Question

State the function of 

1. NaOH 

2. cryolite 

3. fluorspar in the metallurgy of aluminium.

Answer 1

Functions of : 

(i) NaOH : Crushed and powdered bauxite is heated with a cone, solution of NaOH at 150-200°C for 2 hours under pressure. The main impurities present in bauxite (Fe₂O₃ and SiO₂) remain unaffected with cone. NaOH since these are not amphoteric. Bauxite, being amphoteric reacts with the base to form sodium aluminate, which is soluble in water. Thus NaOH helps in the purification of the ore. 

(ii) Cryolite : 

(a) To increase the mobility of the fused mixture. 

(b) To lower the fusion point of the mixture. 

(c) To increase the electrical conductivity of the mixture. 

(iii) Fluorspar : 

(a) To increase the mobility of the fused mixture

(b) To lower the fusion point of the mixture.