Metals are found in the Earth's crust either in a pure form or in compounds with other elements. Unreactive metals like silver and gold can be found in a pure form, while more reactive metals such as aluminium and magnesium are usually found combined with other elements in minerals. An ore is a rock that contains enough of a metal to make it worthwhile to extract. Some examples of ores are malachite, which contains mostly Copper Carbonate (Cu (03)), haematite, which contains mostly Iron (III) oxide (Fe₂O3), and bauxite, which contains mostly Aluminium oxide (Al2O3).
Extraction Methods
There are three main methods for extracting metals from their ores:
- Heat in air - used for less reactive metals
- Conversion of compounds of more reactive metals to metal oxides, followed by roasting with carbon or carbon monoxide to remove the oxygen
- Electrolysis of the molten ore, used for the most reactive metals
Reduction with carbon and carbon monoxide involves using these substances to reduce metal oxides. Carbon and carbon monoxide are more reactive than the metal displacement, allowing them to remove the oxide from the metal oxide. An example of this process is the reduction of zinc oxide with carbon to produce zinc and carbon monoxide.
For metals that are more reactive than carbon, they cannot be displaced by carbon and must be extracted using electricity through a process called electrolysis of molten compounds. For the ionic metal compound to be extracted, it must be in a molten state for electricity to travel through it.
Extraction of Iron - Blast Furnace
In the extraction of iron, a blast furnace is used to heat the iron ore in a limited supply of air to produce molten iron. Waste gases are removed, and then the iron is formed and trickles down. This process is highly exothermic and produces blast of hot air in which solid molten slag is formed.
Uses of Metals
Metals have various uses depending on their properties and properties of their alloys. For example, aluminium is used for aircraft, bicycles, long-distance electrical cables, and cooking pans. On the other hand, copper is used for electrical cables, cooking utensils, and water pipes. Different types of steel also have specific uses based on carbon content and properties. For instance, low carbon steel is malleable and easily shaped, used for car paneling and domestic goods, while high carbon steel is very strong and is used for bridges and cutting tools.
Alloys and Electrolysis
Alloys are mixtures of two or more elements, where at least one element is metal. When pure metals are mixed to form an alloy, it disrupts the regular arrangement of atoms, making it harder for them to slide over one another, thus producing stronger and harder materials.
Electrolysis is a chemical change caused by passing an electric current through an ionic compound that is either molten or in aqueous solution. An electrolyte is a substance that undergoes electrolysis when electricity is passed through it using two electrodes. Carbon (graphite) is commonly used for electrodes because it conducts electricity and is fairly unreactive. Platinum can also be used in some cases.
Electrolysis of Molten Compounds
During the electrolysis of molten compounds, the flow of electricity causes the molten compounds to undergo changes. For example, in the electrolysis of molten lead (II) bromide, as soon as the solid lead bromide (PbBr₂) melts, the ions are free to move around, enabling the electrons to flow in the circuit. This results in the production of bromine gas at the anode and solid lead at the cathode.
