JEE Main 2023 · 30 January · morning · Single correct · +4 / −1
In the extraction of copper, its sulphide ore is heated in a reverberatory furnace after mixing with silica to:
- (a) remove FeO as FeSiO₃
- (b) remove calcium as CaSiO₃
- (c) decrease the temperature needed for roasting of Cu₂ S
- (d) separate CuO as CuSiO₃
Answer and solution
Answer (a) remove FeO as FeSiO₃
Solution
Chemistry ma’am · 4 steps
Silica is the acidic flux here: it grabs the basic FeO and carries the iron away as slag.
- Iron is the impurity. The common copper ore is copper pyrites, CuFeS₂, so iron comes along with copper. On heating, part of the iron sulphide is oxidised to FeO, which is a basic oxide.
- Silica as flux. SiO₂ is acidic, so it reacts with the basic FeO to form fusible iron silicate slag. The slag is light and floats on top, so it can be run off.
FeO + SiO₂ → FeSiO₃
- Copper stays behind. Copper has a greater affinity for sulphur than iron does. Any copper oxide formed is converted back by Cu₂O + FeS → Cu₂S + FeO, so copper remains in the matte (Cu₂S with a little FeS) while iron goes into the slag.
- So. Silica is added to remove iron oxide as FeSiO₃ slag. The answer is (a).
The idea to keep. Match the flux to the impurity by opposite nature: a basic impurity like FeO needs an acidic flux like SiO₂, and an acidic impurity like SiO₂ needs a basic flux like CaO.
Answer from the NTA final answer key. Solution by PrepWiser.