1. Identify the metallurgy involved

Copper is commonly extracted from copper pyrite, $CuFeS_2$, a sulphide ore. The usual steps in extraction are:

• Crushing and grinding
• Concentration by froth flotation
• Roasting/smelting
• Removal of iron as slag
• Formation of copper matte
• Self-reduction to give blister copper
• Electrolytic refining

2. Check Option A

A: crushing followed by concentration of the ore by froth flotation

Since $CuFeS_2$ is a sulphide ore, it is concentrated by froth flotation method after crushing and grinding.

So, A is correct.

3. Check Option B

B: removal of iron as slag

During smelting, iron sulphide gets oxidized:

$2FeS + 3O_2 \rightarrow 2FeO + 2SO_2$

Then silica is added as flux, and iron oxide is removed as slag:

$FeO + SiO_2 \rightarrow FeSiO_3$

Thus iron is removed as ferrous silicate slag.

So, B is correct.

4. Check Option C

C: self-reduction step to produce 'blister copper' following evolution of $SO_2$

After formation of copper matte, some copper sulphide and copper oxide are present. Then self-reduction occurs:

$2Cu_2O + Cu_2S \rightarrow 6Cu + SO_2$

This produces blister copper, and $SO_2$ is evolved. The blister appearance is due to escaping $SO_2$ gas.

So, C is correct.

5. Check Option D

D: refining of ‘blister copper’ by carbon reduction

Blister copper is not refined by carbon reduction. It is refined mainly by electrolytic refining.

Hence, D is incorrect.

6. Final answer

The correct options are:

$\boxed{A,\ B,\ C}$

7. Comparison with stored correct answer

Stored correct answer: A, B, C

My derived answer matches the stored correct answer.