Introduction to Metallurgy

Metallurgy: It is the branch of chemistry that deals with the extraction of metals from their ores and utilizing them for useful purposes.

Metallurgy process includes the following operation.

1. Mining: Getting out the ore out of ground
2. Crushing and grinding: Ores are broken up to small pieces.
3. Concentration: Removal of gangue or matrix
4. Refinity: To obtain a pure metal.

Ore: Ore are those minerals from which an element can be extracted conveniently and economically. Example: Bauxite (aluminum), Hematite (Iron) etc.

Minerals: All naturally occurring compounds in the earth crust from which metal can be extracted are called minerals.

Note: All the ores are minerals but all minerals are not ore. It is because, ores are the minerals form which the metals can be extracted economically. Let’s take an example: Bauxite and clay both are the minerals of aluminum. Though aluminum can be extracted from clay, but not in convenient and economical way. So, clay cannot be considered as ore.  But it is a mineral since aluminum can be extracted from clay.

Gangue or Matrix: The unwanted impurities present in ores are called gangue or matrix.

Flux: It is a substance that chemically combines with gangue which may still be present in the roasted ore or calcinated ore to form an easily fusible material called slag.

There are two types of flux:

1. Acidic flux: It is an acidic oxide like SiO2, P2O5 etc that are used to remove the basic impurities. For example: $$\ce{SiO2 + FeO -> FeSiO3}$$
2. Basic flux: It is a basic oxide like CaO, MgO, FeO etc that are used to remove the acidic impurities. For example: $$\ce{CaO + CaO -> CaSiO3}$$

Slag: It is a fusible mass formed by the combination of a flux with infusible impurities of the concentrated ore at high temperature. It is usually a double salt.

$$\ce{SiO2 + CaO -> CaSiO3}$$

So, where SiO2 is a impurity, CaO is flux and CaSiO3 is a slag.

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