`=>` A few elements like carbon, sulphur, gold and noble gases occur in free state while others in combined forms in the earth’s crust.

`=>` The extraction and isolation of an element from its combined form involves various principles of chemistry.

`=>` A particular element may occur in a variety of compounds.

`=>` The process of metallurgy and isolation should be such that it is chemically feasible and commercially viable.

`=>` Some general principles are common to all the extraction processes of metals.

`text(Minerals :)` These are naturally occurring chemical substances in the earth’s crust obtainable by mining.

`text(Ores :)` Minerals in which a metal may be found, only a few are viable to be used as sources of that metal. Such minerals are known as ores.

`=>` Rarely, an ore contains only a desired substance. It is usually contaminated with earthly or undesired materials known as `text(gangue)`.

`=>` The extraction and isolation of metals from ores involve the following major steps :

• Concentration of the ore

• Isolation of the metal from its concentrated ore and

• Purification of the metal.

`text(Metallurgy :)` The entire scientific and technological process used for isolation of the metal from its ores is known as metallurgy.

`=>` Elements vary in abundance.

`text(Aluminium :)`

●Among metals, aluminium is the most abundant.

● It is the third most abundant element in earth’s crust (8.3% approx. by weight).

● It is a major component of many igneous minerals including mica and clays.

● Many gemstones are impure forms of `Al_2O_3` and the impurities range from `Cr` (in ‘ruby’) to `Co` (in ‘sapphire’).

`text(Iron :)`

● Iron is the second most abundant metal in the earth’s crust.

● It forms a variety of compounds and their various uses make it a very important element.

● It is one of the essential elements in biological systems as well.

`=>` The principal ores of aluminium, iron, copper and zinc have been given in Table1.

`=>` For the purpose of extraction, bauxite is chosen for aluminium.

`=>` For iron, usually the oxide ores which are abundant and do not produce polluting gases (like `SO_2` that is produced in case of iron pyrites) are taken.

`=>` For copper and zinc, any of the listed ores (Table1) may be used depending upon availability and other relevant factors.

`=>` Before proceeding for concentration, ores are graded and crushed to reasonable size.