Question

What is the flux used in the extraction of cast iron from hamatite ore?

Answer 1

The flux is limestone (calcium carbonate).

Explanation:

The limestone decomposes at about 1000 °C to form `"CaO"` and `"CO"_2`.

`"CaCO"_3 → "CaO + CO"_2`

`"CaO"` is a basic oxide, so it reacts with the acidic oxides in the ore (mainly `"SiO"_2`) to form slag, which is mainly calcium silicate.

`underbrace("CaO")_color(red)("basic oxide") + underbrace("SiO"_2)_color(red)("acidic oxide") → underbrace("CaSiO"_3)_color(red)("a salt")`

The slag melts and floats over the denser molten iron, and openings in the side of the furnace allow them to run off separately.