Types of Corrosion:
(i) Dry Corrosion or Chemical Corrosion :
The corrosive action in the absence of moisture is called dry corrosion. It is the process of a chemical attack on a metal by a corrosive liquids or gases such as O₂, N₂, SO₂, H₂S etc. It occurs at high temperature.
(ii) Wet Corrosion or Electrochemical Corrosion: The corrosive action in the presence of moisture is called wet corrosion. It occurs as a result of electrochemical reaction of metal with water or aqueous solution of salt or acids or bases.

Chemical method or Leaching:
(i) This method is employed when the ore is in a very pure form.
(ii) The ore is treated with a suitable reagent such that the ore is soluble in it but the impurities are not. The impurities are removed by filtration.
(iii) The solution of the ore, ie., the filtrate is treated with a suitable reagent which precipitates the ore.

Smelting (in a Blast Furnace) :
The charge consisting of roasted ore, coke and limestone in the ratio 8:4:1 is smelted in a blast furnace by introducing it through the cup and cone arrangement at the top. There are three important regions in the furnace.

(a) The Lower Region (Combustion Zone) The temperature is at 1500°C. In this region, coke burns with oxygen to form CO₂ when the charge comes in contact with a hot blast of air.

It is an exothermic reaction since heat is liberated.
(b) The Middle Region (Fusion Zone) - The temperature prevails at 1000°C. In this region, CO₂ is reduced to CO.

Limestone decomposes to calcium oxide and CO₂

These two reactions are endothermic due to absorption of heat. Calcium oxide combines with silica to form calcium silicate slag.
CaO + SiO₂ ⟶ CaSiO₃
(c) The Upper Region (Reduction Zone) - The temperature prevails at 400°C . In this region carbon monoxide reduces ferric oxide to form a fairly pure spongy iron.

The molten iron is collected at the bottom of the furnace after removing the slag.
The iron thus formed is called pig iron. It is remelted and cast into different molds. This iron is called cast iron.

Bessemerisation The molten matte is transferred to Bessemer converter in order to obtain blister copper. Ferrous sulphide from matte is oxidized to ferrous oxide, which is removed as slag using silica.
2FeS+3O₂ ⟶ 2FeO+2SO₂ ↑

2 Cu₂S + 3O₂ ⟶ 2 Cu₂O + 2 SO₂

Froth floatation:
(i) Principle: This process depends on the preferential wettability of the ore with oil (pine oil) and the gangue particles by water. Lighter ores, such as sulphide ores, are concentrated by this method. E.g. Zinc blende ZnS

(ii) Method: The crushed ore is taken in a large tank containing oil and water and agitated with a current of compressed air. The ore is wetted by the oil and gets separated from the gangue in the form of froth. Since the 4 ore is lighter, it comes on the surface with the froth and impurities are left behind