Why is limestone used in the iron extraction process?
Iron ore is burned with coked coal which is almost pure carbon. This produces enough heat to melt the iron ore which is mostly Fe2O3, and the coke supplies carbon (along with air added to the mix) along with oxygen in short supply to make carbon monoxide, which is the agent responsible for reducing the Fe2O3 to pure iron. The oxygen must be removed to get the Fe. The main chemical reaction producing the molten iron is: Fe2O3 + 3CO → 2Fe + 3CO2 Limestone is calcium carbonate. CaCO3 is added to the melted mix, the reaction is: CaCO3 → CaO + CO2. The calcium oxide formed by decomposition reacts with various acidic impurities in the iron (notably silica), to form the slag which is essentially calcium silicate, CaSiO3. This is lighter than the iron and floats the impurities of the iron to the top of the molten metal to be skimmed off.
