Copper matte consists of \(\mathrm{Cu}_2 \mathrm{~S}\) along with some unchanged FeS. When a blast of hot air is passed through molten matte placed in silica lined converter, \(\mathrm{FeS}\) present in matte is oxidised to \(\mathrm{FeO}\) which combines with silica \(\left(\mathrm{SiO}_2\right)\) to form \(\mathrm{FeSiO}_3\) slag.
\(\begin{aligned}
&2 \mathrm{FeS}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{FeO}+2 \mathrm{SO}_2 \\
&\mathrm{FeO}+\underset{\text { Silica }}{\mathrm{SiO}_2} \longrightarrow \underset{\text { Slag }}{2} \mathrm{FeSiO}_3
\end{aligned}\)
When whole of iron has been removed as slag, some of the \(\mathrm{Cu}_2 \mathrm{~S}\) undergoes oxidation to form \(\mathrm{Cu}_2 \mathrm{O}\) which then reacts with more \(\mathrm{Cu}_2 \mathrm{~S}\) to form copper metal
\(\begin{aligned}
&2 \mathrm{Cu}_2 \mathrm{~S}+3 \mathrm{O}_2 \longrightarrow 2 \mathrm{Cu}_2 \mathrm{O}+2 \mathrm{SO}_2 \\
&2 \mathrm{Cu}_2 \mathrm{O}+\mathrm{Cu}_2 \mathrm{~S} \longrightarrow 6 \mathrm{Cu}+\mathrm{SO}_2
\end{aligned}\)
Thus, copper matte is heated in silica lined converter to remove \(\mathrm{FeS}\) present in matte as \(\mathrm{FeSiO}_3\) slag.