Iron is made from its ore in a blast furnace. The iron ore has an impurity called X. To remove X, another chemical, Y, is added to the mixture. The chemical Y is calcium carbonate (CaCO3). When Y is heated (∆), it breaks down into calcium oxide (CaO) and carbon dioxide (CO2) :
‌
CaCO3
(Y)
∆
‌───────▶‌
CaO+CO2 Next, calcium oxide (CaO) reacts with the impurity, silicon dioxide (SiO2), which is X, to form a liquid waste called slag:
CaO+‌
SiO2
(‌ Impurity X ‌)
→‌
CaSiO3
(‌ Slag ‌)
So, X is silicon dioxide (SiO2), and Y is calcium carbonate (CaCO3).