The Blast Furnace | Rock to Rail

Step 0 · What goes in

The Charge

Four raw materials go into a blast furnace. Get these right and the rest of the process — and your poster — falls into place.

Iron ore

Haematite, Fe₂O₃

The source of iron itself. It's an oxide — iron chemically bonded to oxygen — so it has to be reduced to get pure iron out.

Coke

Carbon, C

Made by heating coal without air. It's the fuel and the reducing agent — it does the actual job of removing oxygen from the ore.

Limestone

Calcium carbonate, CaCO₃

The flux. It reacts with sandy impurities (silica) in the ore to form slag, which is removed separately from the iron.

Hot air blast

Preheated O₂ / N₂

Blasted in through the tuyeres near the bottom. It's what makes the coke combust and drives the whole furnace's heat.

Step 1 · Inside the furnace

Five zones, top to bottom

A blast furnace runs continuously — materials are added at the top and molten iron is tapped from the bottom, 24 hours a day. As the charge sinks, it passes through zones of rising temperature, each doing a different chemical job. Scroll through and watch the furnace on the left light up.

1 · Throat — loading the charge

~200°C

Iron ore, coke and limestone are tipped in from the top in alternating layers. Nothing chemical happens yet — this is just the charge beginning its slow journey down.

2 · Stack — reduction begins

400–900°C

Hot carbon monoxide gas, rising from lower down, meets the descending iron ore. It pulls the oxygen away from the iron oxide — this is reduction (loss of oxygen).

Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)

This is the single most important reaction in the whole furnace — it's the moment iron ore actually becomes iron. It happens gradually as the ore falls further down and gets hotter.

3 · Bosh — flux and slag

900–1600°C

Limestone decomposes in the heat, releasing carbon dioxide:

CaCO₃(s) → CaO(s) + CO₂(g)

The calcium oxide formed then reacts with silica (sand, SiO₂) — the main impurity in the ore — to form molten slag:

CaO(s) + SiO₂(s) → CaSiO₃(l)

Slag is less dense than iron, so it floats above the molten iron collecting below — which is exactly how the furnace separates them.

4 · Tuyeres — combustion

~1900°C (hottest point)

The hot air blast enters here and the coke bursts into combustion — an exothermic reaction that supplies almost all the heat for the whole furnace:

C(s) + O₂(g) → CO₂(g)

That CO₂ then reacts with more red-hot coke rising past it, producing the carbon monoxide that does the reducing work higher up in the stack:

CO₂(g) + C(s) → 2CO(g)

5 · Hearth — collection and tapping

~1500°C

Molten iron and molten slag collect in the base. Because slag floats, it's tapped off from a higher outlet; the denser molten iron is tapped from a lower outlet at the very bottom, ready to be cast or carried straight to a steelworks.

Step 2 · What comes out

Three outputs

A working furnace doesn't just make iron — everything that comes out of it gets used for something.

Main product

Molten iron

About 96% iron. Still contains carbon and other impurities, so it's brittle — this is "pig iron." Most goes straight on to be turned into steel.

By-product

Slag

Cooled and crushed, slag is sold on — it's used to make road surfaces and as a component of cement.

By-product

Waste gases

The mix of nitrogen, CO and CO₂ leaving the top is captured and burned to preheat the incoming air blast — recycling heat back into the furnace.

Step 3 · Prove it

Check yourself

Five quick questions. No pressure — get one wrong and you'll see why, then you can carry the right answer straight into your poster.

Step 4 · Build it

Poster Toolkit

Everything below is aimed squarely at your iron production poster — tick things off as you plan, and use the tiers to check how far you've pushed it.

Content checklist

All four raw materials named, with their chemical formulas A labelled diagram of the furnace, showing at least the throat, tuyeres and hearth The main reduction equation: Fe₂O₃ + 3CO → 2Fe + 3CO₂ The slag-forming equation: CaO + SiO₂ → CaSiO₃ An explanation of why limestone is added (removing impurities as slag) What happens to each of the three products afterwards Correct use of the words "reduction" and "oxidation"

Suggested structure

Open with a hook — a striking fact or image, not a dictionary definition.
Put one large, clearly labelled diagram at the visual centre of the poster.
Walk the reader through the process in the actual order it happens — top to bottom of the furnace.
Box or highlight your equations so they're not lost in body text.
Finish with a short "why this matters" — where the iron actually goes.

Which tier is your draft in?

Slag

States what the furnace does but doesn't explain how. No equations, or equations copied without explanation.

Pig iron

Correct raw materials and a labelled diagram. At least the main reduction equation is included and briefly explained.

Steel

All key equations present and explained in the right order, slag formation is properly justified, and products are linked to real uses. Reads like you actually understand the furnace, not just memorised it.

Design tips for the poster itself

Pick one accent colour for "hot" zones and one for "cool" zones — colour-code your diagram to match the text around it.
Leave white space. A poster crammed edge-to-edge is harder to mark and harder to read from across a room.
Use arrows to show flow — materials down, gases up — rather than describing direction in a sentence.
Keep font sizes to two or three levels: title, section heading, body. More than that looks noisy.

Reference

Glossary

Haematite: The main iron ore, mostly iron(III) oxide, Fe₂O₃.
Reduction: Loss of oxygen (or gain of electrons) — what happens to iron oxide as it becomes iron.
Oxidation: Gain of oxygen — what happens to carbon as it burns to CO₂.
Reducing agent: A substance that removes oxygen from another — carbon monoxide, in this furnace.
Flux: A substance added to remove impurities — limestone, which reacts with silica.
Gangue: The unwanted rocky material (mainly silica/sand) mixed in with the iron ore.
Slag: Molten calcium silicate — the waste product formed when flux reacts with gangue.
Tuyeres: Nozzles near the base of the furnace through which the hot air blast is forced in.
Exothermic: A reaction that releases heat — coke combustion, which powers the whole furnace.
Pig iron: The impure molten iron tapped from the furnace, roughly 96% iron.