Aluminium:
Aluminium is a metal which has an atomic number 13 and a atomic mass of 27, the material has low density and is very shiny.Aluminium is the third most abundant metal found on earth and is the most abundant metal found in the earth's crust.
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Australia is the largest producer of bauxite, with five mines supplying around 23 per cent of global production. Currently five bauxite mines in Australia providing feedstock for the seven alumina refineries, which in turn supply alumina to the six Australian aluminium smelters and the export market. Australia is the largest producer of bauxite in the world, with 74.9 million tonnes produced in 2011.
Five Australian Bauxite mines are:
Boddington (Western Australia) - BHP Billiton - Worsley AluminaGove (Northern Territory) - Pacific AluminiumHuntly (Western Australia) - Alcoa of AustraliaWillowdale (Western Australia) - Alcoa of AustraliaWeipa (Queensland) - Rio Tinto Alcan
Metals and Reactivity Series:
When extracting a metal from its ore the method used for the extraction depends upon the reactivity of the metal. The reactivity of a metal is understood by Looking at the Reactivity series given below:
The reactive metals are separated using Electrolysis.ELectrolysis is a process used to extract metals from their ores using direct current which produces chemical decomposition thereby separating the metal of interest.
Extraction of Aluminium:
From the reactivity series it can be observed that Aluminium is a reactive metal and therefore Electrolysis is used for the extraction of Aluminium from its ore.Aluminium oxide (Alumina) is used for the extraction of Aluminium by the Hall-Heroult Method.
Hall Heroult Method for the extraction of Aluminium:
Electrolytic Cell:
The cell is a steel tank lined with refractory bricks.The Cell has a carbon cathode and anode. The Cathode is carbon lining around the internall walls of the electrolytic vessel. Anode are the carbon rods which are dipped into the electrolytic vessel submerged in the electrolyte. The cell operates at a low voltage of about 5 - 6 volts, but at huge currents of 100,000 amps or more. The heating effect of these large currents keeps the cell at a temperature of about 1000°C.
Electrolyte for the Electrolysis:
For the electrolysis to happen an electrolyte is required here molten raw Alumina is needed.The temperature required melt Alumina is about 2040°C. This is an important issue which would make the extraction process very expensive to circumvent this problem CRYOLITE ( Na3AlF6) was added to reduce the temperature to about 980 °C to melt the solids. This saves a lot of energy.
Electrolysis:
The molten mixture is then electrolysed with a very large current and the aluminium ions are reduced to form aluminium metal (at the cathode) and oxygen gas is formed at the anode, at the anode Oxygen reacts with the carbon (anode is made of Carbon) from to give carbon dioxide gas.
Reaction at Electrodes:
At cathode:
Aluminium is released at the cathode. Aluminium ions are reduced by gaining 3 electrons.
Al+3 + 3 el- --------> Al
At Anode:
Oxygen is produced initially at the anode.4O-2 ----------> 2O2 + 4 el-
However, at the temperature of the cell, the carbon anodes burn in this oxygen to give carbon dioxide and carbon monoxide.
Uses of Aluminium:
1) Low density and strength make aluminium ideal for construction of aircraft, lightweight vehicles, and ladders. An alloy of aluminium called duralumin is often used instead of pure aluminium because of its improved properties.2) Easy shaping and corrosion resistance make aluminium a good material for drink cans and roofing materials. 3) Corrosion resistance and low density leads to its use for greenhouses and window frames.4) Good conduction of heat leads to its use for boilers, cookers and cookware.5) Good conduction of electricity leads to its use for overhead power cables hung from pylons(low density gives it an advantage over copper).
Potential depletion of Aluminium:
It has be suggested that all known economically workable deposits in Australia will be exhausted in 2139 due to excessive mining.The depletion of nonrenewable resources such as bauxite (to make aluminum), used in many electronic gadgets including smart phones as well as smart bombs is a problem of great importance.
Alternatives:
Recycling is one of the best alternative to overcome the depletion problem in the near future.Aluminium recycling is the process by which scrap aluminium can be reused in products after its initial production. The process involves simply re-melting the metal, which is far less expensive and energy intensive than creating new aluminium through the electrolysis of aluminium oxide (Al2O3).Members of the family of composite materials, glass/carbon fibre reinforced epoxies can be used to replace Aluminium, as they are stronger than Aluminium. Stone and wood,and cement could be used to replace Aluminium metal. Stone and concrete have similar properties, but concrete is much easier to use: one can pour it into moulds to create any shape.The best way to preserve the existing Aluminium resources is Recycling.
en.wikipedia.org/wiki/Aluminium
