Extraction of Iron from Hematite
Section: 9. Metals | Syllabus: Cambridge AS Level Physics 9702
Introduction to Iron Extraction Iron is the second most abundant metal in the Earth's crust (after aluminium) and is one of the most important metals in modern industry. It is extracted from its ore, hematite , using a blast furnace.
Hematite The main ore of iron, composed of iron(III) oxide (Fe₂O₃). It is a reddish-brown rock found in large quantities worldwide. Why Reduction with Carbon? Iron is below carbon in the reactivity series, so it can be extracted by reduction with carbon.
This makes iron extraction much cheaper than extracting more reactive metals like aluminium (which requires electrolysis). The Blast Furnace Blast Furnace A large steel tower lined with heat-resistant bricks, where iron ore is reduced to iron using carbon monoxide at temperatures around 1500°C.
Interactive Diagram Detailed cross-section of a blast furnace showing: (1) Tall cylindrical structure (30-60m high) with thick steel walls and heat-resistant brick lining. (2) Input materials at top: iron ore (Fe₂O₃), coke (C), and limestone (CaCO₃) being added via hopper.
(3) Hot air blast entering near bottom through pipes labeled "preheated air at 1000°C". (4) Internal zones labeled with temperatures: top zone ~200°C, middle zone ~800°C, bottom zone ~1500°C. (5) Chemical reactions labeled at different heights showing equations.
(6) Bottom showing two taps: one for molten iron (dense, at bottom) and one for molten slag (less dense, floating on top). (7) Waste gases (CO₂, N₂) exiting from top. Use color coding: orange/red for hot zones, blue arrows for air input, brown for ore, black for coke, gray for limestone, orange liquid for iron, gray liquid for slag.
Structure of the Blast Furnace: Tall tower (30-60 meters high) made of steel Lined with heat-resistant refractory bricks (can withstand 1500°C+) Materials added at the top Hot air blasted in near the bottom Molten iron and slag removed from the bottom Temperature increases from top (200°C) to bottom (1500°C) Raw Materials (Inputs) Three main materials are added to the top of the blast furnace: Material Chemical Formula Purpose Iron ore (Hematite) Fe₂O₃ Source of iron Coke C (almost pure carbon) Fuel and reducing agent Limestone CaCO₃ Removes impurities (makes slag) Hot air Mainly O₂ and N₂ Allows coke to burn, provides heat What is Coke?
Coke is made by heating coal in the absence of air. It is almost pure carbon and burns at very high temperatures, making it ideal for use in the blast furnace. Chemical Reactions in the Blast Furnace The extraction of iron involves several chemical reactions occurring at different temperatures in the furnace: Stage 1: Burning Coke (Bottom of Furnace, ~1500°C) Coke burns in hot air: C(s) + O₂(g) → CO₂(g) Carbon + Oxygen → Carbon dioxide This is an exothermic reaction - releases heat to maintain high temperature Stage 2: Formation of Carbon Monoxide (Middle of Furnace, ~800°C) Carbon dioxide reacts with more hot coke: CO₂(g) + C(s) → 2CO(g) Carbon dioxide + Carbon → Carbon monoxide Carbon monoxide is the actual reducing agent Stage 3: Reduction of Iron Ore (Upper-Middle Zone, ~800°C) Iron(III) oxide is reduced by carbon monoxide: Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g) Iron(III) oxide + Carbon monoxide → Iron + Carbon dioxide This is the key reaction that produces iron Identifying Redox Reduction: Fe₂O₃ loses oxygen to become Fe (iron ore is reduced) Oxidation: CO gains oxygen to become CO₂ (carbon monoxide is oxidized) This is a redox reaction - reduction and oxidation occur together.
Stage 4: Removal of Impurities - Limestone Decomposition Limestone thermally decomposes: CaCO₃(s) → CaO(s) + CO₂(g) Calcium carbonate → Calcium oxide + Carbon dioxide This is thermal decomposition at high temperature Stage 5: Formation of Slag Calcium oxide reacts with impurities (mainly silicon dioxide/sand): CaO(s) + SiO₂(s) → CaSiO₃(l) Calcium oxide + Silicon dioxide → Calcium silicate (slag) Slag is molten and less dense than iron, so it floats on top Purpose of Limestone Iron ore contains impurities like sand (SiO₂) which would make the iron brittle.
Limestone is added to remove these impurities by forming slag , which can be tapped off separately. Products of the Blast Furnace Product Description Use Molten iron Dense, liquid iron at 1500°C Contains ~4% carbon Tapped from bottom, used to make steel or cast into blocks Slag Molten calcium silicate (CaSiO₃) Less dense, floats on iron Road building, cement manufacture, concrete aggregate Waste gases Mainly CO₂ and N₂ Also some unreacted CO Exit from top - CO can be burned as fuel to heat incoming air Diagram Visual showing the two tapping points at bottom of blast furnace.
Left tap: molten iron (orange/red) flowing out, labeled "Molten iron - denser, sinks to bottom, 1500°C, contains ~4% carbon". Right tap (higher up): molten slag (gray) flowing out, labeled "Molten slag - less dense, floats on iron, used for road building".
Show cross-section with layers: bottom layer of iron (dark orange), top layer of slag (light …
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