[cliverlong]

Hi,

     Looking at a simple reactivity series, Carbon is more reactive than Iron. So simplistically, I would have thought Carbon would be able to reduce Iron(III) Oxide to Iron and Carbon Dioxide. However, the reducing agent seems to be Carbon Monoxide? Why is this so i.e. why is Carbon not the reducing agent as its position in the Reactivity series would suggest? How is that path involving Carbon Monoxide determined given the high temperatures in a blast furnace?


Thanks

Clive

[Arkcon]

Simply put, historically, a blast of heated air was used to thermally decompose iron ore and melt iron.  It wasn't possible to mix iron ore, carbon, and get it hot enough by burning the carbon.  The exothermic reactions of carbon with oxygen in the air, carbon monoxide with iron oxides, etc were needed to get usable iron.  Furthermore, the residual reducing power of carbon monoxide shields the iron from atmospheric oxygen, until a slag can form to also shield it.

Now in modern times, an electric arc furnace, charged with iron ore, scrap, carbon and free oxygen, can work just fine, before the carbon monoxide generation starts happening, anyway.

But in reality, way more is happening than just the reduction of iron oxides to free iron.  Even today, iron smelting is as much art as it is science, small amounts of carbon (and other elemental,) impurities alter the crystal types that grow in th pig iron mass, changing it's physical properties.