State the role of silica in the metallurgy of copper.

Explanation

During roasting, copper pyrites are converted into a mixture of FeO and `Cu_2O`,
`underset("Copper pyrites")(2CuFeS_2+O_2) overset(Delta)to Cu_2S + 2FeS + SO_2`
`2Cu_2S + 3O_2 overset(Delta)to 2CuO + 2SO_2`
`2FeS + 3O_2 to 2FeO + 2SO_2`
During this process, FeO acts are basic impurities and to remove it we add silica `(SiO_2)` as acidic flux. FeO combines with `SiO_2` to form slag and can be removed easily.
`FeO + underset("Flux")(SiO_2) to underset("Slag")(FeSiO_3)`