- Source of metal: Metals occur in Earth’s crust and in seawater; in the form of ores. Earth’s crust is the major source of metal. Seawater contains many salts such as sodium chloride, magnesium chloride, etc.
- Mineral: Minerals are naturally occurring substances which have a uniform composition.
- Ores: The minerals from which a metal can be profitably extracted are called Ores.
Metals found at the bottom of reactivity series are least reactive and they are often found in nature in free-state; such as gold, silver, copper, etc. Copper and silver are also found in the form of sulphide and oxide ores.
Metals found in the middle of reactivity series, such as Zn, Fe, Pb, etc. are usually found in the form of oxides, sulphides or carbonates.
Metals found at the top of the reactivity series are never found in free-state as they are very reactive, example; K, Na, Ca, Mg and Al, etc.
Many metals are found in the form of oxides because oxygen is abundant in nature and is very reactive.
Extraction of Metals: Metals can be categorised into three parts on the basis of their reactivity: Most reactive, medium reactive and least reactive.
The three major steps involved in the extraction of a metal from its ore are
- Concentration or enrichment of ores.
- Conversion of concentrated ore into crude metal and,
- Refining of impure or crude metal.
1. Concentration of Ores:
Removal of impurities, such as soil, sand, stone, silicates, etc. from mines ore is known as Concentration of Ores.
Ores which are mined often contain many impurities. These impurities are called gangue. First of all, concentration is done to remove impurities from ores. The concentration of ores is also known as enrichment of ores. Process of concentration depends upon physical and chemical properties of ores. Gravity separation, electromagnetic separation, froth flotation process, etc. are some examples of the processes which are applied for concentration of ores.
2. Conversion of Concentrated Ore into Crude Metal
Conversion of metals ores into oxides: It is easy to obtain metals from their oxides. So, ores found in the form of sulphide and carbonates are first converted to their oxides by the process of roasting and calcination. Oxides of metals so obtained are converted into metals by the process of reduction.
- Roasting: Heating of sulphide ores in the presence of excess air to convert them into oxides is known as Roasting.
- Calcination: Heating of carbonate ores in the limited supply of air to convert them into oxides is known as Calcination.
Calcination | Roasting |
(i) It is done for carbonate ores. | (i) It is done for sulphide ores. |
(ii) Carbonates ores heated in the absence of oxygen. | (ii) Sulphide ores are heated in the Presence of oxygen. |
(iii) The CO2 gas is released and Metal oxide is obtained. | (iii) SO2 gas is released and Metal oxide is obtained. |
