JEE Main · 2023 · 25 Jan 2023 · Shift 1 · General Principles and Processes of Isolation of Metals

During the extraction of copper the sulphide ores are first roasted, as in $2\mathrm{C}{\mathrm{u}}_2\mathrm{S}+3{\mathrm{O}}_2\to 2\mathrm{C}{\mathrm{u}}_2\mathrm{O}+2\mathrm{S}{\mathrm{O}}_2$ and $2\mathrm{FeS}+3{\mathrm{O}}_2\to 2\mathrm{FeO}+2\mathrm{S}{\mathrm{O}}_2$. The iron(II) oxide so formed is then slagged off with silica as acidic flux, $\mathrm{FeO}+\mathrm{Si}{\mathrm{O}}_2\to \mathrm{FeSi}{\mathrm{O}}_3$. The combination of lime with silica, $\mathrm{CaO}+\mathrm{Si}{\mathrm{O}}_2\to \mathrm{CaSi}{\mathrm{O}}_3$, is the slag-forming step of the blast-furnace extraction of iron, where $\mathrm{CaO}$ acts as the basic flux, and it has no place in the metallurgy of copper. Hence the reaction that does not occur during the extraction of copper is $\mathrm{CaO}+\mathrm{Si}{\mathrm{O}}_2\to \mathrm{CaSi}{\mathrm{O}}_3$.