Describle the principal controlling each of the following processes:
(i) Preparation of cast iron from pig iron.
(ii) Preparation of pure alumina `(Al_(2)O_(3))` form bauxite ore.

Explanation

(i) Pig iron: The iron obtained from blast furance is called pig iron. It is impure form of iron contains 4% carbon and small amount of S,P, Si and Mn .It can be casted into variety of shapes.
(ii) The principal ore of aluminium is bauxite `Al_(2)O_(3).xH_(2)O`
Leacing of alumina form bauxite: Bauxite, usually contains `SiO_(2)`, iron oxides and titanium oxide `(TiO_(2))` as impurities. Concentration is carried out by the degesting the powdered ore with concentrated solution of `NaOH` at 473-523 Kand 523 K and 35-36 bar pressure.The `Al_(2)O_(3)` is leached out as as sodium aluminate.
`Al_(2)O_(3)(s) + 2NaOH(aq) + 3H_(2)O(l) to underset("Sodium aluminate")(2Na [Al(OH)_(4)])(aq)`
The sodium aluminate is solution is neturealised by passing `CO_(2)` gas and hydrated `Al_(2)O_(3)`
`underset("hydrated alumina")(Al_(2)O_(3).H_(2))O(s) overset(1470k)to Al_(2)O_(3)(s)+ underset("pure alumina")("x"H_(2)O(g))`