Rocks that contain enough of a metal or a metal compound to make it worth extracting are called ores. A few very unreactive metals like gold are found native as metals. Gold can be seperated from rocks by physical methods. However, most metals are found as compounds and so have to be extracted using chemical reactions.
- Metals can be extracted from compounds by displacement, using a more reactive element are by electrolysis.
- Metals that are less reactive than carbon can be extracted by heating with carbon to reduce their oxides. (Reduction is the removal of oxygen from a compound.) This method is used commercially if possible.
We extract metals from their oxides, metal oxides are metals which are bounded with oxygen.
An iron ore is made up of iron and oxygen.
Many of the ores used to produce iron contain iron (3) oxide. Iron is less reactive than carbon and so it can be extracted from its ore using carbon.
Iron is extracted in a blast furance using coke to provide the carbon. The iron oxide is reduced at high temperatures by carbon.
The iron produced contains about 4% impurities that makes it hard and brittle. Its properties mean that it has only a small number of uses as cast iron. However, it is the starting materail for making steels.
Properties of Iron and Steels
- Pure iron has a regular arrangement of atoms. The atoms are in layers that slide over each other easily, so its shape can be changed. It is also a soft metal and bends easily.
- Steels are alloys of iron - they are mixtures that contain other elements as well as iron. The other elements change the regular structure of the metal and this changes its properties.
- Carbon steels contain small amounts of carbon, up to 1.5%. Increasing the amount of carbon in the steel makes it harder but more brittle.
- Low-alloy steels contain up to 5% of other metals to give them special properties.
- High-alloy steels contain a higher percentage of other metals, for example stainless steel contains about 25% chromium and nickel, so it doesn't rust.
Alloys in Everyday Use
Many pure metals are too soft and lose their shape to easily. Mixing a pure metal with other metals or elements to make an alloy makes the metal harder. Alloying may also affect other properties of the metal, such as strength, appearance and resistance to corrosion. Ths cost of an alloy depends on the cost of the metals it contains.
Alloys are mixtures, this means that the amounts of the elements they contain can be varied so they can be disigned with s specific properties for a particular use.
Shape meomory alloys are smart because they return to their original shape after they have been bent.
The elements between group 2 and 3 in the periodic table are all metals and are called 'transmition metals.'
- They are good conductors of heat and electricity.
- They are strong, hard and dense, but can be bent or hammered into shape.
- Except for mercury, transmition metals have high melting points.
Transmition metals have many simialr properties but there are differences that make them useful for specific purposes. Copper is particularly useful for plumbing and electrical wires as it is a good conductor of electricity and is not corroded easily. Copper is processed by smelting and electrolysis. Little high-grade copper ore remains, so huge amounts of rocks have to be moved in open cast mines. New methods of extracting copper are being developed, including using fungi, bacteria and plants. Extracting copper in the traditional way is expensive and affects the enviorment.
Aluminium and Titanium
We use aluminium and titanium where low density and resistance to corrosion are important as they have a smaller density than other metals and titanium is strong at high temperatures. Both metals form oxide layers that protect them from further corrosion.
- Alminium is soft and quite a low melting point but can be hardened by alloying.
- Titanium reachts with carbon and so is extracted by displacement with a reactive metal, e.g sodium.
- Aluminium and sodium are too reactive to extract with carbon and so electroysis is used, with high costs of energy.
- Aluminium is widely used in buildings, cans, cooking foil, electricty cables and aircraft.
- Titanium is used in jet engines, nuclear reactors, replacement hip joints and bicycles.
Recycing metals aviods mining and processing metal ores.