“We must trust to nothing but facts: These are presented to us by Nature, and cannot deceive. We ought, in every instance, to submit our reasoning to the test of experiment, and never to search for truth but by the natural road of experiment and observation.” ― Antoine Lavoisier, Elements of Chemistry

Tuesday, 21 November 2017


Iron is only a moderately reactive metal - but it is less reactive than Carbon.

Because of this is can be smelted displaced from Iron compounds by heating with Carbon (coke).

Iron compounds are found in rocks - we call rocks with high percentages of Iron compounds Iron ore.

The best known Iron ore is called Haematite (Haem - means Iron, as in Haemoglobin)

It contains Iron Oxide and many  impurities.

It is dropped into the top of a blast-furnace along with Coke (purified Coal, almost pure Carbon) and Limestone (Calcium Carbonate).

Hot air is blasted in from the side to provide Oxygen that allows some of the Carbon to burn, releasing enough heat to raise the temperature above 1500oC.

Carbon + Oxygen --> Carbon Dioxide
C (s)  + O2(g) --> CO2(g)

However, not enough Oxygen is added for complete combustion so some Carbon Monoxide is made.

Carbon Dioxide + Carbon --> Carbon Monoxide
CO2(g) + C (s)--> 2 CO(g)

Carbon Monoxide is toxic but its presence in the Blast Furnace is important to how the process works because it removes Oxygen from (Reduces) the Iron Oxide to Iron.

Carbon Monoxide + Iron Oxide --> Iron + Carbon Dioxide.

3 CO(g) Fe2O3 (s) --> 2 Fe (l) + 3 CO2(g)

The Iron is dense and liquid and so flows to the bottom of the furnace.

The Carbon Dioxide escapes at the top.

If the impurities in the Iron Ore were allowed to mix in with the Iron it would be brittle and useless.

But the Limestone breaks down (thermally decomposes) to form Lime which then reacts with the sandy impurities

Calcium Carbonate (Limestone) --> Calcium Oxide (Lime) + Carbon Dioxide
CaCO3 (s) --> CaO (s) + CO2(g)

Calcium Oxide + Silicon Oxide (sandy impurities) --> Calcium Silicate (Slag)
CaO (s) +SiO2(s) --> CaSiO3(l)

The slag also flows to the bottom of the furnace but is less dense than the Iron and so floats on top, allowing them both to be tapped off separately.

source: https://sites.google.com/site/internationalgcsechemistry/year-10-topics/extraction-and-uses-of-metals/3---extracting-iron

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