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Question: What can you tell me about the three most common metals used in Britain, i.e. aluminium, copper and iron? How are each of these metals formed and what are their uses?  






1. Aluminium

(a) How formed (occurrence):

Aluminium is the most abundant metal in the earth's crust. Its compounds are found in clay and many rocks. Metallic aluminium has been in use for a little over a hundred years, despite there being so much of it. Its discovery took a long time because it is always found combined with something else. Aluminium silicate is a common form, as are silicates of aluminium mixed with other metals, such as calcium, iron, magnesium, potassium or sodium. Extracting the aluminium is not worth the cost as these silicate ores are of no use.
Aluminium is commercially extracted from an ore called bauxite, which is aluminium oxide. It is extracted from the bauxite in a process called the Hall-Heroult Process, where an electric current is passed through aluminium oxide or alumina (bauxite with the impurities removed) which has been dissolved in melted cryolite. This liquid conducts electricity and passing a current through it allows aluminium to be deposited at the cathode (negative terminal) of the cell. The aluminium is about 99.5% pure.

(b) Uses:

Aluminium is a good conductor of heat and because of this has been used widely in cookery. It is second only to copper as a conductor of electricity, but is much lighter and so many electric power lines use aluminium wires particularly for high voltage transmission (over 700 000 volts).
Aluminium foil is in widespread use in the kitchen and as an insulator in homes. It is used in bottles and cans, which raises the issue of aluminium recycling.
Because aluminium is light and strong it is used in the construction industry and low temperature nuclear reactors as it absorbs relatively few neutrons. It is corrosion resistant and has boat and marine applications.
When mixed with other metals e.g. magnesium, to form an alloy it can be used in planes and trains.

2. Copper

(a) How formed (occurrence):

Native copper is still found in many parts of the world, in particular Michigan, U.S.A. It is extracted from mines, some of which are around 1.6 km deep. When it comes from the mines it contains various rock substances. These are removed by crushing with hardened steel weights. The native copper is gathered by washing away the lighter earth particles with a fast flowing stream of water. This is known as concentrating as it increases the amount of copper in the ore. This ore is now mixed with coke and limestone and in a blast furnace process the molten copper is left at the bottom of the furnace in a pool. This is then refined further by a process of electrolysis so the copper can be used commercially.
In addition to native copper, there are other ores such as chalcocite, chalcopyrite, cuprite. Copper is extracted from chalcocite (a sulphide ore) by a method called the oil-flotation process. In this, pulverised ore, water and low grade oil are mixed in large tanks. Air is blown through the tanks and froth collects on the top. Copper sulphide particles stick to the froth and heavy rock sinks to the bottom. This copper sulphide ore is heated in air and most converted to copper oxide. Heating the ore with limestone then removes the silica as slag which floats on top of the molten copper oxide-sulphide mixture. Air is blown through the molten mixture in a furnace and the copper oxide reacts with the copper sulphide to form metallic copper and sulphur dioxide gas. To remove impurities the copper is further refined by electrolysis and is then about 99% pure.

(b) Uses:

Copper has been used since prehistoric times for coins, ornaments and cooking utensils. It was also used to cover the bottom of wooden ships as protection. Alloyed with tin, it makes bronze which is stronger than pure copper and could be used as a cutting tool as in the bronze age. Brass which includes zinc is another hard alloy of copper.
Copper is easily bent and stretched and has good corrosion resistance and is a good conductor of electricity. Because of this it is used mainly in the electricity industry in outdoor power lines and cables, house, generators, electro-magnets and various communications devices. Some roofs have been made of copper as have many water pipes.

3. Iron

(a) How formed (occurrence):

Greenland is one of the few places where iron is found in the free state. It is found as an alloy with nickel in meteorites. Iron is mainly found as an ore and ranks second to aluminium in its total abundance. The most common iron ore is hematite which is reddish brown in colour. Less important ores are limonite, magnetite and siderite. Iron pyrites sometimes called " fool's gold" is a sulphide of iron which can be used in the production of sulphuric acid. Supplies of iron ores are essential as iron is used to make steel.
hematite is converted to pig iron in a blast furnace by using coke and calcium carbonate.

(b) Uses:

Iron is the most common and most useful of all metals. It is highly magnetic and is the basis of steel, an alloy with carbon and other elements. A great deal of iron is also used as wrought iron and cast iron. Iron is also used for producing galvanised sheet metal and electro-magnets.
Iron is an essential part of haemoglobin. This is the molecule in red blood cells responsible for carrying oxygen to all parts of the body. Where a person is short of iron they are anaemic and iron compounds are used as treatment. Iron is also used in tonics. 



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