CBSE Class 6 Answered

1. 1.    Concentration by gravity separation

The powdered ore is washed with a stream of water. As a result, the lighter sand particles and other impurities are washed away and heavier ore particles settle down.

1. 2.    Roasting and calcination

The concentrated ore is strongly heated in a limited supply of air in a reverberatory furnace. As a result, moisture is driven out and sulphur, arsenic and phosphorus impurities are oxidised off.

1. 3.    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.

i.   Lower region (combustion zone) - Temperature is at 1500°C.

1. i.    Middle region (fusion zone) - Temperature prevails at 1000°C. 

1. i.     Upper region (reduction zone) - Temperature prevails at 400°C.

The iron thus formed is called pig iron. It is remelted and cast into different moulds. This iron is called cast iron.