1. The iron obtained by smelting (extraction of metal by heating and melting) it in blast furnace is called pig iron. Pig iron (having carbon content from 3.8-4.7 %) is melt with scrap iron and coke using hot air blast. In this way, cast iron is prepared. Due to this, impurities such as C, S and P present in the pig iron are removed as CO2, SO2 and P2O5 and carbon content reduced to about 3%. It is extremely hard and brittle.
2. The principal ore of aluminium is bauxite Al2O3.xH2O. Bauxite is concentrated by digesting the powdered ore with concentrated solution of NaOH at 473-523K. The Al2O3 is leached or drained out as sodium aluminate. The sodium aluminate is neutralized by passing CO2 gas and hydrated Al2O3 is precipitated which is filtered, dried and heated to give pure Al2O3.
The basic principle lies that bauxite is soluble in concentrated NaOH solution whereas the impurities are not. The reactions are as follows:
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