EXTRACTION OF METALS FROM THEIR ORES.

Many metals in the earth’s crust are too reactive to exist on their own, and they occur naturally in rocks as compounds such as carbonates and oxides.

          There are however some exceptions, such as gold and silver, which occur natively and are known as free metals. They are very unreactive and have survived thousands of years without reacting with substances to become compounds.

How metals are extracted from the earth’s crust depends on the position on the reactivity series.

EXTRACTION OF REACTIVE METALS

The higher up the reactivity series the metals are the more reactive they are and therefore they are harder to be extracted from the earth’s crust. For example Aluminium which is the most abundant metallic element in the Earth’s crust.

          Aluminium is very difficult to react because it holds on tightly to the element(s) it has combined with and is extracted from its ore by electrolysis. This is a process of splitting up substances by passing an electric current through them. The substance, which decomposes, is called the electrolyte. During this process the metal is produced at the cathode, the negative electrode which attracts the cations, while the non-metal is produced at the anode, the positive electrode which attract the anions. In order to extract aluminium from its ore involves the electrolysis of aluminum oxide. This process involves Bauxite, an impure form of aluminium, which is treated with sodium hydroxide to remove the impurities. Then the aluminium oxide is dissolved in molten cryolite to reduce the temperature and the molten mixture is then electrolysed in a cell.  This process however is very expensive and in order to keep the cost low regions were this process is used, hydroelectric power is used to generate electricity.

EXTRACTION OF UNREACTIVE METALS.

The further down the reactivity series the metals are the easier it is for them to be extracted. For example copper which is free metal and is mainly extracted from copper pyrites. The copper ore is crushed and is then concentrated by froth flotation. A collector is added to the ore mixture and the collector sticks to the surface of the copper pyrites particles giving it water repellant. Then a detergent is added along with air to make the substance froth. The copper pyrites particles are concentrated in the froth and can easily be removed. They are then roasted in a limited supply of air to make sure conversion of copper pyrites to copper (I) sulphide.  The copper (I) sulphide is then reduced to copper by heating a controlled amount of air, and the copper is the refined by electrolysis.

 THE REACTIVITY SERIES

By Therese Morrow: Loreto College, Coleraine.