Question

What is Slag? explain with an example.

Answer 1

Hint: Minerals/ metals are obtained from their respective ores via various chemical processes. An ore consists of other unwanted impurities called the gangue. To remove the gangue a cleaning or purifying agent is added to it. The mixture formed from gangue and flux is termed slag.

Complete answer:
Metals like iron, copper, and lead are present in the form of ores. They consist of impurities and silicates of some other metals. To remove the impurities, the ore is smelted at a high temperature. Smelting eliminates the undesired substances from the ore.
Slag is formed as a by-product during processes like smelting or other combustion and metallurgical processes. The gangue present is treated with flux to form the fusible slag. Slag is mainly the oxides of elements like sulphur, phosphorus, silicon, and aluminium. It can also be in the form of metal phosphates or silicates.
The molten metal is separated from the impurities as slag is formed. It floats on the surface of the metal above, to prevent the metal from coming in contact with the atmosphere. Slag doesn’t allow the metal to get oxidized. The slag looks like glass which can be reused to make concrete for road building. If the slag has phosphate content it can be supplied as a plant fertilizer.
Examples of Slag:
-Alumina and silica
In the making of steel, CaO and $MgCO_3$ are introduced into refractories to neutralize alumina and silica in the metal. They also help to remove the phosphorus and sulphur Impurities.
-Iron and silica
These are obtained as slag during the smelting of copper and lead.

Note:
Sometimes the slag obtained is more valuable than the molten metal. For example, Ilmenite is a titanium-iron oxide mineral from which titanium oxide has to be prepared. The slag produced in this smelting is more valuable than the metal.