How iron is made from rock
Reduction of iron ore by carbon monoxide · Redox · Reduction
Every steel paperclip started as red rock that had its oxygen pulled out by carbon monoxide.
Reactants approach
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ΔH = -25 kJ · exothermic, releases heat
ΔH per mol Fe2O3, at 25 °C.
Meet the molecules
- Reactantsolid
Fe2O3
iron(III) oxide (hematite)
- Reactantgas
CO
carbon monoxide
- Productsolid
Fe
iron
- Productgas
CO2
carbon dioxide
What you notice
Almost every steel object, from cars to paperclips, began as iron ore such as hematite, Fe2O3, a reddish rock mined mainly in Australia and Brazil. In a blast furnace up to 30 m tall, ore, coke (nearly pure carbon made from coal) and limestone are fed in at the top while hot air is blown in near the bottom. Temperatures near the base reach about 2000 °C, and molten iron collects there to be drained off several times a day. Around 1.3 billion tonnes of iron are made this way each year, a major source of CO2.
Safety: Carbon monoxide, the reducing agent here, is a colourless, odourless poison, so steelworks monitor it continuously.
Step by step
- 1
Coke burns
Near the bottom, coke burns in the blast of hot air to CO2, releasing heat.
- 2
Carbon monoxide forms
Higher up, CO2 meets more hot coke and is reduced: CO2 + C → 2CO. Carbon monoxide does most of the work of reducing the ore.
- 3
Oxygen is stripped from iron
As the ore sinks, CO removes its oxygen in stages (Fe2O3 → Fe3O4 → FeO → Fe), each CO becoming CO2. Each Fe3+ ion gains three electrons.
- 4
Iron melts and drips
The iron absorbs some carbon, which lowers its melting point, and trickles down to pool at the base under a layer of slag.