Extraction Processes for Copper from Copper Pyrites

To determine the correct steps involved in the extraction of copper from copper pyrites ($\text{CuFeS}_2$), let us analyze each option based on metallurgical principles:

1. Option A: Crushing followed by concentration of the ore by froth-flotation

   • Copper pyrite ($\text{CuFeS}_2$) is a sulfide ore. Sulfide ores are preferentially wetted by pine oil and are concentrated using the froth-flotation process after initial crushing and pulverization.
   • Therefore, Option A is correct.

2. Option B: Removal of iron as slag

   • During the roasting and smelting processes, iron sulfide ($\text{FeS}$) present in the ore oxidizes to ferrous oxide ($\text{FeO}$): $2\text{FeS} + 3\text{O}_2 \longrightarrow 2\text{FeO} + 2\text{SO}_2\uparrow$
   • Silica ($\text{SiO}_2$) is added as a acidic flux, which reacts with $\text{FeO}$ to form a fusible slag of iron silicate ($\text{FeSiO}_3$): $\text{FeO} + \text{SiO}_2 \longrightarrow \text{FeSiO}_3 \quad (\text{Slag})$
   • This slag floats on top and is skimmed off, removing iron from the molten matte.
   • Therefore, Option B is correct.

3. Option C: Self-reduction step to produce 'blister copper' following evolution of $\text{SO}_2$

   • In the Bessemer converter, a part of cuprous sulfide ($\text{Cu}_2\text{S}$) is converted into cuprous oxide ($\text{Cu}_2\text{O}$): $2\text{Cu}_2\text{S} + 3\text{O}_2 \longrightarrow 2\text{Cu}_2\text{O} + 2\text{SO}_2\uparrow$
   • The remaining $\text{Cu}_2\text{S}$ undergoes self-reduction with the formed $\text{Cu}_2\text{O}$: $2\text{Cu}_2\text{O} + \text{Cu}_2\text{S} \longrightarrow 6\text{Cu} + \text{SO}_2\uparrow$
   • The rapid escape of dissolved $\text{SO}_2$ gas during the solidification of molten copper creates blisters on the metal surface, giving rise to blister copper ($\sim 98\text{--}99\%$ pure).
   • Therefore, Option C is correct.

4. Option D: Refining of 'blister copper' by carbon reduction

   • 'Blister copper' is purified further using electrolytic refining (or thermal refining known as poling), not by carbon reduction. Carbon reduction is unsuitable for refining copper as copper has a low affinity for carbon and requires high temperatures where copper carbide formation or re-oxidation can occur.
   • Therefore, Option D is incorrect.

Conclusion: The correct choices are A, B, and C.