak, 2003)
Chemical reactions in general on the Hall-Heroult:
Prose Hall-Heroult By Gradual:
Molten alumina into aluminum metal to occur on steel
vat called a pot reduction. The bottom of the pot is coated / restricted
with carbon which acts as one electrode (conductor
electric current) from the system. Opposite electrode consists of a series of rods
carbon depending on the pot. Pot is structured in such a reduction
appearance, lined consisting of 50-200 pots are connected to one another
form electrical circuits.
• In a pot reduction, the crystals of alumina dissolved in molten
kriolit at temperatures of 1760-1780 ° F (960-970 ° C) so that
resulting electrolyte solution that will deliver listrik9
of carbon rod (Cathode) menujuu-Carbon Layers
(Anode). DC current (4-6 volts and amperes 100000-230000)
melaului flow solution. so that a reaction will occur
will decide aluminum bonding with oxygen on
molecule of alumina. Oxygen is released bound
carbon rod (Cathode), thus forming carbon
dioxide. Pure aluminum deposited at the bottom of the pot as
molten metal.
· Process continued consolidation, with the addition of alumina
the solution to replace compounds kriolit
decomposes. Electric current flows remain constant. Hot
derived from the flow of electricity to keep the contents of pot remain
is in a liquid state. Pure aluminum melt
collected under the pot
· Molten under pots, collected. Accommodated
the mold (rod or plate). When the flow
kecetakan flow, the outer mold is cooled with
water flow, which causes aliminium become solid.
Solid pure metal can be formed by sawing
in accordance with kebutuhan.10
2.3 Use of Aluminium
Some use aluminum, among others:
1. Automotive industry sector, to create truck and component
motor vehicle.
2. to make the fuselage.
3. Housing construction sector; for doors and window frames.
4. Food industry sectors, for packaging various types of products.
5. Other sectors, eg for electric cables, furniture and household
handicrafts.
6. Make thermite, a mixture of aluminum powder with iron powder
(III) oxide, is used to weld steel in place, for example for
connecting railroads. Some Aluminum compounds are also many
use, among others:
1. Tawas (K2SO4.Al2 (SO4) 3.24H2O)
Alum has the chemical formula KSO4.AL2. (SO4) 3.24H2O. Alum
used to purify drinking water in water treatment.
2. Alumina (Al2O3)
Alumina is divided based on alpha-and gamma-allumina allumina. Gammaalumina obtained from heating Al (OH) 3 under 4500C. Gammaalumina used for the manufacture of aluminum, for toothpaste, and
industrial ceramics and glass industries. Obtained from Alfa-allumina
heating Al (OH) 3 at temperatures above 10000C. Alfa-contained allumina
as corundum in nature that are used for sandpaper or Grinding. Stone
noble, such as rubies, sapphires, ametis, and topaz is an alpha-allumina
compounds containing transition metal element that gives color to the stone
them. Ruby colors include:
- Rubi red because they contain compounds of chromium (III)
- Sapphire blue because they contain compounds of iron (II), iron (III) and
titan (IV)
- Ametis violet color because they contain compounds of chromium (III) and
titan (IV)
- Topaz yellow because they contain iron (III) 11
The use of aluminum because aluminum is widely have better properties than other metals such as:
- Lightweight: weighs about 1 / 3 of the weight of iron and steel, or
copper and hence widely used in the transportation industry
such as air transport.
- Strong: especially when combined with other metals. Used
manufacture products that require high strength such as: aircraft
aircraft, ships, pressure vessels, vehicles and others.
- Easy set up with all the metal working process. Easy
assembled because they can be connected to the metal / other material through
welding, brazing, soldering, adhesive bonding, mechanical connections, or
with other grafting techniques.
- Good corrosion resistance: its durabel so well used to
influenced by environmental elements such as water, air, temperature and
Other chemical elements, either in space or even to
seabed.
- Electric conductors: every one kilogram of aluminum can
deliver an electrical current is twice as large when compared with
copper. Because aluminum is relatively inexpensive and lightweight, the aluminum
excellent for overhead electric cables and underground.
- Conductor's hot: This is very good properties for use in machineries / heat transfer equipment so as to provide savings
energy.
- Reflects the light and heat: It can be made in such a way
so having a high reflective capability that is about 95%
compared with the power of reflection of a mirror. This reflective nature
makes aluminum very good for heat radiation shielding equipment.
- Non-magnetic: and therefore very good for use on
electrical / electronics, radio transmitters / TV. and others, where
magnetization factor required negatif.12
- Not toxic: and therefore very good for use on
food industry, beverages, and drugs, namely untuik container and
wrapper.
- Has good toughness: in a cold state and not
such as other metals which become brittle when cooled. This property is
good for use in processing and transportation of LNG where
LNG liquefied gas temperatures can reach below -150 oC.
- Interesting: and therefore aluminum is often used without being
finish the process. Aluminum surface looks very attractive and
therefore suitable for furniture (decoration), building materials and automobiles.
Besides, aluminum can be given a surface treatment, can be glazed,
brushed or painted with various colors, and also given the anodizing process.
This process produces a layer that can also protect the metal from
scratches and other types of abrasion.
- Able to be reprocessed in order that the return process
through the melting process and then formed into products such as
the desired process of re-use can save energy, capital and
valuable raw material.
Metal surface covered by a thin layer of aluminum oxide
protect the metal to air, so the aluminum metal does not react
with air. Aluminum when burned in oxygen will produce
Al2O3 mambentuk white flame.
With a layer of aluminum is often used for coating other metals
so that no corrosion occurs on metal tersebut.13

III.END

3.1Kesimpulan
Aluminum is one of the elements that are very
abundant in nature. Although sangt abundant, not aluminum
never found in pure metallic form, but
always fused with the elements - other elements to form
mineral compounds. Minerals of the most common aluminum
found is bauxite. Where bauaksit contains
aluminum oxide and some trace elements that bind
chemically. To obtain pure aluminum metal from
minerals, required further processing. Processes
most common way to obtain aluminum metal from the mineral
bauxite is through 2 stages of the primary process. That process
Bayer to produce pure aluminum oxide (alumina) from
bauxite. The next process called the Hall-Heroult process by which
the electrolysis process is carried out by modification
thermochemical to produce pure aluminum from alumina.

Aluminum Melting Process

In the smelting process used krusibel kitchen. The material used is a scrap of Al results of research students. The first thing done is the kitchen preparation process. Starting from the melting furnace cleaning and coating with a coating to the placement of coal briquettes in large furnaces.

During the smelting process, material, Al is used to process pre-heating. It aims to eliminate moisture on the surface of the material to avoid gas formation and dissolution in the molten metal that can cause gas defects. After the pre-heating the metal material is inserted into the furnace and allowed to melt. During smelting coal briquettes continuously added to maintain a stable supply of heat to melt metal.

i. Alloying

In the casting process where the addition is intended to produce products that comply with the dimension values ​​are also needed mechanical properties of materials as appropriate. Provision of additional material (alloying) aims to improve the mechanical properties of the material price. For Al granting alloying material using the material of Cu, Zn, Mg, P, Si, Sr, and Na.

In this lab strengthening of alloying is not performed. If it is done and then the samples tested (tensile, hard) then produced a greater value than without alloying.

ii. Degassing

At high temperature hydrogen gas will tend to diffuse into the molten metal. Hydrogen gases must be removed from molten aluminum because it will lead to defects in the body cast. This process is called process gas expenditure degasser. Generally degasser used was in the form of tablets or a gas (argon gas and nitrogen gas).Mechanism of gas expenditure on liquid aluminum metal are as follows:

Tablets are inserted into the molten aluminum will produce gas in the form of a nearly empty air bubbles (<1 atm). Hydrogen gas dissolved in the aluminum can not get out because the pressure inside the molten aluminum <<1 atm while the outside pressure of 1 atm. As a result of air bubbles produced tablets into hydrogen gas and air bubbles are carried upwards bersaman with other impurities dissolved in liquid aluminum. Gas-gas or air bubbles that some will become dross, and will be disposed of through a disposal process dross. In this lab degasser is not used.

iii. Cover Flux

Once the process is complete degasser proceed with the process of flux. The process of flux aims to cover or covering the surface of molten aluminum metal to avoid the entry of hydrogen gas into aluminum metal. Giving flux made at the time began melting aluiminium flux by sprinkling on the surface of liquid aluminum. Covering flux serves for covering the surface of molten metal to avoid the entry of hydrogen gas. Giving flux of this type carried out without stirring. At the lab used flux covering.

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