Extraction of Iron — Revision Notes

⚡ 30-Second Revision

Ores — Hematite ($Fe_2O_3$), Magnetite ($Fe_3O_4$).
Raw Materials — Ore, Coke ($C$), Limestone ($CaCO_3$).
Blast Furnace Zones & Temp — Combustion (1500-1900°C), Slag Formation (1000-1300°C), Reduction (400-900°C).
Key Reactions

- $C + O_2 \rightarrow CO_2$ (Combustion) - $CO_2 + C \rightarrow 2CO$ (CO formation) - $Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2$ (Reduction by CO) - $FeO + C \rightarrow Fe + CO$ (Direct reduction by C) - $CaCO_3 \rightarrow CaO + CO_2$ (Limestone decomposition) - $CaO + SiO_2 \rightarrow CaSiO_3$ (Slag formation)

Products — Pig Iron (impure Fe, 3-4% C), Slag ($CaSiO_3$), Blast Furnace Gas.
Reducing Agent — $CO$ (lower temp), $C$ (higher temp).
Flux — Limestone ($CaCO_3$) for acidic gangue ($SiO_2$).

2-Minute Revision

The extraction of iron primarily occurs in a blast furnace, reducing iron oxides like hematite ($Fe_2O_3$). The process starts with concentrating the ore, followed by calcination or roasting. Inside the furnace, a mixture of ore, coke, and limestone is fed from the top, and hot air is blown from the bottom.

Coke acts as both fuel and the source of the reducing agent, carbon monoxide ($CO$). In the bottom zone (1500-1900°C), coke burns to produce heat and $CO_2$, which then reacts with more coke to form $CO$.

In the upper and middle zones (400-900°C), $CO$ reduces iron oxides ($Fe_2O_3 \rightarrow Fe_3O_4 \rightarrow FeO \rightarrow Fe$). Limestone ($CaCO_3$) decomposes to $CaO$ (flux), which reacts with acidic gangue ($SiO_2$) to form molten slag ($CaSiO_3$) in the middle-lower zone (1000-1300°C).

Molten pig iron (impure iron with 3-4% carbon) and slag are tapped from the bottom. Pig iron is further processed into cast iron, wrought iron, or steel. Remember the roles of coke, limestone, and the specific reactions in different temperature zones.

5-Minute Revision

Iron extraction is a pyrometallurgical process centered around the blast furnace. Key iron ores are hematite ($Fe_2O_3$) and magnetite ($Fe_3O_4$). After crushing and concentration (e.g., magnetic separation for magnetite), ores are calcined (heating in absence of air to remove moisture, decompose carbonates) or roasted (heating in air to remove S, As, and convert $FeO$ to $Fe_2O_3$).

Raw Materials for Blast Furnace:

1
Iron Ore — Concentrated and prepared.
2
Coke ($C$) — Fuel (for heat) and source of reducing agent ($CO$).
3
Limestone ($CaCO_3$) — Flux (to remove gangue).

Reactions in Blast Furnace (by Temperature Zone):

Zone of Combustion (Tuyere Zone, 1500-1900°C, bottom)

* $C_{(s)} + O_{2(g)} \rightarrow CO_{2(g)}$ (Exothermic, provides heat) * $CO_{2(g)} + C_{(s)} \rightarrow 2CO_{(g)}$ (Formation of primary reducing agent)

Zone of Reduction (Shaft Zone, 400-900°C, upper & middle)

* $3Fe_2O_{3(s)} + CO_{(g)} \rightarrow 2Fe_3O_{4(s)} + CO_{2(g)}$ (Initial reduction) * $Fe_3O_{4(s)} + CO_{(g)} \rightarrow 3FeO_{(s)} + CO_{2(g)}$ * $FeO_{(s)} + CO_{(g)} \rightarrow Fe_{(s)} + CO_{2(g)}$ (Main reduction by CO) * At higher temp in this zone (>800°C): $FeO_{(s)} + C_{(s)} \rightarrow Fe_{(s)} + CO_{(g)}$ (Direct reduction by C)

Zone of Slag Formation (Bosh Zone, 1000-1300°C, middle-lower)

* $CaCO_{3(s)} \rightarrow CaO_{(s)} + CO_{2(g)}$ (Decomposition of flux) * $CaO_{(s)} + SiO_{2(s)} \rightarrow CaSiO_{3(l)}$ (Slag formation, $SiO_2$ is acidic gangue)

Products:

1
Pig Iron — Molten iron (3-4% C, brittle), tapped from bottom. Precursor for other irons.
2
Slag ($CaSiO_3$) — Floats on pig iron, used in cement/roads.
3
Blast Furnace Gas — Recycled for preheating.

Key Differences:

Pig Iron — High C (3-4.5%), brittle, from blast furnace.
Cast Iron — 2.5-4% C, brittle, good for casting.
Wrought Iron — <0.25% C, purest, malleable, ductile, tough.

Prelims Revision Notes

1
Iron Ores — Hematite ($Fe_2O_3$, 70% Fe, non-magnetic), Magnetite ($Fe_3O_4$, 72% Fe, magnetic), Siderite ($FeCO_3$), Limonite ($2Fe_2O_3 cdot 3H_2O$).
2
Ore Preparation — Crushing, concentration (gravity/magnetic separation), calcination (heating in absence of air to remove $H_2O$, decompose $CO_3^{2-}$), roasting (heating in air to remove S, As, convert $FeO$ to $Fe_2O_3$).
3
Blast Furnace Raw Materials — Iron ore, Coke (C), Limestone ($CaCO_3$).
4
Role of Coke — Fuel ($C + O_2 \rightarrow CO_2$) and source of reducing agent ($CO_2 + C \rightarrow 2CO$).
5
Role of Limestone — Flux. Decomposes to $CaO$ ($CaCO_3 \rightarrow CaO + CO_2$), which reacts with acidic gangue ($SiO_2$) to form slag ($CaO + SiO_2 \rightarrow CaSiO_3$).
6
Reducing Agents — Carbon monoxide ($CO$) at lower temperatures (400-900°C) and carbon ($C$) at higher temperatures (>900°C).
7
Key Reduction Reactions

* $3Fe_2O_3 + CO \rightarrow 2Fe_3O_4 + CO_2$ (400-700°C) * $Fe_3O_4 + CO \rightarrow 3FeO + CO_2$ (700-900°C) * $FeO + CO \rightarrow Fe + CO_2$ (700-900°C) * $FeO + C \rightarrow Fe + CO$ (>900°C)

1
Temperature Zones

* Top (400-700°C): Initial reduction by CO. * Middle (700-1300°C): Further reduction by CO, limestone decomposition, slag formation. * Bottom (1300-1900°C): Combustion of coke, direct reduction by C, melting of iron and slag.

1
Products

* Pig Iron: Molten, impure iron (3-4.5% C, Si, Mn, P, S). Brittle. Used for cast iron and steel. * Slag: Molten calcium silicate ($CaSiO_3$). Lighter, floats on iron. Used in cement, roads. * Blast Furnace Gas: Recycled for preheating.

1
Forms of Iron

* Pig Iron: Most impure, highest C. * Cast Iron: 2.5-4% C, brittle, good for casting. * Wrought Iron: <0.25% C, purest commercial iron, malleable, ductile, tough, corrosion-resistant. * Steel: Alloy of Fe with 0.1-1.5% C and other elements.

Vyyuha Quick Recall

To remember the raw materials for the blast furnace: Coke, Ore, Limestone, Hot Air. Think: C.O.L.H.A. (Coal-ha, like 'coal haul').