In the LD (Linz-Donawitz) steelmaking process, impurities such as silicon and carbon are removed from molten iron.
Silicon is oxidized to form silicon dioxide ($\text{SiO}_2$), while carbon is oxidized to carbon monoxide (CO).
The reason silicon is removed before carbon lies in the thermodynamic stability of $\text{SiO}_2$, which is greater than that of CO under the conditions inside the converter.
This means silicon oxidizes more readily than carbon, even if its concentration is lower, making it the first to be removed.