What is the function of `SiO_(2)` in the metallurgy of copper?

Explanation

During roasting copper pyrites are converted into a mixture of FeO and `Cu_2O`
`2CuFeS_2+O_2overset(Delta)toCu_2S+2FeS+SO_2`
`2Cu_2S+3O_2overset(Delta)to2Cu_2O+2SO_2`
`2FeS+3O_2to2FeO+2SO_2`
To remove FeO (basic) an acidic flux silica is added during smelting FeO then combines with `SiO_2` to form ferrous silicate `(FeSiO_3)` slag which floats over molten matte and hence can be easily removed.
`FeO+SiO_2toFeSiO_3`
Thus, the role of silica in the metallurgy of copper is to remove ferrous oxide as slag.