Question

What flux would you use to remove the following impurity?

FeO

Answer 1

The impurity FeO (ferrous oxide) is basic in nature. To remove it, an acidic flux such as SiO₂ (silica) is used.

\[\ce{FeO + SiO2 -> FeSiO2}\]

So, the flux used to remove FeO is SiO₂ (acidic flux).