Question

The addition of silica during the extraction of copper from its sulphide ore

• A. converts copper sulphide into copper silicate
• B. reduces copper sulphide into metallic copper
• C. converts iron oxide into iron silicate
• D. reduces the melting point of the reaction mixture

Hint:

In metallurgy, remember the key principle: an acidic flux (like SiO$_2$) is used to remove a basic impurity (like FeO, CaO), and a basic flux (like CaO) is used to remove an acidic impurity (like SiO$_2$, P$_4$O$_{10}$).

Answer 1

The Correct Option is C

To understand the role of silica in the extraction of copper from its sulphide ore, we must delve into the metallurgical process involved. The main ore for copper extraction is Copper Pyrite (CuFeS₂).

The extraction of copper involves the following steps:

1. Concentration of Ore: The ore is concentrated by froth flotation to remove large amounts of impurities.
2. Roasting: The concentrated ore is roasted in the presence of oxygen, which leads to the formation of iron oxide (FeO) and sulfur dioxide (SO₂). The key reactions are:
   2CuFeS_2 + O_2 \rightarrow Cu_2S + 2FeO + 2SO_2
3. Formation of Slag: Silica (SiO₂) is added as a flux to remove impurities in the form of slag. The iron oxide reacts with silica to form iron silicate (FeSiO₃). This slagging reaction is crucial because it separates the undesired iron content from the copper matte. The reaction is:
   FeO + SiO_2 \rightarrow FeSiO_3
4. Formation of Copper Matte: The remaining copper sulphide (Cu₂S) forms the matte, which is then further processed to obtain copper.

From the explanation above, it is clear that the correct answer is: "converts iron oxide into iron silicate". This step is vital as it helps in removing unwanted iron oxides in the form of slag, allowing the copper to be more easily extracted.

Let's rule out the other options:

• Option 1: "converts copper sulphide into copper silicate" – Silica does not react with copper sulphide to form copper silicate.
• Option 2: "reduces copper sulphide into metallic copper" – The reduction of copper sulphide into metallic copper is achieved in the converting process, not directly by the addition of silica.
• Option 4: "reduces the melting point of the reaction mixture" – While fluxes can alter melting points, the primary purpose of silica here is to react with iron oxide to form slag.

Thus, the primary function of adding silica is indeed to convert iron oxide into iron silicate, which helps in efficiently removing impurities from the ore.