Q.What is the role of quick lime in the extraction of Iron from its oxide Fe₂O₃?

Once an ore has been concentrated, extracting the crude metal from it always proceeds in exactly two steps, in this order: (i) converting the concentrated ore into an OXIDE of the metal of interest, and (ii) REDUCING that oxide down to the free metal. Every route goes through the oxide as an intermediate, even for a sulphide or carbonate ore, because thermodynamically the reduction of an oxide is generally easier than reduction of other compound classes.

Step 1: conversion to oxide. ROASTING is used for sulphide ores -- strongly heating the concentrated ore with EXCESS oxygen, below the metal's melting point, converting the sulphide to the oxide and releasing SO2 (e.g. 2PbS + 3O2 → 2PbO + 2SO2); roasting also volatilises impurities like arsenic, sulphur and phosphorus as their own oxides, and modern plants trap the SO2 by-product to make sulphuric acid. CALCINATION is used for carbonate/hydrated ores -- strongly heating in the ABSENCE (or with limited supply) of air, expelling CO2 from a carbonate (e.g. CaCO3 → CaO + CO2) or water of crystallisation from a hydrate (e.g. Fe2O3.3H2O → Fe2O3 + 3H2O), and leaving a porous oxide behind.

Step 2: reduction of the oxide. The choice of reducing agent depends on the metal's reactivity: carbon cannot reduce very reactive metals (Na, K, Al); CO cannot reduce ZnO or Al2O3. Five reduction routes: SMELTING (a flux + reducing agent, e.g. CaO flux combining with acidic silica gangue to form calcium silicate SLAG in iron extraction, Fe2O3 + 3CO → 2Fe + 3CO2; or, for copper from copper pyrites, an acidic silica flux forming ferrous-silicate slag while Cu2S/FeS form a copper matte that is progressively oxidised to blister copper); REDUCTION BY CARBON (coke, for metals that don't form carbides at the reduction temperature, e.g. ZnO + C → Zn + CO); REDUCTION BY HYDROGEN (for metals less electropositive than H, e.g. Fe3O4 + 4H2 → 3Fe + 4H2O); REDUCTION BY A REACTIVE METAL (the aluminothermic/Goldschmidt process, e.g. Cr2O3 + 2Al → 2Cr + Al2O3, ignited by a Mg/BaO2 mixture; or reduction by Na, Mg, Ca for oxides such as B2O3, TiO2); and AUTO-REDUCTION, where roasting alone yields the free metal with no separate reducing agent, as for mercury from cinnabar, HgS + O2 → Hg + SO2. A FLUX is any substance added to combine with infusible gangue and form an easily fusible SLAG (a basic flux like CaO for acidic silica gangue; an acidic flux like silica for basic gangue such as FeO).