Extraction of metals and Alloys.

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YEAR 11 CHEMISTRY

Extraction of metals and

 Alloys

What is an alloy?

An alloy is a mixture of metals, which may have different and improved qualities from metal elements, which make it. The percentage of elements in an alloy can be tailored to the application or purpose it is being made for. Usually an alloy is made of one metal (the base metal) with small amounts of other metals added. The other metals replace the position of the base metal in its structure.

Extraction of Metals

An element or a compound in nature inside the earth’s crust is called a mineral. They have a percentage of metal which can be extracted. This is called a metal ore. The most common metal ores are oxides and sulphides. Sulphides are the oldest ores. Oxides are formed when photosynthesis in plants release oxygen into the air. Metal ores are an infinite resource and once they are used, they are gone. Recycling helps this. Generally half of all metal is recycled through scrap metal facilities.

The Reactivity Series – (See appendix - diagram 1)

A metal that is under carbon in the Reactivity Series (zinc to silver) can be extracted from its ore by heating with carbon. Carbon is used as it is easily available and it’s cheap (coke and charcoal are both carbon). The metal is then reduced by the carbon. Hydrogen may be used to reduce other metals which are lower than it on the Reactivity Series. It is more expensive than carbon. It is only used for the extraction of tungsten. Gold and platinum are found naturally as elements and do not need to be reduced. Silver and copper are also naturally found.

Extraction of Metals and Alloying

Metal ores are found in the earth. They are rocks containing mineral or metal compounds or metals themselves and need to be extracted or removed from the rocks and the ground. To extract a metal from its ores you need to know its reactivity. The process involves a chemical reaction where the metal is separated from the other elements in the mineral.

History of Metal Extraction

Metals have been used by people for thousands of years. Gold and silver found in nature, were used for jewellery to show how wealthy people were. These two metals are too soft to be used as tools. The first useful metal discovered was bronze (the Bronze Age). Bronze was used a lot for tools and weapons in Asia and Africa from 4500 B.C. and in Britain from 2000 B.C. Bronze is not an element but an alloy of copper and tin. Ores of copper and tin can be reduced by heating with carbon. This would have happened as people lit wood fires in a place where tin and copper ore were. The burnt wood would have made the ores (copper and tin) into bronze.

After the Bronze Age, coal fires were used to produce enough temperature for the extraction of iron (hence the Iron Age) The Iron Age began in Asia and Africa in 1100 B.C and in Britain in 500 B.C. Metals above carbon in the reactivity series can only be extracted by electrolysis. With the discovery of electricity in the nineteenth century, this allowed the extraction of more reactive metals. Aluminium has been extracted since around 1870. (3000 years since they found iron and 6000 years since they found bronze).  

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Extraction of Aluminium

Aluminium is the third most abundant (plentiful) element in the Earth’s crust. It is more abundant and the more expensive to produce compared with iron. This is because it takes a lot of electricity for the extraction process of electrolysis to happen. Around half of aluminium used is recycled. It takes less energy to recycle aluminuim than to extract it from its ore. Handling costs of aluminuim in the recycling process adds to this. Aluminium is high in the Reactivity Series and is resistant to corrosion as a thin layer of aluminium oxide on its ...

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