Question

Haematite, the ore of iron undergo roasting.

a. Which impurity is not removed by this method? 

b. How is it removed then? Explain.

Answer 1

a. Silicon dioxide (SiO₂)

b. It is removed during metallurgy. At high temperature, CaCO₃ (limestone) decomposes to form CaO, which is the flux. 

CaO combines with SiO₂ and forms CaSiO₃ (slag).

CaCO_3(s) → CaO_(s) + CO₂(g)

CaO_(s) + SiO_2(s) → CaSiO_3(s)